RESEARCH BOARD OF CANADA Translation Series No. 2746

Theory and practice of cultivation method of the . Fisheries multiplication cultivation series

by Isao Matsui'

Original title: Yoman-ho-.Tno riron to jissai; Suisan zo-yoshoku sosho. (Yoman-gyo.no Tebiki) Zoho kaitei ban

Translated by the Translation Bureau( MI ) • Multilingual Services Division Department of the Secretary of State of Canada

ResOurce'Development Branch .sFisheriès and Mariné Service ,Department of ,the .Environment ' Ottawa, KlA ..0H3 •

272 pages typescript DEPARTMENT OF THE SECRETARY OF STATE SECRÉTARIAT D'ÉTAT TRANSLATION BUREAU BUREAU DES•TRADUCTIONS

MULTILINGUAL SERVICES DIVISION DES SERVICES DIVISION MULTILINGUES

_ • CLI ENT'S NO. DEPARTMENT DI VISION/BRANCH CITY NO DU CLIENT MINISTÉRE DI VISION/DIRECTION VILLE

Lnvironment. Fisheries ,Dervice Ottawa, unt. ____ BUREAU NO. LANGUAGE TRANSLATOR (INI TIALS) NO DU BUREAU LANGUE TRADUCTEUR INITIALES)

143855 Japa.nese MI SEP 1 2 1973

Fisheries Multiplication and Cultivation Series (Suisan Zo-yoshoku Sosho) No. 4

Enlarged and Revised Edition A ani(ie tn Pond Culture o r the ,-E1

Theory and Practice of Cultivation Method of the Eel (Yoman-ho no Riron to Jissai) • A Guide to Eel Cultivation Industry

by Isao,MATSUI

Japanese Association of Protection of Marine Resources (Nippon Suisan Shigen Hogo Kyokai) UNEDITED TIU,NSLAION Fer inforrna ion only TRAD:jCii0; ,1 NON REVISEE Informalion soulonwnt

iC$ .-.!OU_I 0-.31

f5 3 0 .21-02U-B33.2 -2 7 L./I/ .

DEPARTMENT OF THE SECRETARY OF STATE SECRÉTARIAT D'ÉTAT TRANSLATION BUREAU BUREAU DES TRADUCTIONS

MULTILINGUAL SERVICES DIVISION DES SERVICES CANADA DIVISION MULTILINGUES

TRANSLATED FROM - TRADUCTION DE INTO - EN Jaoanese English

AUTHOR - AUTEUR

Isao •.T\;•\ Tt TITLE IN ENGLISH - TITRE ANGLAIS Theory and Practice of Cultivation Eethod 7.1f the Eel; Fisheries Multiplication (jultivation Series No.4 (A Guide to Pond Culture of the Eel) Enlarged and Revised Edition TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS) TITRE EN LANGUE ÉTRANGÉRE (TRANSCRIRE EN CARACTÈRES ROMAINS) Yoman-ho no Riron to Jissai; Suisan Zo-yoshoku Sosho No.4 _(Yoman-yo no Tebiki) Zoho Kaitei Ban REFERENCE IN FOREIGN LANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE FOREIGN CHARACTERS. RÉFÉRENCE EN LANGUE ÉTRANGÉRE (NOM DU LIVRE OU PUBLICATION), AU COMPLET, TRANSCRIRE EN CARACTÈRES ROMAINS. n/a

erElftENCE IN ENGLISH - RÉFÉRENCE EN ANGLAIS n/a- I -

PUBLISHER - ÉDITEUR PAGE NUMBERS IN ORIGINAL Association of Protectio DATE OF PUBLICATION NUMÉROS DES PAGES DANS Jaoanese DATE DE PUBLICATION L'ORIGINAL of Narine Resources (Nippon Suisa

Shien Irtogo Yyokai) YEAR ISSUE NO. 119 + 3 VOLUME PLACE OF PUBLICATION ANNéE NUMéRO NUMBER OF TYPED PAGES LIEU DE PUBLICATION NOMBRE DE PAGES Chiyoda-ku, Tokyo, Japan .DACTYLOGRAPHIÉES 1970 n/a n/.a 272

REQUESTING DEPARTMENT TRANSLATION BUREAU NO. MINISTÈRE-CLIENT Environment NOTRE DOSSIER N 0 1/I-3855

BRANCH OR DIVISION Fisheries bervice TRANSLATOR (INITIALS) DIRECTION OU DIVISION TRADUCTEUR (INITIALES)

PERSON REQUESTING DEMANOÈ PAR K ..C. Lucas SEP 1 2 1973

YOUR NUMBER VOTRE DOSSIER N 0

DATE OF REQUEST DATE PE LA DEMANDE u/ o.2173_

V.or ■\10,11 RE \ettSEE teti\ornerit 505.200-10-5 1REV. 2/68 1 71• 3 ■ -21- ,)21.1-'5'333 2

PREFACE TO THE SERIES OF PUBLICATIONS OF THE JAPANESE ASSOCIATION OF PROTECTION OF MARINE RESOURCES Our fisheries industry, which is at the top of production quantities of all the world's fisheries industries, could stand at the most advanced level of the industry in the world if our industry was supported not only by the desire of raising the productivity but also by the rational administra- tion of marine resources and development as well as utilization of the resources on the basis of conserving them for the eternal future. Problems related to the conservation of natural resources are numerous. Indeed it can be said that the fisheries administration policy covers the whole phase of • -establishing-and practicing the natural resource preservation policies. In reality, the more appropriate policy should grasp the actual status of the natural resources by scientific methods, control the quantities of catches, add to and cultivate the existing resources, and improve environmental conditions and other protective measures. Further, policies on stabilization of fisheries *product prices and financial standings of fishermen should be aimed at avoiding mere

increase of productions and catches to get out of the fihancial unbalance. We must understand also that our own natural resource conservation policy is a portion of the world's open • sea policy. That is to say, any claim to propose freedom of the open sea fishery should be accompanied by declaration, practice, and cooporation in preservative and developmental utilization of the world natural resources. As our technologies make progress, and our fisheries producti- vities increase, we feel that our contribution towards the preservation of the world natural resources is increasingly strongly solicited and our efforts in cooperation must be undoubtedly more constructive. In our fisheries industry, which is only a part of our forever progressing national economy, the most important contributions that we fishermen can make towards the well balanced development of the national economy are promoting scientific research of protective cultivation of natural resources, and linking the research efforts and administration in this „industry. Our scientists in this industry already made considerable progress towards our goals, but stabilization of managerial problems in this industry is still unsettled. This gap between the theory and practice should be narrowed probably at the standpoint of well-treating the natural resources, by scientific means and by improving fisheries policies. This association is publishing four different series of publications, fisheries research series, fisheries multiplication and cultivation series, overseas fisheries series, and fisheries policy and administration series, and • we hope that these publications contribute in helping to solve so ni e of the problems that we face in our fisheries industry. We shall be extremely happy if these publications indeed contribute towards stabilization and improvement of our fisheries industry and establishing and practicing better Policies towards the goals. Neither a complete publication nor a lengthy portion of the publications of this association may be excerpted and reproduced without the prior authorization of this association.

• 5

TABLE OF CONTENTS /1

PAGES ORIGINAL TRANSLATED ARTICLE ARTICLE

Introduction 2 6

1 Historical Records and Present Day Status of the Eel Culturing Business

2 Biological Species of Japanese and their Distribution 18 3 Life History of the Eel 15 33 4 Factors Contributing to the Growth of the Eel Culturing Business 19 40 Culture Stock 21 46 le- 5 6 Feed 38 77 7 Environment 49 98 8 Disease and Natural Enemy: Their Prevention and Removal 81 157 9 Cultivation Method and Maintenance of Pond 97 186 10 Marketing 113 222

11 Business Administration 117 226

Refèrences 119 231 6

INTRODUCTION /2 11› The fisheries resources of this country, which largely depended on the natural resources only, since ancient times, has started to show the need for artificial cultivation and further development equivalent to seeding and cultivation in agriculture. Mainly because of the most remarkable economic expansion of this country, various enterprises related to structural improvement of primary industries have sprung out in this country. Consequently, part-time fishermen and farmers with low-productivity farmland and some people in fishing villages which lost fishing ground by land reclamation works for development of seaside industrial zones expressed their desire to start out in the eel culture business, At the same time, suitable reference books for it have been in high demand. Among the reference books already published, Goichi Sago's "Eel Culture Methods" and Kei Abe's "Studies on Fish Culture; , crucian carp and eel", both of which were published before the war, and Toshi Inaba's "Guide Book for Eel Culturing" published after the war are excellent but all of these have been out-of-print for sometime. Under these circumstances, the author was approached by the Japanese Association of Protection of Marine Resources (lappon Suisan Shigen }logo Kyokai), and the first edition of this book was published in 1964, but the books were quickly sold out, while the eel culturing business continued to make a rapid progress. For this reason, the author added a few novel findings and cumulated knowledge in the technology into this new edition. This new edition was, therefore, made to be published largely at the demands of people involved with various phases of eel culturing, and the author wishes that the book contribute to further progress of the eel culture technology. This book perhaps has its own right to be considered as a sister volume to the author's essay "the life's journey of eel", but the material covered in this book is limited to those with practical aspects, especially those related to the industrial production of the eel. The author has taken great pains over this work so that it is useful to every class of reader, from the

• - beginners just about tio -start -the -eel -cmIturing business to established trade men and those who are working at a position of giving guidance to the traders. For the former, the author hopes that the book would be useful for being explanatory and for the latter, being more theoretical. Therefore, it is suggested that the reader make use of the book at his own stand point, selecting the subjects of his choice. The author is fully aware of the fact that there are many examples in which industries made great strides by . invention, discovery or improvement's yielded by hard-working traders' accumulated knowledge, experiences, and, above all, deep thinking. The author wishes that this book could present • a few small hints of improvement to the traders in the fish 8

culture industry and thus become a driving force in improving the status of this industry. The author would like to record his heart-felt thanks to Dr. Toshiichi Okubo and Mr. Ryogo Uehara of Tokyo Fisheries College, members of Hamanako Branch Station of Shizuoka Prefectural Fisheries Testings Station, for their lialuable data and photographs appearing in this book, and to Dr. Zenjiro Kubota and Mr. Tatsumi Ojima for their cooporation in preparation of the figures.

• 1. HISTORICAL RECORDS AND PRESENT DAY STATUS OF THE EEL

CULTURING BUSINESS / 3 It was in 1879 that a Mr. Kurajiro Hattori started his eel culturing business using a fish culture pond of 19,835 m2* in Senda Shinden of Fukagawa-ku, Tokyo. This appears to be the first recorded eel culture in this country and it was followed by a Mr. Senemon Harada's culturing carp and eel in a 69,422 m 2 pond in the garden of Omoto Premises in Niimachi Hamana-county, Shizuoka-prefecture in 1891. The latter is the founder of the eel culturing business, which enjoys its prosperity around the Lake Hamanako. In 1896, Mr. Hikotaro Terada started the business 2 somewhere near Kuwana of Mie-prefecture with a 39,670 m wide pond, and Mr, Yasaburo Okumura in Kanno Shinden, Aicbi-pi-., fPr- ture, and each of these are the founder in the respective area. Mr. Hattori, afore-mentioned, expanded his enter- prise to a 79,339.6 m 2 pond in Fukiage, Maisaka-cho (presently, Hattori-Nakamura Fish Culture Pond) in 1897, and Mr. Terada 2 also created a new pond of 9.917 m in his hometown, Fukuda-cho, Iwata-county, Shizuoka-prefecture in 1898, and another one, 2.777 m2 in Kuwana-county, Mie-prefecture in 1899. Thus, the period of about 20 years between 1879 and 1899 can be considered to be the inauguration period of

*-Translator's Note: For non-metric readers, 1 m2 = 1,196 sq. yd. - 10-

the eel culturé industry in this country. In fact, the foun- dation of the eel culture industry in these three prefectures, Shizuoka, Aichi and Mie, where about 81% of the Japanese cultural eel production had been recorded, was placed in this period. Only after these private enterprises started to present new trends of industrialization around 1897, fisheries stations of the local government started to carry out testings on the eel culture method. Namely, in 1896, Aichi Prefectural Fisheries Testings Station started the first research-oriented eel culture, followed by Shizuoka Prefectural Fisheries TeStings Station in 1904, Fukushima-Prefectural Fisheries Testings Station in 1905, and Kuwana County Fish Culture Station of Mie Prefecture in 1908. Therefore, the period between 1896 and 1908 may be considered to be a research and developmental period. At around this time, the Law of Land Reclamation Subsidary came into force, and a small capital investment could convert a vast open land to a fish culture pond, and at the same time,.the invester's ownership of the land was approved. Local politicians took advantage of this law, and wealthy persons offered the land and fund, and thus the eel culturing industry started to develop further as an anonymous association or as an industrial joint-stock corporation. Conditions of location of the centre of eel culture in the foundation period were to be .close to or in the area where silk industry had been developed well for the easy access - 1 1 -

to silk worm pupae, which was the major feed staff of the eel, and to capital resource of the established enterprises. One of the characteristics of the eel culture business in this period is that the management of the enter- prise was almost completely left in the hands of a pond guard. So that difference in the pond guard's technical capability was reflected directly to the productivity difference of the eel culture pond. At around the same time or around 1910, the depres- sion in agriculture became quite serious, there were many disputes between landowners and tenant farmers, and the crop value -lowered considerably. As a result, many landowners converted farmland into an eel culture pond and the eel culture business prospered„ Quite naturally, the cost of fry or culture stock rose quite high because of the shortage, and the feed, /4 which was almost exclusively silkworm pupae, also called for a higher price. Consequently the silkworm pupae was collected - nationwide and redistributed by agencies. As an old saying has it that "necessity is the mother of invention", a fish culturist in Ishiki-village, Banto-county, Aichi-prefecture 2 attempted the first cultivation of shirasu-eel* in a 231 m wide pond in 1918. Unfortunately this attempt resulted in a failure, but it was the beginning of culturing of eel fry, and in 1920, an extensive study of shirasu-eel was initiated in Aichi Prefectural Fresh Water Cultivation Research Institute

Translauor's Note: Shirasu-. See in page 10 of the original. - 12- of Aichi Prefecture (it later became Toyohashi Fish Culture Testings Station of Fisheries Institute, Department of Agriculture), and the solid foundation of eel fry culture was established. Later on, sardine became available as a substitute of silkworm pupae, lowering and regulating the high cost of the latter. In 1923, a large scale cultivation of shirasu- eel was successfully carried out in an eel culture pond of Tanaka, Otsumura, Horai-county, Aichi-prefecture, and in the sanie year, Shimomura eel culture pond in Izumimura, Atsumi- county started to specialize in fry culture in an industrial scale. From this time on, various prefectural fisheries testings station initiated testings - on cultivation of shirasu- unagi.

Becarl on the:Is/a the pprina hp -hwpfan 1918 and 1924 may be regarded as the initiation period of shirasu- eel cultivation, and at the same time, this period is the one in which the eel culture industry entered into a new era. Under these circumstances, many farmers in Kawajiri, Yoshida-town, Narahara-county which was located on the right- hand shore of the mouth of the river Oigawa, about 13 Km from Yaizu-city, and which had a poor rice crop yield of only about 135 Kg per 991.7 m2 , left the village and the farming to work near Yaizu partly because of the poor yield of their land and partly because of the economic expansion and prosperity around 1920. A resident of the village, Mr. Yasushi Kubota and his companions noted the handsome profit that the eel - 13 - culture brought in elsewhere, and opened up their eel culture business in 1922 utilizing 13,984.2 m2 of abandoned rice field. Because of the excellent result that they obtained, 2 they kept expanding their enterprise to a total of 674,383.2 m of pond in 1931. From this time on, the trend of the society in this county was individualism, and many tenants became independent freeing from their landowners. In 1929, the Law of Industrial Association became effective, and many associa- tions of eel culture fishermen were established and the members purchased feed in a joint account basis, resulting in a higher profit for the members. Thus the union activity became one of the cores of the eel cultUring business. The eel culturing business, however, did not follow a smootlx route towards the prosperity. In 1932, when the economy of Japan started to fall into the bottom of depression, the price of cultured eel dropped tremendously. As a countermeasure, eel canning and export of the products to North America, South America, Hawaii, Mexico and others were attempted. Exportation gained 'a fairly good success but in 1935, over-production of the eel was quite serious and curtailment of the production and maintaining the price were seriously discussed among the traders. In 1937, when the China-Affair broke out and the country was under the war structure, there was certain prosperity because of the war-time economy, but later when the Pacific War became inevitable, the eel industry was - 14-

,almost the first to be placed under war-time economic control, • and the eel production dropped markedly. In 1943, the eel cultivation was completely suspended and the eel culture ponds were converted to rice field, lotus pond and natural fish pond. Immediately after the war, the citizens were more or less under a state of despondency, but after 1948, they stood up for reorganization and reconstruction of the nation. At that time, just about every material resource was under an extreme shortage and moreover, most of them were under the distribution control. Fortunately, however, the eel was /5 classified as a group of miscellaneOus fishes, and its trading was freely done. Consequently, the demand for the eel was

• high and open •throughout the nation, and it was traded Bt a high cost, and the reconstruction of the eel culturing business was quite speedy, and the traders were very eager in increasing the 'production quantity. However, many kinds of fresh fish were still under the control of the yemporary Material Supply Control Law, and there was a restriction in the rapid regrowth of the eel culture industry due to the shortage of the feed. Needless to say, the production was carried out using a black- market feed staff to certain extent. By 1950, when the Law was lifted, all the eel culture ponds previously used were restored to meet the original purpose, and a few novel technical improvements, that is introduction of water stirring devices and rest area for the eol, have been introduced. Since then, - 15 - t,he industry eXpanded and the production multiplied quite rapidly. In 1957, there were so many farmers who wanted to convert their farmland to eel culture pond, and there were problems and conflicts in use of agricultural land. Further later, when the supply and demand of food became stabilized, the nation's position in international ranking improved, and the international trading became lieralized, agricultural policy of this country was shifted from the policy of priority production of rice and wheat to that of rational production to suit the type of available land, and the restriction of this conversion of agricultural land to eel culture ponds no longer was a problem. (Fig. 1) From the year end of 1961 to the spring of 1962, there was a catastrophic poor haul of shirasu-eel, perhaps the worst in the eel culture history, and the previous cost of 5,000 yen* per 3,75 Kg sky-rocketted to 60,000 yen or 70,000 yen, and the trademen were looking for any available cheaper shirasu-eel all over the country. This unfortunate incident, however, served the purpose of advertising nationally how profitable a successful eel culturing business could be, and at the same, local.economic enterprisers started to promote the eel culturing business, as the high economic growth rate stimulated consumption of the eel in every locality of this

* Translator's Note: U.S. 1 dollar.was 360 yen in 1970 when this book was published and currently, July, 1973, it is 269 yen,' - 16- • country. In these recent years, even a formation of aggregated eel culturing zones by structure reformation of agriculture and fisheries industries is becoming popular. The inherent instability of shirasu-eel haul promoted import from Taiwan, Korea, France, Philippines and other countries, producing a result comparable to an international trading. As data for analysis of the present day status of the eel culture industry, a recent statistical material of •

eel production may be compared with that in 1942, when the product hit the peak of before the war.

(Table 1)

In 1942, the'haul of natural eel was 2,578 tons, • and the produttion - of -cuItivated eel . was -9Ï821 -tons, making a total yield of 12,399 tons, and yield of the cultivated eel was about 3.5 times as much as that of natural eel.. The data

in 1967 shows that the total yield was 22,767 tons, and the /7

yield of cultured eel was 19,600 tons (86.0%) and that of

natural eel was 3,200 tons (14.0%). The major areas of natural

eel production in 1963 were Iharaki-prefecture (438 tons),

Chiba-prefecture (262 tons), Okayama-prefecture (215 tons),

Kochi-prefecture (204 tons) and three prefectures of Shi'mane,

Miyazaki and Kumamoto (all in a range between 102 and 113 tons). The major areas of cultural eel production are

Shizuoka-prefecture (6,679 tons) (68% of total national • cultural eel production of the year) and Aichi-prefecture - 17 -

(2,448 tons) (about 25%), and these two prefectures produce about 68 of the total national production. These are followed by Mie-prefecture (620 tons, 6%), Tokushima-prefecture

(71 tons) and Oita-prefecture (55 tons). Although other production areas are scattered all over the country, the farthest northerly limit is near Sendai, Miyagi-prefecture, but even farther north in Hokkaido, a successful tunnel type, eel culture testings utilizing the heat of hot-spring has been carried out and its industrialization is expected to take place shortly. In Kyushu, salt water semi-circulation culture method is becoming popular. Therefore, in the very near future, eel production in every locà1 area would expand and supply a sufficient quantity of eel for the local consumption. According to the world statistics of eel production

in 1968, Japan was at the top with production of 26,700 tons, and also with the highest production increase rate, followed by Denmark with 3,200 - 4,700 tons, which was about 1/8 of the Japanese production. Although Italy and Holland have quite variable production from year to year, they have an average production quantity of 1,600 - 4,800 tons. Germany before the war, had about the same production as those of Italy and Holland, its present day production is not too.clear.

The 1968 statistics showed that the production of West Germany was 600 tons. Sweden had 1,700 tons, France 900 - 2,600 tons, Great Britain, U.S.A. and Norway had 200 - 600 tons or less

than 1,000 tons.

•

• - 18-

2. .T3IOLOGICAL SPECIES OF JAPANESE EELS AND THEIR DISTRIBUTION 1) SPECIES There are two species of eel in this country; one is AnRuilla .ilaDonica which is the ordinary species most commonly found in various parts of the country, and the other *1) *2) -is A marmorata, which is called o-eel or kani-kui There are 16 species of eel in the world and 3 of them are further divided into two sub-species and therefore, there are 19 species of eel, including the sub-species. (Fig. 2) (Fig e 3) /8 All these species of eel can be divided into two /9 types by the ratio (a-d)/1 ** differential length (a-d) ** ** between the lenRth from the mouth to the first dorsal (d) ** and the length from the mouth to the anus (a) to the total ** body length (1) When this ratio is between 7 and 17%, the eel is called the long dorsal type and when 0 - 5%, it is called the short dorsal type. The former type is the more common and 14 species including 1 species to be divided to 2 *** subspecies belong to this type while only 2 species to be divided to 4 subspecies belong to the latter type. In addition to the length between the mouth and the first and position of the anus, several other anatomical data is used for taxonomical classification of the

■ ■ ■■■■■ ■■■ ■■ .e.d q*.mé...... e..■e■ .■ .■■.....mwemmmemaàawmmme■.I.M ■ IMMM■mmmter.emeeu ■40elw mmmemm q.m i dbmNem ammelmm.eb Translator's Note: 1) literally, large-eel 2) literally, crab-eating. * * Translator's Note: Added by the translatOr. *** Translator's Note: Added by the translator.

--W.tfWegeNtel M.P.HIMIka.mieres 'err "ire.,411146111.21.1,...0411.1.5.11.e -19 -

.eel. They are numbers of the spinal column discs, stripe bones of the gills, and stripes in the pectoral fins and length of the head and the condition of tooth lining. Particularly the number of spinal discs is important. The sipanal disc number is usually called simply ,spinal bone number, but the number increases as habitation area of eels in one and the same species moves from low latitudes to high latitudes. The number is between 100 and 119, and within this range, different species have different numbers, and those species found in the tropics tend to have smaller numbers while those found in the temperate zone have larger numbers. The has the spinal dise number between 112 ,and 119, and the number is the largest of all the eel species. As these_figurae, indicate, the number varies considerably even in one and the same species. Therefore, the number cannot be used to classify closely related species. But the arrangement of teeth of the ùpper jaw is most revealing of the relationship between the eel species to be examined because of its relation to the biological evolution and the phylogeny of the species. The head length is also not useful in determining the phylogeny, but is useful in picking up a group of related species from a mixture of many unidentified species. Japanese eel belong to the genus of apodal fish with no pelvic fins as a -sea-eel and (eel) do. The shape of the head of the fish in this genus look either long, narrow and'sharp looking or short, Wide and round looking. - 20 -

This is caused by the shape of so-called snout or proboscis, the part from the eyes to the pointed end of the head, rather than by the shape of the head. Comparing to the thin fine lips of the former, the latter has thick broad lips. These two different types are called the narrow head type and broad head type, respectively. Both the eel and o-eel belong to the long dorsal fin group, and they may be differentiated by the following points. Eel 0-Eel No speckle (spot) on the Dark brown speckle on the body surface body surface Head length is larger than Head length is smaller the distance between the than the distance between dorsal fin and the anus the dorsal fin and the anus

- Number of the spinal discs Nuffiber of the spinal discs is 112 - 119 is 100 - 110

Body Length 40 - 50 cm, Usually longer than 1 m rarely longer than 1 m The longest body length that the author measured

in the past of the common eel was 129.7 cm, and most of the

eels longer than 50 cm were found to be female, and in fact, /10

all the eels longer than 58 cm could be judged to be female. As described above, the eel found in this country is only one species, but it is often called many different names for the purposes of business, or according to the practical customs and conveniences. Just as every locality in this country has its own dialect, names of the eel also vary from One area to another. Distinct difference in naming - 21 - the eel is found between the general areas* of Kansai and Kanto and even in the same general area, there are significant differences depending on the locality. In Kanto area, the eel is commonly called unagi which is also the academic name of the fish and also much more generalized name of the fish throughout this country, and in Kansai area, the eel is also called mamushi or mamushi- unagi. The various names of eel may be classified as follows, depending on the body shape, size, color, fishing method, age during the cultivation period and so on. (1) Differentiation by the size shirasu or shirasu-unagi: The fries of eel, sea-eel, conger eel, and kara-iwashi have entirely different body shapes from those of their adults, and their bodies are nearly transparent, resembling a willow leaf in their shapes. These fries are called leptocepharus. A shirasu or shirasu-eel**are the young of eels immediately after they have gone through the metamorphosis from leptocepharus along the coast. They are caught in rivers not far from the sea, and are still transparent without precipitated body pigments. They are 55 to 60 cm long and weigh between 0.13 and 0.18 g, or about 2000 to 2,750 of them weigh 375 g. They are also called mekko or shiroko (near the Lake Hamanako), yoroke (near 2u1cuda) or Hamakko (along the river Tenryugawa).

Translator's Note: West and east of Sekigahara (near Nagoya), respectively -. The former area includes Osaka and the latter Tokyo. ** Translator's Note: This may be the same as an elver. - 22 -

Kuroko, Kurokko, Datsu or Dakko: When a shirasu spends about a 1 week period in rivers, its bodY pigment starts to develop and becomes dark. The fry at this stage sometimes becomes smaller and lives only very close to the river mouth. Its anadromous season is after March, and the mixture ratio of kurokko to shirasu in one group of fry increases as the timing of the group of fry going up a river becomes late. Usually, natural kurokko about 55 to 70 mm long is called ten-kuro and this name is specifically used to differentiate it from cultured kUrokko. The size of fry commonly used for the eel culture to bring out adult eel has about 15 to 40 g of body weight and is less than 1 year old after leaving the sea. Meso, mesoko, mesokko or mekko: It is also the stock for zulturing and-usually larger than 38 lo 56-e. It is also called nyumen. Hoso or biri: It is smaller than 56 g and also called memezo- unagi (Kyoto) or zubera (Nagano area). It is also the fry for culturing. Saji: This appears to be slightly larger than meso although it may weigh between 38 - 56 g. It is used for broiling and . served.

* Translator's Note: This author often uses somewhat unusual or perhaps queer figures; such as 38 - 56 g instead of, say 40 g - 55 g, or so many number of fish per 375 g instead of 100 g or 400 g. These weights he chose are based on the traditional Japanese weight unit, that is, 3.75 g . 1 "momme" and 375 g = 1 "kan". By using these figures, which are conversion of the traditional unit to be metric unit, he perhaps tried to make old fishermen understand the subject more easily. - 23 -

Ara: Those larger than 150 to 300 g are called good-are, /11

and 75 to 110 g poor-ara*. The ones weighing between 40 and 75 g are called "upper-middle" and less than 40 g "middle". Kiridashi or - saiman: This is a small eel served as food, but because of little fat, it is considered tasting poor. It is used for "broiled rice served in a bowl". . Yota: This is best suitable for so-called -broiling, and weighs between 94 and 225 g. Boku or bokka: This is a large size eel, weighing more than 250 g. Natural eel is called ten-boku and the cultured one is called yo-boku. The former is uàually larger. The eel has much darker skin color and good skin slick, but the skin is thick and hard and the is too fatty. People in Kansai are fond .of „boku, but it is_considered mot to be tasty in Kanto. Most of the eel products exported are prepared using this class of eel. (2) Differentiation by color Ao**: Its body is fat and round, the back being blue or dark green and abdomen white. It tastes very well and generally favorably accepted, calling for the highest price. In short, this is a synonym of the eel with the best quality. Recently the cultured eel is often called ao or yo. - Kuro***: Its back is black and used to be seen abundantly in the Kojima Bay before its drainage.

...r.0.4■■...m.... ■a...... be ■MmeWpmw.M ■■•*■■amemr■wee*mmemmerabm * Translator's Note: Partly transliterated. gl› ** Translator's Note: Literally blue. *** Translator's Note: Literally black. - 24-

Aka*: Its back is yellowish red. The name is usually used • in Kansai market. Goma** or goma-unagi: Its back is brown while it is a juvenile, but turns to dark brown when it becomes an adult, and its abdomen is pale yellow or white. There are a number of scattered black speckles mainly on the side and abdomen and occasionally on the back. Its distribution is limited, and although its skin is quite hard, it contains a lot of fat and is judged to be delicious. It appears to be a young o-unagi. Saji (in Kanto), ma-unagi***or maio (in Kansai): Its body type is round and fat. The back is either pale black, brown, or greenish brown and the abdomen pale yellow or white. Presence of scales arranged in a mosair is suite distinct. The ,skin is somewhat hard, and the meat rich in fat. It is delicious especially in winter. Its home is supposedly Shinji near Matsue-city or Ghukai. The one produced near Yanagikawa, Ariake is called hoshi. • Kudari****, kudari-unagi or aya (in Kanto), dake (Sanin), sayagata or kaeri: At the time of going down to the sea to lay eggs, the eel produces nupital color, which is characteristic

Mil••••••■•••■■■••••••■•••là Translator's Note: Literally red. #* Translator's Note: Literally sesame. *le* Translator's Note: Literally true-eel. #* * * Translator's Note: Literally running-down (the river). • -25- of the kudari-eel. Generally speaking, the color of ordinary female eel is lighter, and the abdomen of the female eel is yellow and the male eel is bright, clear white before the nupital color starts to show. However, the nupital color of saji is bluish black on the back, copper-red on the side with metallic luster, pink on the abdomen, golden-yellow at the base of the pelvic fins, and violet black on the rest of the body, including the mouth and forehead. Ao produces even darker blue on the back, golden-yellow on the side, pale pink on the abdomen, gold-leaf color at the base of the pelvic fins, and bluish black on the rest of the body including /12 the mouth and forehead. Goma-unagi'produces bluish brown on the back, pale golden yellow on the side, pale pink on the abdomen, violet black on the pelvic fins with clearer black speckles. Geita does not show too clear neputal color e (in Kanto), 'gan and kanikui (in Kansai): Géita, kanikui Its head is quite large, and its body is thick between the back of - the head and a little behind the pelvic fins, but thin between the abdomen and the tail. Its taste is poor and the meat is hard. It is usually classified as the poor eel. (3) Differentiation by age during the cultivation. Yo-biri.*: It is sometimes called the starting material. It is a smaller fry cultivated from the so-called shirasu-unagi, and its size is between 0.8 and 13.0 g. •

* Translator's Note: Yo stands for yoshoku, i.e., cultivation. - 26--

Yo-chu: It is the fry produced from the shirasu-unagi, and specifically cultured to yield yota-unagi, and its size is about 15 to 40 g. Tobi: A group of particularly good yo-biri or yo-chu is called by this name. About 10 to 20% of the fry under cultiva- tion belongs to this group. The traders often call it "first- class child" and are delighted to see it. Eri-shita: Smaller size of cultured eel is called by this naine. Most of the eel in this group are about 80 g of the body weight. Yota: This group of eel can be shipped out to a market, and it weighs between 100 and 200 g. Chu-boku: Quite thick eel, over 320 g (Hamanako) or 250 g (Yoshida area). Ten-biri: Natural fry, when distinguished from the cultured fry. Ten-buto: Thicker than the ten-chu, and about 100 to 150 g. Ten-boku: Extra large natural eel. Sashi-genryo: After taking out yota from a pond to prepare for the market, a fresh batch of fry is introduced into the pond to replace the yota. This is called sashi-genryo (or added starting material). • (4) Differentiation by fishing method. Bosa: Eel caught by the shibatsuke fishing method. "Bose is a bundle of bamboo branches about im long, tied to about three times as thick as a bamboo broom. A number of bosa bundles are placed at 1 to 2m intervals near a river mouth where the stream is slow, in the evening. When they are taken out early in the morning or during the night, eels smuggled themselves into the space among the branches are brought up near the surface, and they are caught with a tri- angular net. Sometimes 2 to 3 kg of eel can be caught with one bosa. Since the eel caught by this method is not injured and taste good, the method is highly favored. This fishing method has its origin in capturing small for cooking. Chasing the , eel is caught in the bosa, which is now used to catch the eel. Tsutsu (tube): Two to three bambooLtubes are tied together after knocking-off the joints, and placed at the bottom of th4, river Rim] entuarpri intn the tilheP are naught, The bambon tube used for this purpose is 7 to 10 cm wide and 60 cm long. In Kansai area, the name "poppo" is also used. Nawa (rope): Eel hooks are attached at lm intervals to a piece of branch-rope. About 500 to 1,000 meter long rope is used as a main rope to which the branch-ropes are attached. It is quite interesting to see that depending on the kinds of bait placed on the hooks, eels of different kinds are caught. For example, if an earthworm or a leech is used, then the eel which lives on it only is caught. A mimizu-nawa (earthworm rope) which uses an earthworm or leech is usually used near Sahara of Chiba-prefecture. In Kasumigaura, a pond-smelt is used as a bait, early . in the ,spring and late in - 28 -

the autumn. In Kansai area, the use of this pond-smelt rope • is supposed to signify the beginning and the end of the eel fishing season.

Saji: All the eel caught by methods other than bosa, tsutsu and nawa is called saji eel. It includes the eel caught with

various nets and buskets. Most of the kudari-unagi caught in the Tone at the beginning of the autumn are caught with nets.

Yana (weir): The eel caught with various kinds of .

Kama: The eel caught by scooping with an eel scoop. Hari (Hook) or Nawa (rope): The eel caught with hook placed at a fixed spot or with the ropedescribed above. Yobiki*: The eel caught during the - night with a drag net resembling the uchise** net, during the night. It is supposed to be the best natural eel. (5) Differentiation for business purpose. The price of fresh or live food like eel varies cOnsiderably from day to day. Therefore, orders and inquiries are mostly done by telephone or telegrams; "u" is the accepted commercial code for unagi (eel). Specifically, the young of eel to be used for the eel culture is abbreviated as tane (seeds) or biri; cultured eels, futo or yota, and other adult eels are coded by the common code Hu n . Dead eel are called agari (ascended or finished) in Tokyo area; josuke, ojosan or oshosan - (priest) in Osaka area.

* Translator's> Note: Literally pulling during the night. • ** Translator's Note: Literally beatin,2; the shallow water, - 29 -

In Kansai, the word hansuke- means the head of the eel. Although certain kinds of fish very closely 1-esemble the eel in that they also have cylinder-like bodies, but they are taxonomically unrelated ..to the eel. They are mekura-unagi*, yatsume-unagi**, toge-unagi, ta-unagi, erabu- unagi and shigi-unagi. 2) DISTRIBUTION Among the 19 species, including subspecies, only two of them are found in the Atlantic while all the other 17 species are distributed in.the Pacific Ocean and the Indian Ocean. One of the two species which are found in the Atlantic Ocean lives on the side of the European Continent and the other on the side of the American Continent. However, /14 in the Pacific Ocean, there are 13 species and in the Indian Ccean, 6 species. There are 2 species known to live both in the Pacific Ocean and the Indian Ocean. Of the 13 species that live in the Pacific Ocean, 10 species live in the southern hemisphere, 5 in the northern hemisphere, and 2 only near the equator (4 species are common), and in the Indian Ocean, 4 species,each are found in northern and southern hemispheres (2 species are common). Most of the eel species are found in the tropics, north and south of the equator, and in fact, this is the water area where the largest number of eel species are found. • * Translator's Note: Probably a hagfish. ** Translator's Note: Probably a lamprey or rock-sucker. - 30 -

PPsides, about 70 of all the eel species found in the Pacific Ocean are mainly found in this area, and for this reason, the tropic Pacific Ocean has been considered to be the birth place of the ancestor of present day eel species. Thus many species live in the tropics but 6 species are found in the temperate zones. The eel species found in the northern hemispheric temperate zone are 3 species, one is the Japanese eel, Amuilla 12:22Eica, which lives in the Pacific and found in Asia, and the others are the , A. anrruilla and the , A. rostrata, both of which live in the Atlantic Ocean. The southern hemis- pheric temperate zone contains also'three species, A. dieffenbachi, A. australis schmidti and A. australis, and all of them are found in New Zealand and Australia waters. In addition to these 6 species, 2 species live in both the tropics and the temperate zones. They are A. mossambica of the Indian Ocean and A. marmorata of the Pacific Ocean, and the latter is also found in the Indian Ocean, and therefore, this is the species most widely distributed throughout the world. The northern limit in Japan of the Japanese eel is the river Horobetsugawa, a little south of Erimo point, on the side of the Pacific Ocean, and the river Ishikari on the Japan Sea side. Once it was caught with a herring net near a river moUth in South Saghalien, but perhaps it was a group of drifters by an unusual change of ah ocean current. The distribution ofJapanese eel can be found out bY the haul of eel in various rivers in each district. - 31 -

As seen by the statistical data, the side of the • Pacific Ocean shows the larger eercatch, and especially along the coast of the river Tonegawa, the haul is the highest. Comparing that to the Pacific Ocean side, the Japan Sea side produces only about 9.3% of the eel haul in the Pacific Ocean coast. The haul in the area of Kyushu facing towards the Eastern Chinese Sea is larger than that in the wider coastal area along the Japan Sea. In the north of the Noto Peninsula along the Japan Sea coast, the haul is very small. It has been noted that there is a dramatical difference between the haul on the Japan Sea side and along the Pacific Ocean, and that . the haul decreases rapidly as the fishing site moves • north along either side of the Japanese Islands.

„In the Àsian .Continenti the_ael,is_not_found_on the east coast of Korea, that is, the Japan Sea side, but around the Strait of Korea and on the west side of Korea as northerly as the Gulf of Pechili, the eel are known to live. In south of Korea, the eel are found all along the Chinese Continent as far south as Tonkin of North Vietnam. It is also found in Hainan Island, Taiwan, and Okinawa Islands, but not at all in the Philippine Islands. In the Pacific Ocean, it is found in Ogasawara /15> Islands, Hachijo Island and Miyake Island but not in Saipan, Palau, Iwojima. Therefore, the southern limit appears to be near Hanoi, North Vietnam, the eastern limit, Ogasawara Islands, • wostern limit, an upper stream of the Yangtze River or the - 32 -

Yellow River, that is, the Central part of the Chinese Continent somewhere in Szechwan Province. 0-unagi or kanikui is the most commonly found eel in Japan, especially in the area where the Black Current washes the coast. Its northern limit is Cheju Island, the river mouth of Tonegawa and Tateyama, and its eastern limit is Ogasawara Islands in the Northern Pacific Ocean and Marcus Island (Minami Tori Shima) in the Southern Pacific Ocean. Its western - limit is Natal of the east coast of Africa and it is also the southern limit. In the major areas of habitat in Japan, the eel is commonly protected being designated as a natural monument. The major areas are Kabashima, Nishi-Hikan- county of Nagasaki-prefecture, Kaibu-town, Kaibu-county of

Tokushima-prefecture i Tnmidn Nishi-Mwr(1- , ^unty of Wakayama- prefecture and Jogaike, Izu of Shizuoka-prefecture among others. Distribution of the eel is deeply related to the sea current. Namely, the currents influential to the distri- bution of the Japanese eel are the Black Current, Tsushima Warm Current, and Chinese Coastal Current, and the Black Current is most strongly influential among them. 0-unagi is subjected to the effects of the Northern Seasonal Wind Current, Pacific Equatorial Current, Indian Ocean Southern Equatorial Current and both Pacific and Indian Equatorial Anticurrents. - 33 -

LIFE HISTORY OF THE EEL • .When the adult eel arrives at the middle layer of high temperature and high salt content ocean and finishes

laying e,zgs, the long spawning migration trip ends. This is also the time of death of the adult eel. The spawning ground of the Japanese eel (Anguilla

laponica) is north of lat. 20° N. and south of lat. 28° N. between the Okinawa Islands and Ogasawara Islands. The ground is a long oval shaped sea district surrounded by the afore- described islands and including the Okinawa Deep, North and

South Daito Islands and Lasa Island*. The spawning period of the eel appears to start at early spring and ending in the middle of the summer, that • is, .about 5 months. Tbis estimation is based on the appearance of very fine leptocephali within the spawning ground in February to July, but in other seasons, they have never been found. The eggs are laid and hatch in the same middle

layer, about 400 to 500 m of the depth, of the ocean. This

layer is characterized by the temperature 16 to 17 °C and the

salt content is higher than 35 o/oc, .and these conditions may be the ,best environmental factors for the adult eel and for hatching of the eggs.

(Fig. 4) /16

• Translator's Note: Transliterated, or Rasa Island. - 34-

One female adult eel lays about 7 to 13 million eggs at once. The eggs are suspended in the sea water without depositing at the bottom. The size of the egg is about 1.0 mm of diameter, and it hatches while being suspended in the sea. Because of its structure and characteristics, it undoubtedly hatches in the middle layer, and all those obscure informations leading us to the misconcept of the eel laying eggs at the ocean bottom or in the sea water as deep as 4,000 to 5,000 m are incorrect. It is assumed that the hatching takes place in a

relatively short period, perhaps . within 10 days after being laid, and probably after the 4th or 5th day. The smallest

fryl very soon after the egg hatched and still carrying the • yolk -saok, Is -about -G -mm long. The fry Immediately :ascends towards the surface layer of the ocean, and when it becomes as long as 7 to 15 mm, it is found frequently in the water as deep as 100 to 300 m. Later when it grows further, it approaches closer to the surface, about 30 m deep. It ascends much closer to the surface during the night, and thus it

remains ma 30 m deep layer during the day and ascending to

and upper layer 0 to 30 m deep during the night. While repeating this up and down motion, the fry disperses drifting to various direction being carried away by the surface current. The author and coworkers collected 19 leptocephali,

12.2 m to 23 mm long on the surface of the Okinawa Deep o • 121 57'E, 24° 32'N, during the-night of Feb. 12, 1961. - 35 -

While the eel remain as a , it has little resistance to the change of the environment, and it does not have any mobility, and consequently, if the surrounding conditions deteriorate, it dies away quickly. For this reason, the distribution of fry and subsequent fate to become an adult eel are to be limited to the are where the environmental factors are favorable to the fry. In the case of the European eel, the fry reach the European Continent in 3 years after hatching, and start to ascend a river. The rate of growth of the juvenile eel is, according to the measurement carried out in June throughout the period, 25 mm in the first year; 53 mm in the second year and 75 mm in the third year. It is a leptocephalus until the second year and a shirasu in the 3rd year and later. The leptocephalus circulates close to the shore /17 and steadily grows. The most remarkable changes of the body of the leptocephalus are development of the fins and teeth. The age of the leptocephalus can, therefore, be determined by the body size and the degree of the development of these organs. The juvenile Japanese eel starts ascending a river within 1 year after hatching. Just as it approaches the coast, it undergoes matamorphosis to a shirasu eel, and this takes *place during the fall. The metamorphosis processes include dehydration of the tissues of the leptocephalus, chani;ing its body shape from a flat willow leaf to a quasi- • cjlinder, loosin the length and weiht, shortening of the - 36-

intestines, and changing the larval teeth to permanent ones. • The fresh shirasu-eel l after the metamorphosis, stay in the mud or under stones and rockes at the sea bottom, near the coast and awaits the time when the river water warms up. During the winter, the water temperature of a river is usually lower than the water temperature of the coastal sea water, and therefore, warming up of river water is diappearance of the temperature difference between rivers and the coastal sea water, The Japanese eel start to ascend a river from the middle of October ending late in May, and the peak season is February and March. It takes place only during the night, starting at the sunset. The eel aré carried away upstream by high tide, and settle in a river before dawn. The highest activity of the ascension takes place within 3 hours after the sunset. The color of precipitated pigment becomes darker during this period. The krokko or dakko increases its ratio in the mixture of shirasu-unagi and krokko . by May, and in June, biri can also be seen. Usually krokko keep ascending until the end of July, and grow to about 15 cm in length. By August, it stops the movement but mesokko still ascend till almost the middle of autumn. When these small eels, shirasu-unagi, krokko. and mesokko, start to ascend a river, they keep moving upstream whatever obstacles they meet in their way upstream. They feed on shrimps, crabs, shell fish, small fish and other foods. If there is a little moisture, and a small. :,-,i;rean of water, whether they are in the field .or farm land, -37-

they keep moving. Even . a cliff, they can get over by repeating • again and again. The eel can even climb up Niagara Falls to reach the Lake Erie. Anybody can be convinced of their fantastic fighting spirit of ascending rivers, when he actually sees the way they swim up the stream to get up a dam built across a mountain river for hydro-electricity. The old saying that "a yam converts itself to an eel" perhaps originates from the fact that the ascending eel does reach anywhere even away from the stream. In fact many can cover short distances over land on a wet evening. It isindeed a grand sight to see an enormous number of eel swim upstream from a fiver mouth. As the ascending eel advance in mass formation aggregating very tightly, even the river water changes the color. When the eel settles in small rivers, lake, swamp, ditch, creek or lagoon, it hides in a hole, under stones or rocks, or in mud during the daytime, and comes out during the night to feed. From the spring to the fall, it grows quite well and most rapidly early in the fall. The natural foods of the eel are shell fish, insect, small fish, worm, crab, frog, shrimp and others. When the water temperature goes down /18 lower than 15°C, it looses appetite, and it does not feed if the temperature is as low as 10°C. Although it feeds more

when temperature rises higher, if it is 28°C or above, it looses appetite. During the winter, it does not feed-and stay in mud. Even during the winter, however, if the water tempera-

tre i- oes up above 10°C discontinuously, then it comes out of

eer,, - 38 - the mud and seeks food. The eel that lives in a river, lake and pond still holds its built-in nature of ascending a river, but when the temperature starts to go down in the middle of September, ome of the eels already settled in the river start to swim down the stream. This rheotaxis phenomenon has been explained by the migration of eel towards warmer water, as the upper stream holds colder water than the lower stream. This rheotoxis phenomenon is quite often observed when the wind and rain are strong and heavy. By taking this migratory action, the eel can survive the winter more easily in warmer water. Thus the male eel matures in 3 or 4 years and the female eel about 1 year behind the growth of the male. When the eel becomes mature, it starts to exhibit the nupital color, that is bluish black on the back, pale golden yellow on the side, pale pink on the abdomen, and gold at the base of the Pelvic fins. The nupital color develops at the end of September towards the end of October, and the mature eel swim down the stream towards a river mouth and to the ocean. The descending eel is called kudari-unagi (descending-eel) and it is seen earlier in northern areas than in the southern areas. The fishermen of Fukuda area of Iwata-county, Shizuoka-prefecture, engaged in catching the natural eel, insist that "an ayu fish (sweet fish) makes love at a second rapid but an eel does it at the first rapid or at the river mouth" and that they often see the "setsuke" phenomenon of eel

'r.7c7:177' - 39 -

near the river mouth where reeds grow thick, during the period • between the middle of September and early in November. This "setsuke" phenomenon usually signifies active swimming action of one female fish and several males chasing her at a spawning site and this action is accompanied by the female's spawning. However, in the case of the afore-described observations by the Fukuda fishermen, the eel involved is not sexually mature. In any case, however, the mature but not sexually mature male and female eels descend the stream in à large group. Just before they start to descend towards the sea, they stop feeding and never feed. As a result, their digestive organs start to deteriorate. Thus, the deàcending eel can be caught in a mass with a net or yana (weir) but never with a bait and • hook. There is a new fishing technique developed after the war. It is called "saba-tobi-tsuri"* fishing, and it is performed in the East Chinese Sea off the coast of Okinawa. The fishermen engaged use a scoop net or a hook to catch a large number of descending eel swimming in a group of several eels during the night. All the eels caught by this method are known to have no food residue in their digestive organs. According to the results reported by foreign scholars, the descending eel swim 8 to 32 miles per day, as determined by a tag methdd. However, this speed of migration increases to 30 to 60 miles per day when the envirônmental factors are • favorable to the descendin.s eel, * Translator's Note: Literally mackerel-jumping-hook. - kO -

4. FACTORS COETRIBUTING TO TEE GROWTH OF THE EEL CULTURING

BUSInSS /19

• Six factors, human element, culture stock, feed, environment, diseases, and business administration may be cited as essential factors to be taken into consideration to carry out a successful eel culturing business. The most important is the perfectly balanced human element and only -after other elements are well adjusted to meet the requirement, this business can be operated successfully. Human Element: This factor is of course the most important in starting out any enterprise and to develop it successfully. The eel are like a human infant who.cannot speak to express his feeling, and since the eel is completely expressionless, a tender of an eel pond has to know the physiology and ecology of the eel very well and treat the eel at the eel's standpoint. This is true not only for the eel pond tender but also for anybody who is engaged to look after . However skillful in business administration or in other techniques a man may be, if he is not kind enough to the eel, he cannot be successful in this business. The required characters of a man who is engaged in this business are to be able to devote his love to the eel and to have enthusiasm of concentrating on the eel culture. :*î! must also be a skilled technician who can increase the production but at the same time, he must be capable of taking notes of b is observations, and to analyze the current situation of the eel culture business.

mmmr.7_immmu, - 41 -

11 a technologist of culturing eel, he must be equipped with a willingness of always carrying out observations, experimentations, and improvement. Since this business involves a number of corporative activities, such as joint purchase of feed, marketing of grown up eel, and joint purchase of culture stock. It is highly desirable to develop the business in a wider area through a corporation system or some other kind of group organization. Therefore it is highly important that

the business man in the eel culture posseses either a leader-

ship capability or a cooperative spirit. • The pond guard should have a strong sense of responsibility and a keen eye of observation. Culture Stock: This factor is as important as the feed for

the fry. Before the war, the production cost included 40.6%

of the cost of purchasing fry and 39.4% of the feed cost, but the ratio has changed particularly lately. The feed cost now

takes up about 49% of the cost of production, and the cost of

fry is between 20 and 30%, varying from year to year. However, as seen by the data accumulated since

1910, the price of grown up eel has been controlled by the cost of the fry, and the quantity of fry available for the

. eel culture is the decisive factor controlling the scale of the eel culturing business and its production quantity.

Therefore, the buality of available culture stock strongly

influences the production quantity, and cuality and price of the product. Therefore, it is very important to secure a - 112 - required amount of the fry with guaranteed quality to be truly successful in the eel culturing business. As the fry for the eel culture, the following three different kinds are available; 1) shirasu-unagi, 2) yobiri or yochu, prepared by culturing shirasu-unagi, /20 and 3) natural juvenile eel captured in rivers, lakes, swamps, ponds, lagoons, and various other natural sources. The fry in the last category are at least one year old after leaving the sea, and it is called natural starting material, and its size varies between 15 and 25 cm and 5 to 20 g. The fry of the former two classes, 1) and 2), have been available from another independent business source that specializes ln producing the culture stock from shirasu-unagi. This business also appears to be quite profitable. Sabhi* fry is introduced into a culture pond anytime after middle of May or early in June, in order to readjust the fish density in the pond from which some grown up eel are taken out for marketing. The quantity of this addition is determined by the capacity of the pond, the size of the eel remaining in the pond and that of the sashi to be introduced into the pond. Eashi may be any of yo-biri or yo-chu cultured from shirasu- unagi or natural fry at various stages of growth. Feed: Feed is also one of the most important factors to Govern the success of eel-culturing business. In recent years, the feed cost is taking up about 70 to 30% of the production

Translator's Uote: Se Chapter 2, section 1). cost, and therefore, it is important to carefully examine the quality of the feed and to improve . feeding conditions. Feeding fast growing eels with a larger quantity of high quality feed is of course the key factor in increasing the body weight of the eel and this can be achieved when the environmental factors are adjusted suitable for the culturing. In the old days, fresh or frozen fish meat has been used as feed but lately, mixture feed is more commonly used. In fact about 90% or more of the eel feed is a prepared ready-to-feed mixture feed. Environment: In order to let the fry maintain good appetite and grow rapidly in good health, thé environmental conditions of the culture pond must be excellent. The environmental conditionsto be thoroughly examined are water quality, bottom soil quality, location and shape of the pond. When eel is cultured in a pond at a high density, corps of animal and vegetable plankters, residue of excess feed, and excrements of eel deposit at the pond bottom in a large quantity making the living of the eel very uncomfortable, consequently reducing its feed consumption. At the same time, when these organic residues and wastes at the pond bottom are oxidized, a large quantity of oxygen dissolved in the water is consumed. This has direct detrimental effects on the respiration of the eel. Therefore, it is necessary to retain the dissolved oxygen concentration at a high level, .so that the eel in the pond • can maintain good appetite, living under confortable environment,

n7,71,7rn.41rrementersznere7,- uerebrene - 44-

When the organic residues precipitate at the bottom in a large quantity, the bottom soil tends to show an acidic reaction, and it is preferable to retain the neutral conditions at all times. If vegetable plankters die in a mass within a short period, then animal plankters multiply quickly and in a large quantity. This causes rapid change of the water color from greenish violet to brown, and the eel suffers from difficult respiration, and oftentimes a large quantity of the eel perishes. This phenomenon is called mizugawari*. The changing water has to be detected in advance and must be prevented quickly. . Bringing up the cultured eel under more comfortable /21 r1(1 “:4 (-)n,s may he nchievP.(1 oni.y by cr%nr.entrrl efforts trN forcast any deterioration of the environmental conditions and quickly correct the factors causing the change. Only highly qualified eel culture technologists may be able to achieve the goal. Diseases: When pond culture ofthe eel is done at a higher density of the eel in a pond, it forces the -eel to live under unnatural conditions far different from its living condition in nature. Consequently the eel becomes more liable to • disease. The disease incidence rate tends to increase in proportion to the degree of artificial alteration of the

* Translator's Lote: Literally changing water. 45

natural environment. • Types of disease that are found in the eel culturing business are numerous, including diseases caused by parasites on the skin and those of the internal organs. Certain diseases cause serious damages to the business, and some are quite seriously contageous with no established methods of prevention and cure, while others occur very frequently but, because of well experienced methods of prevention and remedy, do not cause any serious damage. The kinds of disease which occur frequently vary from year to year, and from one area to another. If the disease vas found contageous, fish Contracting it should be quickly isolated, and dead fish must be buried or burned, and • should never be left in or near the water way to and from the pond. Diseased eel may be accurately detected only after experience of many years, but generally speaking, its body color darkens considerably; it stays away from the group swimming along; it may repeat stop in, stand still and rushing about wildly; or it rubs its body against the pond wall. When these or other unusual movements are seen, the eel that does it should be taken out from the pond, and examined carefully. Business Administration: In order to obtain the largest profit with the smallest amount of effort at a minimum cost, not only the highest ;rade of technical skills but also superb talent in the business accompanied by excellent sales technique, iS reired.

7M7,75.77=7=7:Ue7.71 46 11.10M

5. CULTURE ÈOCK 110 1) Shirasu-Unagi (1) Ecology before ascending river Juvenile eel become a leptocephalus poon after hatching, and float up to an upDer layer of the ocean from the 400 to 500 m deep middle layer. When it becomes 7 to 15 mm long, it lives in a 100 to 300 m deep layer, and further when it grows larger, it moves to the surface layer between 0 and 30 m, staying deeper during thè day and floating up towards the surface at night. While gradually shifting towards the surface layer, it drifts away from the spawning area where it was born, and approaches closer te. the coast. At the shore, it undergoes the metamorphosis at the bottom near the shore, and becomes a shirasu-unaei, Immediately after this metamor- phosis, it starts the motion of ascending rivers, but it remains in rivers close to the river mouth hiding in the bottom mud, behind rocks and stones, among weeds or other /22 objects, and wait for the temperature rise of river water from 8 to 10°C, which is suitable for ascending. The content of its digestive organs is full of detraitus*, and perhaps its feeding activity is rather inactive but as the water temperature rises, it starts to catch and eat small animals. At around the same time, its body color darkens as black piments start to precipitate, and the back surface turns black in about 1 week at 11 °C of water temperature.

* TransiaLor's 1àybe: Transliterated.

■■■■ m,fflummaumtirnme This is called kurokko. Leptocephalus shows thigmotaxis, • that is, it avoids physical contact with objects, and keeps swimming in water, but after the metamorphosis, it starts to require a hiding place, becoming fond of contacting physical objects. Near the coast, it shows nocturnal characteristics, and ascends river only at night. During the day, it stays still in the bottom mud of the river, avoiding the light. This has been known for many years and also proven by observa- tion in lakes or by laboratory experiments. The property has been well utilized at the time when shirasu-unagi is trained for feeding. Namely, a pond holding shirasu-unagi is darkened before starting feeding during the daytime. This proves that the eel has an inborn property of phototaxis. However, in as well as in this country, lamps are used to catch shirasu-unagi, but in this case, the lamps are not intefided to collect shirasu-unagi by its heliotropism character. If it were for the heliotropic nature of the eel or shirasu- unagi, the effect of lighting should be proportional to the amount of fish caught. In reality, however, if strong lamps are used, the haul decreases. In Italy, there has been a very effective method of capturing shirasu-unagi since ancient times. The method is to fill up a shallow part of the bay with fresh water and attract a large quantity of shirasu-unagi. This method is • based on the nature of shirasu-unagi moving towards fresh water. -48 -

Shirasu-unagi can feel fresh water even 10 miles away in the ocean, and its movement towards fresh water in rivers, inlets, or lagoons is identical to the movement along the direction towards the lower salt concentrations. This has been explained as a result of shrinkage of its body by excretion of thyroxine at the metamorphosis, accompanied by strong dehydration, both of which result in concentration of body fluides. The old saying "a yam turns itself to an eel" is to symbolize the • strong river-ascending nature of eel, and this nature is more strongly exhibited while shirasu-unagi are .younger. This rheotropism is also said to be deeply related to the amount of thyroxine excreted. (2) Timing of Ascension For many years, it has been believed that the eel starts ascending river in early spring to late spring, but it is now confirmed that the starting period is late fall or early winter. It was confirmed by actual observation that the eel ascended rivers in Shizuoka-prefecture in the first decade of October, and also in the river Kawauchi of Kawauchi- city, Kagoshima-prefecture on Oct.. 27, 1961. The season that the eel ascends river, therefore, is a long 7 to 8 month period, from October to the end of May. In this period, however, the temperatures along the coast and in rivers vary considerably from year to year and depending on the locality. When the author studied the effects of environmental factors and the timing of the ascension on the - quntity of the ascending eel, in rivers around Yoshida, /23 Narahara-county of Shizuoka-prefecture, the following results were obtained. A. Even when the environmental factors are poor, and particu- larly the water temperature which is so low that only a small quantity of eel ascends the rivers, fairly large groups of eel ascend rivers, breaking the usually monotonous, small flow of ascending eel. This sudden, large quantity of ascending eel is characterized by its irregularity. This occurs at the beginning period of ascension (from the middle of October to the end of December). B. Apparently because of rather complicated combinations of various environmental factors, althdugh the ascension quantity steadily increases and the quantity finally reaches the maximum throzhr,ut the ascension neriod„ the day-to-day Quantities of ascending eels varies considerably - peak ascension period (the end of January to the beginning of March). C. The variance in the ascending quantity becomes less after the peak period or late in the peak period (the middle of March to the beginning of April). D. Later, the environmental factors become less effective in controlling the ascending quantity, and the quantity gradually decreases but appearance ratio of kurokko becomes larger towards the end of ascension period (the middle of April to the beginning of May). E. The ascending eel becomes seriously influenced by ebb and flow and by the time of risinc tide among other environmental factors, and in ueneral, the ascendin[..; quantity decreases at the terminal period (the beginniïkof May to the end of May). - 50 -

(3) Environmental Factors Controlling the Ascension Quantity The environmental factors which influence the ascending quantity of shirasu-unagi are water temperature, tide, time of rising tide, time of sunset, height of tide, atmospheric temperature, humidity, atmospheric pressure, wind velocity, direction of wind and rain or shin and.so forth. Water Temperature: At the beginning of the ascension period, the water temperature is a critical factor. It is important that, in this period, water temperature in the river and sea water temperature approach close together. If the river water temperature is below 8 to 10 °C, the ascension usually does not take place but if it varies above and below the same temperature range of 8 and 10°C, the water temperature is the most eritical -.factor, if not the only one, but when the temperature is stabilized above the temperature range of 8 to 100 , then it is no longer an important factor, other factors becoming more critical. It is usually the middle of March that the temperature stabilizes above the critical temperature range of 8 to 10°C in Narahara-county of Shizuoka-prefecture. The period that the temperature stabilizes is also the peak ascending period of the eel in the area. If the temperature lowers at a rate of 100 per 3 hours, then shirasu-unagi can survive for a while, even if it is in near freezing water at 0.8 oC I but if the water tempera- ture lowers at the rate of 1°C per 25 minutes it falls in a syncoptic state.

" '""" Although the Japanese eel participates in the • river-ascending motion only if the temperature is above the o range between 6 and 11 C I the European eels are supposed to be most active in ascending rivers when the water temperature is between 2 and 10°C. Tide: When shirasu-unagi enters into rivers from the coastal sea, it is carried into the river by a rising tide. Therefore, the initial motion of shirasu-unagi is deeply related to the ebb and flow. When the tide rising progresses, the ascension also approaches the peak activity and when the tide starts to fall, the ascension quantity starts to decrease. Even if the water temperature is ideal, the ascension cannot take place in an evening when the low tide occurs within two to three

hnuD. .mfter> sunset It iS nnly in an PvPning whPn the bigh tide takes place within two, three hours of sunset that the ascension occurs. If the high tide takes place immediately after sunset, the quantity of the ascension is also the /24- largest. Besides, if the full tide level is higher, then the quantity of ascension is also larger. If the full tide level is low, the ascension quantity is either nul or very little. If therais no ascension taking place evenwhen all the conditions of the ascension are excellent, it is usually. because of low level of the full tide. As to the relationship between the quantity of the ascension and current, it has been prbven that the ascension takes place in larP;er quantity in an inland bay where there is the effects of the Black Current are strong.

;,eett4WT.Menet.biliarr..n."'"' - 52 -

The results of studies carried out in rivers of ::a-'abara-countY of Shizuoka-prefecture, the ascension starts very soon after sunset, and the ascension quantity gradually increases, reaching the maximal quantity within 1 to 3 hours after sunset, and even within this same period, the peak ascension time varies depending on the full tide hour and cloudiness of the sky at sunset. The ascension is completed for the day in two and a half hours to five and a half hours after sunset. As observed in the Lake Hamanako, the ascension takes place in a period between 1 hour after sunset and 1 hour before sunrise, the peak ascension taking Place when the full tide starts and 2 hours after the start of full tide.. The ascending • eel is active in the movement until ernund 1 1 and when it is close to dawn, it starts to hide in the bottom mud. The quantity of the ascending el and the period in which the ascension continues vary depending on flow rates and width and depth of rivers. The ascending eel usually hides in sand or mud at the river bottom or among weeds,.in shade of rocks and other objects in the river, and resumes the ascension at . sonset. The ascension activity decrease at midnight, and towards . dawn, it starts the hiding activity. Yind Velocity and Direction: In the Lake Hamanako, when the L>lows towards west, more ascending eel can be fished on the east coast, although this tendency is quite unrelated to • the aL?,cension itself. As far as the wind velocity is concerned, - 53 - the ascension quantity is larger when there is a light wind, 1 or 2 in the wind scale than when there is no wind, but the stronger wind always decreases the ascension quantity. (4) Size of Eel at the Ascension Shirasu-unagi just completed the metamorphosis near the coast continues some other physical changes of its body shape. The major changes are increase of body width, lowering of body height and shortening of body length, and therefore, these may be considered to be a part of the continuing metamor- phosis. The size of shirasu-unagi before completion of the body pigmentation is 64.4 mm at the largest and 52.0 mm at the shortest. Average body length in rivers in one and the same area is largest at the beginning of the ascension period, and it gradually becomes smaller as the time passes during the period. (Table 2) This decrease in body length occurs as a result /25 of increasing ratio of krokko in a mixture of shirasu and krokko towards the later period of the ascension. When the average body length of shirasu and that of krokko captured on the same day were compared, the former was 57.921 ± 0.061 mm and the latter was 57.068 ± 0.056 mm, and the length of krokko was shorter as the body shrinks when the pigmentation occurs. - 54 -

There also is a difference in the size of shirasu due to the location difference. There is a tendency that the ones captured in the area where the effect of the Black Current is strongl are usually larger, and also because of the relation of the body length to the water temperature, the average body length of shirasu varies from year to year. When the temperatures of water in rivers or coastal sea water are low, the size of shirasu-unagi tends to be larger. This means that, if the water temperature of the year can be fore- casted by a long term variation of coastal water temperature or by other means, the timing of ascension of shirasu-unagi could be predicted well in advance.' (5) Annual . Variation of the Quantity of Ascending Eel and its PArindirity Fluctuation of the ascention quantity is indeed a frustrating experience that every eel culture businessman has to tolerate. Annual change of the ascending shirasu quantity has been already recorded but the data available is not quite satisfactory for statistical analysis. Therefore, the factors in controlling the good and bad haul of the ascending shirasu from year to year are still unknown, and consequently one of the most urgent problems to be solved for the eel culturing business, that is, prediction of shirasu haul for the coming year, still remains untouched. According to fragmentary recorded data at the end of March in 1921, a large quantity, about 60 Kg per fisherman,

,:1_-,2;:l.reeeereeeeQubeeellmwel pl,WeVAYMCnWe. - 55 - of shirasu was cauert in down stream of the river Toyokawa of Toyohashi-city in one night. As the demand of shirasu-unagi increased, the haul in Shizuoka-prefecture was 11,308.1 Kg (number of personnel 1,619, not including the transferred quantity 3,750 Kg from other prefectures), which was the amount permitted by the Fisheries Control Board, in 1937, and 11,756.3 Kg in 1938. In 1950, when the eel culturing business reopened after the war, 375 Kg was caught and this was sufficient to cover the demand for the year, and as the demand increased later, the haul also increased, as 2,250 Kg in 1951, and 4,500 Kg in 1952. However, in 1953, the haul was only 1,125 Kg against the demand, 9,375 Kg, and in 1954, the haul was even smaller than this. In the following year, the haul was excellent and after this year,there was no particular rise and down in the annual haul and the business was carried on rather smoothly for several years until 1962. In this year, the haul was the poorest over recorded since the eel culturing business started, and every businessman in this trade ran around throughout the country seeking shirasu-unagi, without success. In the following year, 1963, however, the haul was the best in the history of the eel culture. The price of shirasu-unagi also fluctuated tremendously depending on the haul. For example, in 1962, shirasu called for 70,000 yen for 5.75 Kg but in 1963, the price started at 40,000 yen per

3.75 Kg and went down to 5,000 yen per 3.75 Kg in March. In 194, the haul was again poor and the price was 40,000 yen - 56 -

per 1 g, and in later years the price more or less settled • at a constant level. In 1969, the haul was extremely poor /26 and the price was 100,000 yen per Kg. . (Fig. 5 and 6) In many European countries, the statistical data on eel is available in reliable accuracy. The annual haul of shirasu-unagi in Italy between 1922 and 1933 varies every alternate year, a big catch in every odd numbered year and a poor catch in every even numbered year, and steadily increasing for ,a 3 year oeriod and decreasing for the following 3 year period, that is, a periodicity of 6 years. In France, however, the odd year shows a poor catch and 'the even year a big catch, as shown by the data in 1929 to 1934 and this is opposite to • the tendency found in Italy. Since the Atlantic eel spends about 3 years from the spawning ground to the coast, and therefore its haul is greatly influenced by the conditions of the ocean. Fluctuation in the annual haul of European and - Danish shirasu-unagi resembles very closely to the annual /27 change of the salt content of the coastal . sea water 10 years before the each corresponding year, and the year of rich haul corresponds to the year of high salt content. Since the haul of shirasu-unagi is directly related to the production quantity of the eel culturing business in this country, the cause of titJ periodicity of the haul and its irreiplarity must be studiud in detail. .:?ecarding the cause of yearly or monthly fluctuation of imul of shirasu-unaÈ;i, the decreasinu natural source of eel

' I r - 57 -

and appearance of icebergs in the Arctic Ocean,among other • theories, have been proposed. The decrease of natural eel source is proposed based on the over-harvesting of shirasu- unaui by reckless catch, over-consumption of eel and pollution of coastal waters. In analogy to the theory that European eel lias its origin in American eel, the Japanese eel is considered to be supplied by the eel source originated from the Chinese and Korean eels in addition to the Japanese eel. $o far as the eel source in the Chinese Continent is kept as it has been, there appears to be no immediate danger of disappearing of the eel fry needed for the eel culturing business. Position of appearance of icebergs and their size and other conditions of the sea, especially the temperature of the coastal water are quite important factors that determine the haul of shirasu-unagi. In the Lake Hamanako, if the average temperature of coastal water in December is 10.5 °C or lower, the shirasu-unagi haul of the year is poor, and if it is higher than 11 oC, the haul in the months of January to arch is good. The average water temperature in February and el,t. haul are inversely Droportional. As a countermeasure of the poor haul, import of shirasu-unagi from foreign countries and artificial spawning, and cultivation of eel fry have been planned. The lattur rethod involves academically interesting problems relr:ted to acceleration of maturation of the eel, artificial • irritaLion and others, and these orohlems have been solved

72M-77.7,i7eM11,17MM.777I - 58 - mostly at the level of laboratory operation but for the indus- tial purpose, not very much should be expected too soon. In orde .,- to solve the problems related to forecasting the shirasu haul, a more detailed basic study is needed in analyzing the spawning ground, the conditions of the sea from the spawning f:round to the rivers, and the ecology of the juvenile eel in the sea. (6) uality of Fry There are two kinds of eel, one is wide head type and the other the narrow head type, and the two different types exist already at the stage of shirasu-eel. In Germany, the wide head eel has been considered to be tasty and expensive while the narrow head eel is cheap because it has a smaller amount of meat ; The fat content of the wide head type eel is 12% while that of the narrow head eel is 27%, and the weight of the heart is also larger in the wi'de head eel. This difference is caused by the difference in growth rates and, mobility of the two types of eel. Namely, the wide head eel is quite active and moves fast, and it lives on smaller fish and other animal food and grows to a larger .5i:e than the narrow head eel, living in shallower water. On the other hand, the narrow head eel is polyphagous and lives mainly on invertebrate animals and grows to a smaller size tL::n the wide head eel, living mainly in deep fresh water not far from the sea.

( ig. 7 ) - 59 -

As already described in a previous chapter, shirasu-unagi which Grows very well has the short, round and thick forehead with the wide forehead angle, while the poorly rowing eel has the long, sharp, and thin forehead with the narrower forehead angle than that of the wide head eel. There have been many theories proposed as to the difference between these two types. For example, one theory assumes that the two different types are actually different species., and another assumes that the difference is that of the sex, male and female, and numerous other theories are that the wide head eel is sterile female fish that does not run down the stream to the sea for Spawning while the narrow head eel is either male or female fish which can lay eggs, and that the two types are two extreme morpholozical charac- teristics, not based on the sexual difference, and head of the wide head eel becomes narrower and thicker* as it grows. The author proposed previously that although the difference was not directly representing the difference of the sex, the wide head eel belonged to the female-type and the narrow head eel to the male-type eel, because as far as the morphological cllaracteristics were concerned, there were a number of other intermediate types which had been found and perhaps the sex- determination took place at initial stages of growth of juvenile eel. As the development of its'genital gland progresses, • the eel Goes throuh the following four diffèrent stages; * Translator's Note: Thinner? it is neutral while its body length is between 6 and 9 cm, • immature feale at the size between 10 and 14 cm, hermaphroditic at the size between 18 and 30 cm and dioecious at the size larer than 30 cm. It is evident, therefore, that the conver- sion of the sex takes place in the early stages of growth of the eel. • This conversion of sex is often observed in many lower classes of animals. For example, the Sex conversion of many species of fish including gilthead has been verified by laboratory experiments. According to some foreign researchers, there are three different groups'of shirasu-unagi ascending rivers (as it is about 2 years older than Japanese shirasu- unaji ascending rivers, it is much larger), and the group of smaller fish consists of male, the larger fish, female, and the intermediate, premature female. They also proved that if the larger fish is cultured under poor conditions, it converts itself to male, and the small fish to female if fed well under good conditions, that is to say, the conversion of sex can occur depending on the environmental factors. (Fig. 8) In summary, the well growing shirasu belongs to the wide head type and the poorly growing one is the narrow head type. The female type eel is, therefore, the wide head Lype and the male type eel is the narrow head type, and this difference already appears while it iS shirasu-unagi. Depending on the conditions of feedinL; and culturing, however, it is ci.;nverted to, the other one of the two sexes. Generally

„ . „ . . .• _ . - 61 -

speaking, the Growth rate of the female eel is better than • that of the male eel. Even.if the eel is at a size of 40 to 95 cm, the eel of the wide head type grows about 2 years faster than the narrow head eel, and its body weight is larger than that of the narrow head eel. Since the genital organ of the eel is basically the same as that of the female, the better growing eel is the wide head type eel. Therefore, in order to control the head type by artificial methods, the /29 best approach is to control the conversion of the sexuality by an artificial method. Although this has not been accomplished, it might be useful to administrate female hormones as a feed additive when shirasu-unagi are firdt trained for feeding. • (7) Growth Rate Usually, shirasu-unaei start to feed when trie water temperature is between 12 and 13. Therefore, the feeding is done from March or April«and stopped at the end of November or the beginning of December. Thus the period in which the fry really grow is about 8 or 9 months. The maximal growth . rate during this period is shown in table 3. Since the growth curve of living creatures can be shown by a sigmoid curve, - taking the origin of a curve at the initial size of shirasu- unagi, and the final growth point at the end of the feeding period as the maximal point, a general growth curve during the period can be obtained (Ifig. 9). (Fig. 9) • (Table 3) /30 - 62 -

It invariably occurs that when a large number of fry are raised, a group of fry grow at an excellent growth rate, and this group of fry are called "tobi"*.. When "tobi" are separated and fed under ideal conditions, the so-called sigmoid curve can be obtained. On the other hand, there is a group of fry which grow only at a minimal growth rate. In the case of shirasu-unagi, the growth is only slightly over the average size of shirasu. When growth rates of all the fry are averaged, it is much lower than what is shown by the sigmbid curve. Therefore, the aim of improving the culture method is to increase the ratio of well developing fry to the total number of fry. (8) Resource In some -years recently, theliaul of -shirasu-unagi had been particularly low, and yet the demand of shirasu increased so much that suppliers could not fill the orders they received. As a result, the older businessmen in this enterprise started to suppress the new corners entering into the competition. As a measure to improve the ever decreasing hauls of shirasu-unagi in recent years, the traders in Shizuoka- prefecture release about 6 tons of mature eel to the sea every year, ab an aid to the natural spawning. This is done in fear that the large, recent consumption, about 22,000 tons per year, decreased the natural resource of the Japanese eel reducing the eel reproduction quantity.

MOM■■edeeel.....melm■ Mmai ■ adinemamemmemme■lblem.M. O * Translator's Note: Literally "to jump". -6 -

Dtstribution of the Japanese eel is in a rather wide area, and the centre of the distribution is estimated to be in the Chinese Continent as judged by the quantity of eel living in the total area of the distribution. The Japanese eel is, however, consumed mainly in Japan, and in China, Korea and North Vietnam, it is used as an elixir of.life rather than as a food. In China, about 60% of the total haul of fisheries product is the fresh water fish, but the eel is not even listed . in a statistical data sheet. Therefore, the natural resource of eel is still kept intact in the Chinese Continent. The eel culturing business may be considered as one way of preserv- ing the eel resource because the business is based on capturing the eel while it is at a juvenile stage, raising it to adult eel under protected condition, and using the finished product, the cultured eel for food, instead of leaving the juvenile eel exposed to possible harmful environmental conditions such as polluted rivers and lakes. Furthermore, it is considered that the annual consumption of the in Japan'is not much different from the mortality due to the'natural cause. Therefore, based on this standpoint, the poor catch of shirasu- unagi experienced is perhaps not the result of decreasing eel resource. Distribution of freshly hatched eel is governed by a current in the ocean, and therefore, even if the haul of shirasu-unai is poor in one district, it can be excellent in the other district of the wide area.of distribution. This sort of irre:7,ular distribution could occur easily .because of - 64 -

chan i s of the conditions of the odean, including the spawning ,round and the wide area of distribution of the fry. In fact the reverse alternate hauls of good and poor in Italy and in 'rance have.been best explained by the effect of the current. This country, which extends from south-west to north-east, with geographically complicated coastal lines, is under the strong influence of the Black Current.' The Black Current is the one that carries the juvenile eel to Japanese Islands and therefore the actual distribution of the eel on the coastal line is probably very uneven. Therefore, the haul /31 of shirasu-unagi should be controlled and regulated throughout the country. Besides, the regulation of import and export of shirasu-unagi should be done at an international view point so that the world distribution and resource of the eel remains under control. As examined of the genital gland of the eel, the e.el running down the stream to the sea has between 7,200,000 and 12,700,000 eggs in its ovary. The mature female eel lays the whole batch of eggs at once. Although the eggs hatch at a very high rate, it is very well known that the larger in quantity the eggs are laid, the smaller the chance that the eggs produce full-grown adult fish is. During the period in which these eggs hatch, and the 1ocephalus approach the shore and undergo the metamorphosis Lo shirasu-unagi, a large number of the juvenile eel must be exhausted due to various causes. In recent years, water O 65 pollution in rivers by exhaust from plants and cities is becoming quite serious, and the use of agricultural chemicals is also an additional factor of pollution. In this respect, the eel culturing business may be considered to be a way of protecting the eel. As seen clearly from what has been described in the above sections, releasing the mature, cultured eel to the ocean is not only practical at a stand point of conserving the natural resource but also a morally important obligation of every businessman in this trade. This author believes that it is also to be considered.as a thanksgiving ceremony of everybody in this trade who so heavily depends on the natural resource for their living and for their business. (9) Fishing Method Since the fry has to be captured without physidal injury, no all the existing fishing methods could be applied. The shirasu fishing usually is done in a small scale, and the tools for that are also quite simple. In Shizuoka-prefecture, a cast-net or a triangular hand net called "buttai" is used. The latter is constructed with one side of the triangular net open without a frame and two sides held by frames which join at one vertex which is fixed to a handle. In many areas, a cast-net is used. Its size varies considerably ',Alt must be suitable in operating during the night at quite low temperatures. The lamps must be Selected so that the intensity of the liL:ht is just enouÉh to confirm a group of el at niL;ht. The light ha L3 no effect in attracting eel, and -66 -

on the contrary, it expells the eel especially if the water temperature is high. The shirasu-unagi thus captured are placed into a container one catch after another. The container used is a wooden rectangular box, usuallY 35 cm long, 15 cm wide and 5 cm deep. On the central part of two sides, small mesh, metal wire nets are placed to let water flow through Quite freely. Some fishermen prefer to place the nets on 3 or 4 sides. A box of this size can accommodate 1.8 to 2.0 Kg of shirasu-unagi, and in some cases, a bottom and sides are made of ,the same fine mesh metal net in a cylinder. When more than 4 Kg of shirasu haul is expected for a day, a common eel busket for transporting adult eel can be used more conven- iently by placing-a piece .of •cotton,cloth .inside the busket bottom. One such busket can hold about 4 to 7 Kg of shirasu. /32 (Fig. 10) When a massive haul of shirasu-unagi has to be executed, a fixed net called an eel-bag-net* may be used more

conveniently. The net is commonly used in areas close to the Lake Hamanako or the river Tonegawa. The net consists of two wings and a bag, and fixed

at a centre of the river, cutting the water flow across the river with a bundle of bamboo tubes., wood stakes and others, and shirasu swim into•the net with the water flow. The size

of the net varies depending on the width of the river. The • net should be placed at a oosition àlere the water depth is about

* Translator's Note: Transliterated. - 67 -

two thirds of the mouth of the net, and the flow of the river should not be too strons. During the fishing period, when shirasu-unagi are ascending, the tail part of the bag net is lifted every half an hour or 1 hour and the haul is transferred to a container. In Ibaraki-prefecture, not only the net of this type but also scoop nets of various kinds are used for small scale fishing. Hauls with a bag net vary from day to day but the largest catch per day recorded is 48.8 Kg and if the ascension is not active, the haul could be less than 1 Kg, averaging 10.7 Kg per day. Storage in a Pound Net and Transportation: The hauled shirasu is handed to_a whole.sale ,dealer imme.diatsoly or on the next day. The fish are placed in a bamboo busket with about 40 cm diameter. About 10 buskets are placed one on top of another, and water is run through the top for about a one day period. The water used for this is fresh water pumped from the ground and the temperature is about 16°C. During this storage, about 10 to 20 of the fish die. From the wholesale dealer, shirasu are transported by a truck to eel culture ponds. About 1-to 2 Kg of shirasu are placed in a wood box, 100 cm long, 4.5 cm wide and 12 cm deep, and about 200 Kg can be loaded on one small truck. The average time needed for driving may be about 10 hours, and the mortality during the • transportation is not over l(r:. -68 -

When shirasu fishing is done in a small scale, • the transportation is done also by means of a truck but instead of the wood box as described above, a bamboo busket is used. In recent years, the transportation is done in /33 a span of much longer distances. Especially when shirasu- unagi is imported, it often travels 35 hours by plane. This author was successful in transporting 1 Kg of shirasu from Christ Church, New Zealand to Kyushu, Japan (32 hrs.) and from the airport to the author's laboratory (50 min.) by truck. The transportation was done on the 15th - 17th of December, 1969 and the survival of the shirasu during the transportation was 100%. The shirasu, for this transportation, • vi.ere prepared as follows, First, the hauled shirasu was stored in running water with 1400 of temperature for at least 2 days, and then 1 Kg of shirasu was divided into 3 polystyrene bags, and about 2 volumes of water, that is, twice as much as the volume of the fish, and oxygen was bubbled into the water. The bags were placed in a white styrol box (52 x 33 x 37 cm), and the temperature inside the box was kept at 5 to 8 °C. The most important precautions required in this processing are first to transfer the fish from a storage pound busket into low temperature water, 4 - 7°C, prepared by adding ice cubes, and only after the foam excreted by the fish disappears and the fish calm down (within 1 min. ) , to transfer it to • the polystyrene ba for transportation.

rz=remrr, -69-

2) Natural Fry (1) Present ,3tatus of Availability*of Natural Fry In Shizuoka, Aichi and Mie-prefectures where the eel culturing business is being developed by local aggregated organizations, the traders are importing natural eel for the culturing from Ibaraki and Chiba-prefectures, which are in the Tone water basin. The imported natural small eel are used as a stock for the culturing, in addition to shirasu- unagi. The demand of natural eel varies deoending on the locality. In Hamanako area, about 10 to 20% of the required stock for the culturing is the natural eel, and in Aichi- prefecture about 20% of the stock needed is the natural eel. • In ,souLhern,Mie-prefecturo, the stook for the culturing is almost exclusively the natural eel but in northern Mie- prefecture, the stock is mainly yochu prepared from shirasu- unagi. The inter-prefectural transfer of the stock eel has been done since 1919, but if the eel culturing business is to be started out in new areas, then the traders involved should try to collect the required stock at the same local area rather than importing from other areas, because by securing the stock locally, the fish are usually less damaged without being injured during the transportation, and the cost . is also lower. The status of natural eél haul in Ibaraki and Chiba-prefectures is as follows. The fishing ground is the lower Tone, the river Hitachi, and: swamps and ponds in Kasumigaura and Kitaura, The fishing season is between the middle of March and the end of October, and the peak period is between March and May. The eel caught is usually 15 to 25 cm long, weighing 5 to 20 g, The eel is usually supplied to the trader in the culturing business through the hands of a broker and wholesale dealer, but at times, the eel fisherman directly .deals with the buyer, The price is annually determined by the Price Control Board which consists of 10 elected business representa- tives in Ibaraki and Chiba-prefectui'es. About 60% of the haul is shipped to Shizuoka, Aichi and Mie 7nrefectures as the stock eel for the eel culturing, about 30% is shipped to Niigata, Gumma, Hiroshima, Yamagata and Shiga-prefectures to bè released into rivers, lakes, and ponds, and the rest, about 10%, is sold to buyers through the • Tokyo central market, It is truly regrettable that there is no statis- /34 tical data available to analyze annual change of the haul of the eel. The haul of stock eel in the Tone water basin in 1929 is shown in Table 4, The haul handled in 1958 in the same area is shovsn in Table 5. (Tables 4, 5 and 6) lamely, the total quantity of the stock eel handled is about 211 tons but if the duplicated count called "local /35

, . - • ' . •7'77 „. -71 .1•IM

s4e" which is actually transferred from one local wholesale dealer to another is subtracted, the net is 179 tons, which is nearly the same as recorded in 1)29. More recent data is presented in tables 6 and 7.

(Table 7)

(2) Fishing Methods Eels are caught with several different kinds of fishing gear and methods. They are a pound, bamboo tube, bamboo grass, long-bag-net, hand-haul-net, waiting net,

stretch net, eel weir, eel shack, eel stamping*'and others. Pound: An eel pound is made in a funnel shape by tying a large number of pieces of thin split bamboo with a thin rope at several parts. In order not to let eels that entered once • .,Into the IDOunfl elsope, the tail part of th Ind.,*s made with very fine split bamboo. As bait, an earthworm, short-necked , silkworm pupae, or mud-snail are used. Size of the pound varies from a large one with 1

to 1.5 m of length and 20 to 50 cm of diameter to a small one

with 70 to 80 cm of length and 10 to 12 cm of diameter. It may be used separately or several of them can be tied together with a rope. When it is placed in deep water, usually a marker is attached. The pound is placed at different sites in the river depending on the season. Since eels ascend river from the spring to late in the summer, and descend river

• * Y2ra11,31ato1' ;;bte: All these were literally translated,

■••••••,‘,7,7^'. closer to the river mouth after the middle of the fall, it is placed facing the downstream before the middle of the summer. One fisherman can handle 100 to 500 pounds. Dyke pound: This method is a combination of dyke and pound fishing. The dyke is built so that eels are.led into the pound, and it is usually used in rivers. The dyke may be built with small stones in an angle between 45 and 60 degrees from the river bank on the upper stream, and with a height of 40 cm. The dyke forces the water and eels into the pound. /36 The pound used is about 2 m long and 50 to 70 cm in diameter, and is made of the medake bamboo (Bambusa simoni) * with a diameter of 1.5 cm. The pound is placed at a rapid where the water is about 40 cm deep, and fixed with a stake on its bide, but sometimes on its front or rear end. The fishing season is between May and October, and the haul is large when there is a flood or during the night. Eel'Tube: This gear is used for fishing based on the eel's - nature of avoiding the light and hiding in a hole. In compari- son to the pound, the haul is usually poor, and it is time- consuming. This'method is, therefore, used only in capturing the last remaining eels in an eel pound after taking out eels for shipping or when a small quantity of eels are to be taken out during the cultivation period. A long-jointed bamboo (Phy_llostachzs bambusoides)** with 7 to 15 cm diameter is cut with two joints. One of the

Tn.insintnr's Addcd oy the tran;:slator. Perhaps this species.

** Translator's Note: Perhaps this species.

7,1°, - 73 - joints is broen open, leaving the other unbroken. If the bamboo tube is to be used in shallow water, both joints may be'removed. The length of the tube is between 70 and 90 cm. 2, thick tube may be used individually, and if a thin one, two tubes may be used by tying together. A hole is drilled close to the opening, a thin rope is attached through the hole, tied to a stake, and the tube is placed in the water. When the tube is to be taken out, it is slowly lifted from the water to the surface and placed in a net and the catch is dumped out. The open tube to be used in shallow water must be lifted after holding the both ends with the hand. A large number of the tubes may be used at à time by tying to a rope. Since the tubes are left in the water, it is necessary to

watch them clnsely and vP -ny of+Pn. Bamboo Grass or Brush Wood: These are used to catch eels based on their nature of hiding in dark, and the method is one of the most common used throughout the country.

About 1 m long branches of bamboo grass, chestnut,

passania, oak and other trees with leaves are tied together, and a number of the bundles are attached to a strong rope at 1.5 to 2 m intervals. One end of the rope is fixed to a rock or anchor. After leaving overnight in the water, the bundles are one by one lifted slowly to the. surface, and received in a triangular net. The bundle is shaken well above the water to catch eels and other small fish. This method is particularly useful in winter season, late in the fall to early in the spring. - 74 -

:el Stamping: • The season is around the hottest days of the summer. A four-armed scoop net is. set ab downstream of a river, swamp, lagoon, waterway or ditch in which the water is shallow and various deposits and precipitates are accumulated or grasses and weeds-are abundant. When the surroundings of the net are stamped hard moving towards the net, eels escape towards and into the net. Eel Shack: The fishing ground is downstream on a river where the water is calm and 40 to 60 cm deep. Round stones, about 600 to 1,000 g each, are piled up in a circle of 2 to 3 m diameter. The top end of the stone circle may be 20 to,30 cm above the water. Eels enter into this stone shack. To haul the catch, first the shack is covered with a net, and the stones are removed one by one. Eel Weir: This is one of the best methods of catching the descending eel in the fall. Two small boats about 2 m of shoulder width are moored about 8 m apart facing towards the stream, and secured with "dogi" beams. Two "tegi" poles are tied to the "dogi" 4 to 5 m apart. Between the "tegi" poles, a weir net is stretched. In a small river, a large part of 1:le stream may be blocked with stones and rocks or with bamboo fence instead of using boats leaving an open stream, where a weir net is stretched. The net is used only at night when it very dark. The haul of this method is excellent durin the rain, storm or flood. Lon;-raF-Let: This net is used mainly in the water basin of 41 the ri.ver ToneF:awa. The rishinF season is after both sprinr; and autumn equinoxes, and the net is used in moonless - 75 -

4c) -t only eels bit also shrimps, , maruta* and other

miscellaneous small fish can be cat4it. The fishing grounds

suitable for this net is where it is about 4 m deep with sandy bottom and the flow is rather mild.

The net consists of three parts, bag-net, wing- net and trap. It is a kind of stationary net, and quite large.

The length of the wing net is about 40 to 50 cm on one side,

and the lenP[bh of the bag net is 30 to 35 cm. The h et is

attached to 4 cedar stakes, with 7 m of length and 10 cm of

diameter. Two of these four stakes are driven into . the

river bottom 20 cm apart on each side of the river, and the net is stretched across the stream, being tied to the stakes with a metal wire. The end of the trap is attached to a pine

,stake..driven into the bottom to stretch out the whole net. The net is set in moonless nights between April and June, or in the autumn and a boat is usually moored beside the bag net.

During the night, the trap is lifted frequently, about 20

ties or more per night, and the eels are transferred to a

busket by releasing the sleeve ring attached at the tail part of the trap. The net is pulled up in the morning, and dried during the day. When the conditions are good, about

400 Kg of eels can be hauled in one night. Waiting Net: This is also a stationary net slightly smaller

than the long-bag-net, and the length of the wins net is 30 cm,

and the bag net is about 30 cm long. The net is used in moon-

less nihts of larch to June and October to'ovember, when

* Translator's rote: Transliterated. -76-

the tide is ebbing. It can haul about 200 Kg per night. (Fig. 11) Stretching Net: It consists of four parts, bag net, wing net, heciFe net, and trap. It is used in a lake, fixed to stakes, /38 to catch circulating fish, including eels. The length of the bag net is 5 to 6 m, wing net 20 m, hedge net 50 m and the size may be altered depending on the physical aspects of the surroundings. The trap is lifted in the morning and in the evening. Many kinds of fish are caught including a pond smelt, shrimp, tanago* and others. Eels are caught in a period between April and October. Hand-Haul-Net: This is a small draé net, about 6 m long in the wing net part and 6 m long in the bag net part. It is • cast overboard and hauled back into the boat, In both Ibaraki and Chiba-prefectures, the net is operated near the river mouth of the river Tone. The boat is motorized, and moves around in the fishing ground. The fishing season is - May to October. Sailing Net: It consists of two parts, one bag net and two wing nets. Both bag net and wing net are 10 m long. It is draied by a 1 to 3 ton sail boat with an 8.5 m high and 18 to 20 tan**wide sail. The layer of dragging is the middle and bottom of a lake, and commonly used in Kitaura area. As the u el s caud:It with this net have a large mortality rate during the transportation, the method is not favored very much.

* Translator's Note: Transliterated Probably Acheilovnathus • moriokae. ** Translator's Note: 'iidth of rolled cloth. About 35 cm.

'77Cre.,›"ZetV,K1,1,4±^,-3.,re • 6, 12J.;D 1) The digestive organ of the eel consists of a digestive tract or an alementary canal and peptic glands. The alementary canal is a long tract from the mouth to the anus, .and its stomach portion is expanded and bent forwards and then towards the anus. The peptic glands are the and pancreas. Mouth: The mouth cavity is covered with a thick mucous mem- brane with a large number of plicae. The mucous membrane consists of three layers, the epithelium, the proper membrane and the mucous lower membrane. The mucous membrane is covered with mucilage cells, and thé taste buds exist on the membrane. The teeth are small and shaped like a dog-tooth but quite uneven. They develoD mainly on both jaw bones. The tooth is not situated deep in its socket. It consists of a dentine and enamel but no cement. While the eel is at the leptocepfalus stage, it has several dog teeth of two different sizes on the upper jaw bone only, but they drop out during the metamorphosis to be displaced with the permanent teeth. The tongue is only a small projection but taste buds are very well developed and distributed densely and widely. The upper ends of the taste buds reach the external edge of the epithelium of the tongue and filled up with taste c,J.11s. At the lower end, these taste cells are connected with the terminal ends of the 9th tongue-throat nerve. Pharynx: It is surrounded by the gill arch bones at the rear • e:-.u7Ë of the =uth 12here are a pair of pharynx bones - 78 -

above and below it. Five pairs of gill slits are situated on each side. The teeth grown on the pharynx bones are extremely small. sophagus: It is a pale pink canal from the pharynx to the stomach, and has many plicae running lengthwise. At around /39 one third of the total length from the pharynx, there is an opening of the air passage, making a small projection. The esophagus consists of the mucous membrane, muscle membrane and fibre membrane. (Fig. 12) Stomach: It is divided into two sacks in a Y shape. The part where it joins with the esophagus is the joint of the two sacks. The upper and smaller sack is connected with the small intestine and the1ower .and _longer „s,ack .bas ,no.outZet connection. The joint with the esophagus is the cardiac orifice and that of the upper sack to the small intestine is the pylorus. On the surface of the stomach mucous membrane, there are a number of irregular plicae, and particularly in the lower sack, the plicae run both transversely and length- wise. In the upper sack, there are very fine wavy plicae • runninglenthwise but closer to the pylorus, the pattern of plicae.becomes simpler. In the cardiac orifice, the esophageal epithelium can be seen. There are small foveae on the surface of the storiiach mucous membrane, and at the bottom of each • fovea, the stoach clan onens. Closer to the pyloric rezion, - 79 -

the density of the stomach gland distribution becomes smaller • and the glands finally disappear. The stomach wall is made un with two layers Of muscles; the inner layer is circular muscles and the outer layer is longitudinal muscles. At the pylorus, the part of the muscles is quite thick, and the mucous membrane is elevated towards the pylorus in a few rings. Intestines: No particular distinction can be made for the intestine of the eel. Although the duodenum, small intestine, jejunum, and ileum cannot be seen clearly, at the part of the intestines, a little distance away from the joint of the stomach and intestine, the biliary duct opens and therefore, this part may be called the duodenum. It is a quite thick canal made of thick wall with several tens of plicae which run lengthwise. The rest of the intestine is short and its • surface is flat. There is one clearly identifiable valve between the intestine and the small intestine. Its mucosa is flat without villi but there are a larger number of cotyloid cells in the intestine than in the small intestine. The anus is always closed tight and opens to the combined cloaca together with the urinary tract. Pancreas: It exists in the space between the stomach and the intestine, and it is a yellowish white, meandering long belt. Its length is about - two thirds of that of the stomach. The pancre2s consists of the main duct gland and the Islands or Landerhans. There are terminal cells,- enzyme grameles, granules, and others. The main duct opens close to the pylorus. The /40 duct is one sinle canal on the outer surface of the intestine

"7'7777-7 M7r7 rwr-mmei`l - 80 -

wall, but within the wall tissue, it is split into three • small canals, and when it projects out into the intestine inner surface, it is split into a large number of very fine tubes. These outlet tubes exist as a mucosa-like, aggregated project. ;3oth pancreatic juice and bile are excreted separately into the intestine and only in the intestine, both are mixed and aid the digestion. The Islands of Langerhans are covered with very thin connective tissues in the pancreas tissues. Liver: It is large and rectangular and exists in the anterior part of the abdomen behind the diaphragm, and surrounds a part each of the esophagus, stomach and small intestine. It is reddish brown, and the left leaf'is larger than the other, and reaches the top of the stomach. The liver consists of • liver leaflets, and the terminal end is blunt. The gallbladder is deep green and egg-shaped. It is attached to the internal surface of the liver. • • (2) Digestive Enzyme Mouth and Esophagus: Saliva,which is common to all the higher animais and contains amylase, cannot be detected in the eel . a unit cell gland, which excretes mucous throughout There is t:_e mouth and the esonhanals. There are also lengthwise plicae along the gland. These help to swallow the food taken in throuc:n the mouth. Occasionally the esophagus is found to show an acidic reaction, but this is estimated to be due to the backflow of the stomach fluid, because there is no gland to secrete Densine in the esophagus,

-,tpmacl: In the stomach, an acidic diïsestive fluid is excreted, and it contains pepsin (protease). This enzyme hydrolyzes

r,,e5=m77.77.,N=M=7 7',er.›. - 81 -

proteins into proteoses and peptones, and the amount of excre- S tion of this enzyme varies depending on the position in the stomach. It is excreted more where there is food remaining longer. The optimal conditions for the activity of stomach pepsin are pH 3.2 - 3.3 and the temperature 40 to 50 00. When the rates of digestion of fresh lean meat of sardine and boiled lean meat of the sanie are compared, the fresh meat is known to be digested faster, and the rate becomes smaller as the heating temperature is raised higher. The decrease of the rate of digestion is esDecially remarkable at around 70°C, and therefore, if meat-is to be heated, it is better to do it at lower temperatures than 70 00. The rate of digestion is also better when sardine meat is fresh than when it is dried. Liver and Pancreas: The pancreas excretes insulin, which is eSsential for the metabolism of carbohydrates, trypsin (protease). 1 amylase, and lipase, and the liver excretes trypsine, amylase, and lipase. The optimal conditions for pancreatic amylase are n!: 6.5 and temperature 36 to 37°C to digest 2.85 soluble starch for 20 hours. These conditions are about the same as those of amylopsine of the higher animals. The optimal conditions of trypsines from liver and from pancreas are between pH 7 and 8 and temperature • around 1400C to digest 0,3Ç casein for 2 days.

r":.m:7-ege.p7menv:msTr",e4'.C.,,:e:7_ - 82 -

Besides these, invertase and maltase have been /41 detected. Intestines: The enzymes found in the intestines are quite numerous, because in addition to the enzymes excreted from the intestinal mucosa, the enzymes from the liver, pancreas, stomach and others as well as those of the food taken in, are mixed in the intestines. Furthermore, a flora of bacteria in the intestines also produce various enzymes. The enzyme excreted by the intestines are amylase, sucrase, maltase, lipase, invertase and as a protease, trypsin.

The optimal conditions of protease are pH 7.0 and

temperature 49°C to digest 0.255 casein for 2 to 3 hours. (Fig. 13) • -,e) -Organ -of -Smell-al-1d 2ense of .laàte The organ of smell of the eel is a highly developed one. Its size is almost as large as or larger than the whole brain. In a large eel culture pond, the eels gather to its feeding post when the feeding time approaches. Some of the eels even get up on the wooden floor of the feeding post and perhaps this is caused by their unbelievably strong sense of smell. The organ is a pair on both sides of the forehead and situated in a socket. It is covered with the nose bone.

There are two orifices, the front one is a tubular projected /42 openin situated at the side of the forehead and the rear one is an eval aperture in front of the eye just a little away, • from the eye. The smelling orépn.is connected to the outside - 8 3 -

throtwh these two holes and it is not connected with the buccal cavity. It is egg-shaped and has a centre axis. On both sides of the centre axis, there are a number of plicae covered with mucosa. In the mucosa, connective tissues, blood vessels, and nerves are distributed in high densities. (Fig. 14) * There is a close relationship between the degree of development of the plica in the organ of smelling and the size of the eyes of fish. The fish with large eyes have simpler structure of the plica. As the eel has small eyes, the plica is highly developed, the number of the plicae is also large, and the depth of plica is deep. The fact that the eel has a very good sense of smell has been experimentally proven, and also observed quite often. If a piece of meat wrapped in cloth is placed in a water tank, then eels in the tank are highly excited within a. second or two and start to feed on the wrapped meat. This proves that, for the eel, the sense of smell is the more decisive factor in starting feeding than the sense of sight. A minute amount of juice that comes out of the wrapped meat cont.3ins some chemical substances and these stimulate the cells in the organ of smell via the medium of water, and the stimula- tion is sent to the brain, which in turn drives the fish tow,i2ds the direction in which the concentration of the chemical substances is higher, and finally to the meat. In - other words, the smell is the first signal to drive the fish 11› towrds the direction and position of the meat, and -nerhaps only after the fish reach close enough to see, it identifies - 84 - • the meat, and when the meat is taken into the mouth, the taste is felt by the fish. The fish in general can differentiate four different kinds of tastes, sweet, salty, bitter and sour. Not only that, it has a very sharp sense of taste. For example, very sensitive fish can taste a sugar solution about 512 times more sensitively than the human being, and a salt solution, about 184 times. It is, therefore, important to be very cautious in preparation of the artificial feed. 3) Natural Feed The eel feeds on fish, shell fish, insects, Crustacea, Annelida and others. The size and shape of these food animals of the eel vary considerably, and therefore, the eel is .said to be quit e.omnivarous. The type of food the ._eel takes also varies depending on the environment in which the eel lives, on the size of the eel, and on the season. The type of food the eel takes is as follows. Annelia Echiuroidea Urechis unicinctus (yumushi) -hiruidinea Iliruido nip7)onica (chisui-hiru) Erpobdella sp. (ishi-biru) Chaetopoda Allolobophora foetida (shim-mimizu) Tubifex heteroche tus (ita-mimizu) Nereis janonica (gokai) Tylorrhynchus hetérochetus (itome)

Gastroboda Cipanopaludina malleatus (tanishi) • Semisulcospira bensohi (kawanina) Lamellibranchia Arthropoda Crustacea - 8 5 -

Alona spp. (shikaku mizinko) Lepas anatifera (eboshi kai) Neomysis sp. (Isaza) Paratya improvinsa (nuka ebi) Leander paucidens (suzi ebi) Sesarma haematocheir (akate gani) Idotea sp. (heramushi) Insecta Chironomus sp., Stratismyia sp. (mizu-abu) Cybister sp. (gengoro) Azuma elegans (oyama tonbo) • Anax parthenope (ginyanma) Agrionidae (itotonbo) Ephemera sp. (monkagero) Loxblemmus sp. (mizukado-korogi) Gryllotalpa afrieana (kera) and others and their larvae Pisces Pseudoperilampus typus(zenitanago) Pseudorasbora parva (moggo) Sarcocheilichthys variegatus (higari) Carassius auratus (funa) Rhinogobius brunneus (yoshinobori) The eel mainly lives on fish, insect larvae, shell fish, and shrimps and other Crustacea in fresh water such as a lake, pond or river, and on Annelida and crabs and other Crustacea in sea water, and on Cirrinedia in an inland bay. (Fig. 15) When the food is analyzed by the seasons, the results are as shown in the attached figure. The natural food varies because the availability of certain food species, especially Crustacea, Annelida and insect larvae, changes considerably from one season to another. Another factor that /44 deteluines the kinds of food the eel takes is the physical size of an eel. Shirasu-unagi, when it just enters a river from the ocean late in October to early in April, has only a a=unt of deitras in its diestive sjstem. Since - 86 -

shirasu-unaGi's colorless transparent gelatinous material in 1110 itE: body cavity disappears gradually by the time it becomes a krokko, the gelatinous material is considered to be the source of nutritional substances until it becomes large enough to take food from the outside. The food the eel starts to eat is mainly zooplankters, such as Neommis sp., Alona spp. and others, and as it grows bigger, it takes fish and Crustacea and other animal food. . A larger eel preys on a small eel quite often. When the body size becomes about 20 cm long or longer, the type of food it takes does not change any further but the amount that it takes increases. 4) Quantity and Variety of Feed • In order to culture the eel, fresh or frozen fish 5 is used as the major feed (about 99% of the total feed required). The species of the feed fish are a lockington, sardine, mackerel, horse-mackerel l spike, and others. Also used as a feed include a head of , silkworm pupae, fish powder and internal organs of various kinds of fish after preparing the process food. The table shown below is a part of the statistical data published by the DeDartment of Agriculture, as the .quantity of different kinds of feed used to raise cultured eel. The ::;:''ce of this table is Production Data of Fish Culturing Busines (1967), • (Table 8) Before the wnr, when the sardine haul was very

,■■-■ • - 87 - good and therefore its price was low, the sardine was the main feed for the eel culturing business. After the war, however, the haul decreased and the price of sardine became quite high. As a result, much cheaper kinds of fish, such as a mackerel and lockington became a popular feed. Besides these, a horse-mackerel, saurel and others are also used when they are cheap in certain seasons of the year. The feed also varies from one area to another, because miscellaneous kinds of fish are available in one area abundantly and they are available at low prices. These miscellaneous fishes are also often found in a haul of a drag-net fishing in many parts of this country. They may be used fresh or after freeze- storage. Where there are large industries of , the vastes-often processing the fish are also utilized for the eel culture business. For example, heads of bonito and /45 tuna are used in Yaizu area, and wastes after preparing fish- paste and fish-cake are used near Odawara. There may be many other kinds of useful yet unused sources of materials for the eel culturing business. As described previously, silk- worm pupae had been used as the only kind of feed for the cultured eel until the eel culturing business became quite popular.. However, because the silk yarn business fell into decay since then, the silkworm pupae are difficult to obtain these days , . and also the eel fed on silkworm pupae only develoo certain characteristic odor, and for these reasons, the- silkworrn pupae are no lon ger used in recent years. When they are used, it is only iuring tne i)oriod of waitini:; for a - 88 -

fresh supply of other feed, and therefore, they are considered to be only a supplementary feed. It is always ideal to use a fresh feed. If the feed is not fresh, or particularly if it is oxidized by air, it should not be used. If an aged feed is used, the eel fed with that may become ill due to nutritional disorder, and the whole business may end in a failure. Artificial prepared feed has been the desired feed by the traders in this business fôr some years. After the war, the research work on this subject has been emphasized and a large quantity of good quality, artificial feed has been prepared for the market. HoweVer, the traders in this business tend to stick to the traditional fresh feed, for there certainly is a fault in the artificial feed that it does not exactly satisfy the eating habit of the eel. The fault is under reinvestigation and being improved, and there

is no doubt that the artificial feed for the eel will become the basic feed. Since not only the eel culturing business but also culturing other kinds of fish is . becoming popular, obtaining fresh natural fish for the use as the feed will perhaps become more difficult in respect to price and quantity available. It is, therefore, quite natural to expect that the synthetic or artificial feed will become the basic feed in

any type of fish culturing business. It is to be emphasized that the future improvements of the artificial fish feed

should be a.lon the line of improving the product to satisfy • the eatinL; habits and fondness- of the eel. When the fresh fish feed is given to the eel, if - 8) -

the fish is fed to the eel as it is, then the growth rate of 110 the . eel is better.' has been known not to be as good as the really fresh fish. Besides, there is a tendency that the eel fed only on the fresh fish has softer skin, yielding more slime, and has a shorter body length but more fat in the subcutaneous fat layer. 5) Method of Feeding The Japanese eel is different from most other kinds of eel in that it lives in the temperate zone while the others live in the tropical zone. The Japanese eel stops feeding when the water temperature is as low as 8 to 10°C and stays still in mud, or under rocks and stones in rivers as if it is in hybernation. It resumes feeding when the water temperature rises to 10 to 13°C and as the temperature rises higher, it takes more food but at 28°C or higher, its food uptake decreases again. Therefore, the optimal tempera- ture range of feeding is between 20 and 28 °C. Since the weight increase of the eel is related very closely to the amount of feed it takes, the area where the period of the optimal temperature for feeding and, 'herefore, the period of feeding which is longer per year is a better place to do the eel culturing business. Usually, the period between late November and the middle of March is the period in which the eel does not feed in Shizuoka, Aichi and ;:i.e-orefecture. Fresh or frozen fish may be given to the eel by

11› bas.sin a stick throuit their .,,yes and haninG the stick and

717=-:777"="1.7,.717n7eMu_kM=1 ",ewsiegeffleemeitege, - 90 -

fish into the pond. The fish may be boiled and the boiled fish placed in a basket may be lowered into the pond. There are three types of feeding fish. They are feeding fresh fish only throughout the year, and this bends to deteriorate the water; feeding boiled fish only as it keeps good water quality; and feeding fresh fish as a /46 "fish and stick" early in the spring and late in the fall, but boiled fish during the period when the eel feeds well. The last method is the one adopted by a larger number of traders in this business, and it is quite difficult to choose one best method. They all seem to have advantages and disadvantages, and perhaps the most scientific method of feeding is to vary the feed preparation depending on the season, quality of water in a pond, conditions o-f the eel in the pond, and of -course on the kin d of feed available at the time. (Fig. 16) When large fresh or frozen fish are prepared for feeding by passing a stick through the eyes, its abdomen is teared from the anus towards the head, by'sticking a finger to the anus. nen a lockington, mackerel or mackerel pike is used, it is put in boiling water for 'a second to soften its bard sWin, because the skin of these fishes is too hard for the eel to break, but not to boil the meat. VI'. T. Inaba classified feeders into - the following

2 t,-:; 7,s, t1-.db the uuy a man feeds the eel truly ' r,:-:f1t2cts hie per,bonalitj. • Une-Gretch Type: This type mainly includes the feeders who - 91 - have artisan spirit. They may judge.the quantity of feed to be given based on their experience of many years judging the weather conditions of the pond, and conditions of the eel, and feed the eel at once. They may finish the job in half an hour or an hour. This type of feeding is really good, because it is based on the nature and characteristics of the eel. The eel lives in a typical society in which the weak become the victim of the strong, and the larger and stronger .eel always eat the best part, delicious and nutritional, of the feed first, and the weaker and smaller feed on what is left after the stronger have finished eating. This method • of the feeding aims at the feeding Of the fast growing group. . When the area of the pond to be looked after is large, perhaps this method is particularly suitable.. Coordination Type: This is the type of feeding based on the very cautious analysis of ater quality, required amount of feed, conditions of the eel and so forth. The men of this type can feed the eel very well throughout the year and also good in conditioning the pond. Therefore, the feed efficiency and productivity of the pond are excellent. The men of this type are also thoroughly capable of training the eel to the feed and perhaps they do not need to freshen up the pond water too often. 1,ingering '2ype(Chrysunthemum Type): This type of feeder is too eaer in feedinf:; the eel and even when the eel is completely s:Itisfied u .ter fininin eatin, he keps eelo have haà enouh, a lare Ero .op of eels, about 15 to 20 -isg, /47 - 92 -

swim around the feeding post in a large circle eating what • is left, only a little by littIe and slowly. The way they swim looks like a chrysunthemum flower, and so this type of feeding is called the chrysunthemum type. In short, this type of feeder is very reluctant in leaving the feeding post. The feed efficiency is very poor in this type, wasting a considerable amount of the feed and the management result is poor. Save-Face Type: This type of feeder feeds on the prescribed and usual amount of feed, probably knowing that the water quality is not good, that the eel is not going to eat well, and that a lot of the feed will be Wasted. This type offeeder can be found often amoung the feeders working at some organized • eel culture A.re,q. 6) Feed Quantity Based on the results of testings and research, and the experience that the traders cumulated in many years, they usually set up a standard of the feed quantity for a specific eel culture pond. The standard is roughly about 6 to 7 Kg of feed consisting mainly of fresh or frozen feed to increase about J. Kg of eel meat. . The daily feed quantity is about 10% of the estimated weii;ht quantity of the total eel in a pond, but it varies dependinL; on the size. of the eel. During the feeding

CL shirasu-unai, it is 10 to 15 , and for yochu, 7 to 105 is ade ..,luat;, . • - 93 -

During the period of feeding juvenile eels until they become about 150 g of body weight, the efficiency of feed to be converted to the eel body meat is better while they are smaller. The feed efficiency decreases as the eel grows, and after it reaches 150 g of body weight, the feed is consumed more to keep the eel body in good health. This feed consumed for maintaining the eel's body may be called maintenance feed. Consequently, in order to keep the best feed efficiency, the feeding should be best stopped when the eel becomes a medium size. The business of supplying the stock eel to the eel culturing business for further feeding is made up based on this principle. At the same time, for the eel culturing business to bring up and market Ibku is a waste of feed. The daily quantity of feed also varies depending on the weather, water quality, and water temperature. When the water temperature and air temperature rise high, the feed quantity becomes larger in proportion to the rise; when the sky is clear the feed quantity is larger than'when the sky is cloudy or raininR; when the wind blows the feed quantity is larger. Regarding the relationship between the water. the feed quantity, the feed quantity decreases tem-eerature and as the temperature rises above 30 °C. The quE,ntity of eel to be accommodated in a pond cEll be estiïnated by the daily feed quantity and the time 11› required to consume a fixed quantity of feed. The shorter the - 94 -

feed consumption time is, the better the appetite of the eel is. The water quality must be always good, and since this factor is different from the weather conditions, control- able, an attendant of the pond should try his best in exercising his knowledge and skill. It is also advisable to have a water stirrer of some kind fixed near the feeding post, and operate it each time before starting feeding so that the oxygen concentration in the water, particularly near the feeding post, is maintained at a higher level. /48 7) Feed Coefficient This is also called feed efficiency coefficient. It is the value obtained by dividing the total weight of the •eed .supplie.d during the period with .the total bp ,',,y wPight increase of the eel in one pond during a certain period of feed, that is, a sum of the weight of eels taken out of the pond for shipping and the weight of the remaining eels minus the total weight of the eel released into the pond at the beginning of the feeding. Therefore, the.smaller this value is, the better the efficiency of the feed. It is usually excellent in shirasu-unagi and poor in yota. • The relationship between the feed efficiency coefficient and the number of days of feeding is shown in 2igure 17. (Fig. 17) Jescrbed urevLoesly, about 7 7.:z of fresh • is 2t-,luired to ircrcas 1 of the body i,e1.1.;ht of eel. - 95 -

However, examining these weights, it is noticed that, since • the eel eats only the meat of sardine leaving its bones, taking the average value 25.5% of the weight ratio of sardine bones to its total weizht varying between 20 and 33%,by seasons and locality, the actual required sardine meat to increase 1 Kg of the eel meat is 5.22 Kg. In addition, since a part of the fat and oil from the sardine fed to the eel floats up to the water surface during the eel's feeding, and it remains on the water surface after combining with other organic substances in the pond, substracting this loss estimated at about 7.3%, or 0.383 Kg, the net requirement of the sardine meat to increase 1 Kg of the eel meat is 4.832 Kg. The unused portion of the sardine given to the eel can be utilized for other purposes, the residual bone being used as chicken feed, and the oil combined with miscellaneous organic matter being used for extracting an oil mixture. 3) Mixed Feed As one of the means of reactivating coastal fisheries industries, shallow-sea cultures of high class fish, crabs, shrimps and other are being promoted under the name of culturing fisheries, and they are becoming popular every year. As the techniques of producing the stocks of these sea animals to cultivated and general culture techniques of Le stocks to finished products become highly advanced, the future of the culturing fisheries is Very promising. • The problem is that, in all these culturing

, 'e7MMr777 - 96 -

fisheries, the feed used is fresh or frozen sea animals almost the same as that used for the eel culture, and the feed efficiency coefficients in these new culturing industries are about the same as that in the eel culture or perhaps only a little better. The feed cost is about 49 of the production cost or about 70 to 80% of the total maintenance cost. Therefore, there is no doubt that the price of fresh or frozen feed fish is rising higher. Thus, in order to modernize the eel culturing business and rationalize the management, the /49 demand for artificial mixed feed is becoming higher. It was-in the autumn of 1957 that the mixed feed was first marketed for the èel cultilring business, but later, it was found that although the mixed feed is perfect in terms of nutritional sciences, more consideration has to be paid to make it satisfactory to the eel's senses of smell and taste, and to match with the eel'S eating habit. In order to make the taste of the cultured eel very much like the taste of natural eel, the iodine value of the fat of the eel must be taken into consideration. Theoretically, by feeding the cultured eel with feed containing oleic acid at a hiL;her concentration but hii;hly unsaturated acids at lower concentrations, this can be achieved. The oil from rice-bran contains methyl oleate at a hieh concentration and rice-bran is very cheap. Therefore, use of this material as an additive to the mixture feed is very desirable. It bus been noticed that when a certain kind of fish is always used as the only food for a iroup of eels, then the eels loose

erlZ,MIVC,7:-.,n,ert,mceferec.,7rree..5-Ye - 97 -

the original taste of the natural eel, tasting only like the • feed fish itself. Therefore, the traders often apply the so- called "ikeshime" method of removal of the unfavorable fatty acid from the eels to be marketed in a short while. However, application of this method results in decrease of the body weight. If, however, favorable fatty acids could be added to the mixture feed, then the "ikeshime" needs to be applied only for a short period to empty the contents of the digestive .system.

Translator's 77ote: Literally "alive-squeezing". Probably reducing the feed to the minimal level or to zero enhance the lipid metabo- • lism in the eel's body. - 98 -

7. .LUVIRONIT1 1) Respiratory Organ and Tactile Organ The major respiratory organ of the eel are the which are situated in the buccal cavity but the respira- tion also takes place, although not significantly, on the skin, buccal cavity wall, intestine wall, fins, and the air bladder. The gill is morphologically homologous to the lung of land animals, and its function also resembles very closely to that of the lung. The four pairs of gill consist of a large number of gill lamella, on which capillary vessels are distributed in a high density. The capillary vessels are in contact with the external water thrOugh a very thin membrane of unicellular layer, and excretion of carbon dioxide gas and 5.11s2,7pfion of r)xyg.n take place thugh thi. membrane. The gill is capable of absorbing not only the oxygen dissolved in the water but also the gaseous oxygen physically included in the water. Therefore, if the air is highly saturated with water vapor, then the eels can survive in the air for a period of considerable length. The trans- portation of the eel is based on this principle. The fact that the Gill slits of the eel are quite small is truly useful in retainirc the moisture in the buccal cavity. Tihen the wnu.-r quality deteriorates, the eel can survive by "hana-ag It* taking . the oxyGen directly from the air near the water 2fuce. Therefore, it is also useful to bubble air throuc;h

s)_: or 10 1e Literally "nose-liftin". - 99 -

the bottom of the pond to aid the eel in the respiration. • There are a few characteristic actions that the eel performs relating to the respiration. One is stopping of the respiration in the,mater for a while. First an eel spews out the whole water in the mouth and thon closes its mouth shut tight, stopping the gas exchange completely for some period. This action of the eel takes place often when the /50 concentration of the dissolved oxygen is relatively high, the water temperature low and the water quite calm, but seldom when the dissolved oxygen concentration is very high, the water temperature and the water being disturbed. Generally, it occurs when the water temperature is lower than 17°C. The longest period of stopping the respiration through the mouth recorded is 8 min. 20 sec. when the water temperature was The longest accumulated period of stopping the aspiration per hour is 37 min. 32 sec. (in 8 times of stopping) within 1 hr. Frequency of occurrence of this phenomenon decreases as the water temperature rises higher, concentration of dissolved oxygen lowers, concentration of dissolved.carbon dioxide rises and the activity of the fish increases. The phenomenon has been interpreted as the natural regulatory action of the eel not to loose'much carbon dioxide from the blood into the water, and thus to control the respiration. The second peculiarity of the eel's respiration is iLs one sill respiration. This is a phenomenon known only to the e.s:1, One ,ide of the opercula is completely closed cparculum is :3o tih ly cloed that it is - 100 - sunken. While it respirates through the other side of the gills, the degree of the respiration is deeper than the normal respiration, and the amount of water filtered is also larger. The efficiency of the oxygen uptake is not at all lowered as the number of the respiration is increased to as many as 1.5 times that of the normal respiration. Therefore, this one side gill respiration is actually efficient enough to support the normal metabolism. It tends to occur at lower temperatures, and the highest temperature of the observed occurrence of this phenomenon is 19.2°C. The third one is the eel's skin respiration. When the gills are not used for the 'respiration, a considerably large quantity of oxygen is absorbed through the skin, and also when the skin is exposed to the air, carbon dioxide is also excreted from the skin. Therefore, if the temperature is lower than 15°C, the skin respiration is sufficient to support the life. At the water temperatures between 7 and 80C, about three fiths of the reauired amount of oxygen is supplied through the skin. This is significantly important while the eel is being transported, exposed to the air with only a small amount of water. (1) Relationship between Water Temperature and Respiration Within certain temperature range, the respiratory aotivi -ty of the eel increases as the water teperature rises, Generally speaking, tho oxygen consumption increases 2 to 3 tires when the water temperature rises every 10°C. Therefore, cri e(-1.11a1 volume of water containin ;7; en ernlal ,:mantity of oxytren

r - 101 - can support respiration of 2 to 3 times as much at 5 °C as at 15°C. (Fig. 18) The number of respirations of the eel is between 12 and 92 times per minute, being smaller at lower temperatures and larer at higher temperatures. Although it tends to increase as the water temperature rises as high as 32 to 36°C, /51 when it is higher than this range, the eel looses the respira- tory activity and dies. At 2000 of the water temperature, the number of respiration is normally 50 times per minute. When the eel respirates, it opens the mouth and expands the gill arch, spouting out . the water in the mouth in one motion through the gill slits. Sometimes it expands the (Thestspreading the pectoral fins. This action is called yawning, which is a kind of physiological reaction of the eel. It occurs more frequently When the temperature is high. If it Occurs at low temperature, the oxygen concentration in the • water is probably low. As a means of expressing the rate of respiration, raspiratury quotient is usually used. This is a ratio of the ehuGted carbon dioxide to the amount of oxygen consumed;

R.Q. = p0 2/0 2 . Using this value, which kind of chemical secies of the boay components has been mainly consumed can be estIted. ;:amely, a larer respiratory quotient value metabolic consumption of the body fat and proteins, :;1j a :,11er ,:2sc)irntory quotient value shows that carbohy- rcU_Dn of th 'i body components. - 102 -

The respiratory quotient is not a constant specific to any one species of fish. Instead, it varies dependinc on the water temperature, body size, activity of physical motion of fish, season, age of fish relative to its reproduction oeriod, and other environmental factors. (2) Oxygen Consumption The quantity of oxygen consumed by the eel under' cultivation is one of the major factors to determine the . capacity of the pond in which eels are being cultivated; that is to say, the quantity of eels to be accommodated in a pond is determined by the oxygen consumption of the eel. The knowledge of the oxygen consumption is useful in solving some problems which arise in the eel culturing business, such ,as "Jaana-age".and „transportation. (Fig. 19) Generally, the'amount of oxygen consumption increases as the water temperature rises, and there is a linear relationship between the two . at the temperature range between 10 and 35° . However, at lower or.higher temperatures th.in these limits, the oxygen consumption decreases quite

';;hen the oxygen content in the water is below 2 ml per 1L, the number of respiration increases, and the amount of oxy,:;en consumption decreases. Also the amount of oxy,en consumption is lar,i2,er when a number of eels are together w':-)en only one eel is in the water, - 103 -

The amount of oxygen consumption is larger in proportion to the body length and body weight. (Table 9)

• The most practical and impOrtant problems related to the amount of oxygen consumption is to know the minimal amount of the oxygen consumption that the eel can tolerate in oxygen-poor water, as in the case of "hana-age". The eel has been considered to have strong resist- ance, to the low oxygen conditions because of its ecological and physiological characteristics. When the dissolved oxygen is 2 cc/liter and water temperature is 16 to 17 °C, the number of respiration is 1.45 times* and the oxygen consumption decreases as much as 9%*,

_and2vihen_the_dissolve,d,oxygen content is 0 .79 cc/litre at the same temperature, the respiration number increases to 2.9 time's and the oxygen consumption decreases to 23%. Based on this data, the iminimal oxygen concentration has been considered to be 2 cc/litre. (Fig. 20) (3) Tactile Organ The main tube of the lateral line starts at the back of the head and ends at the tail, end there are about 4 holes. On the head, there is one side tube each at the • 11/53 upper jaw, lower jaw and on the operculum. The cross section of the tube is eu;-shaped but the centre portion is slightly

t Tzalut:)r's- ,_;t:andard values are not ts.;iven. - 104 -

indented, and on the surface portion,. it is pressed slightly towards inside. The portion leading outside of the skin is gourd-shaoed, and there is one small arch-shaped, springy

* and scale-like plate in it. Both ends of the plate are fixed and the centre portion is free. On the inside surface of the plate, the vagus is finely distributed and it transmits changes of the external water pressure and the wave-motion of water. .2) Water Required Not only in the eel culturing business but also in any other fish culturing business, the water must be abundantly available and harmless. As the eel is the warm- water fish, the water usually used in the past is the surface water like the water taken from „a ,-ivcr" and .lake or the irrigation water. But in the recent years, synthetic agricul- tural chemicals are used in large quantities in rice fields and consequently, the surface water cannot be used safely. To replace it, water from an artesian well, infiltration water, and other underground water are being used. In that famous ilamanako-area eel culture zone, the water is being taken from the ground almost 400 m deep. Thus, the amount of available underground water determines the manageable size of the eel culturing business, and therefore, it is now one of the most important factors in choosing the area to establish thi rusiness. This iToortant factor, availability of water, 13 alo jus t; as important in any ot:3,r ;=ufacturin industries • and thecefc)re, the keen competition for the water needs very - 105 -

careful consideration at the higher level of government and private industries. The eel culturing business has often developed near the coast, and particularly in the adjacent low yield aGricultural lands or in unused salt farms, and perhaps the sanie tendency would continue in the future also. When this type of land is used for fish culturing business, even when fresh water is used as the basic water of service l .there is always a variable amount of sea water coming in to mix with the fresh water. (Fig. 21) The underground water iS the water of rainfall, ice, and snow infiltrated deep into the ground by gravity and piled up on the underground rock terrain ; throuP7h which the water cannot infiltrate any farther. When the underground water reappears to the surface through natural routes, it is called spring water. There are two kinds of spring water, one is hot spring water and the other cold spring water, and there are three causes for the spring water to occur. First, it can occur when a nonpenetratable layer, on which the /54 infiltrated water is held, is exposed to the ground surface; secondl.y, when there is a nonpenetratable layer above a water rich layer or water layer, and the nonpenetratable layer has a crack; and thirdly, when, because of the ups and downs of 'uhe c,round surface, the level of the underground water crosses • with the 'round surfaces.

. . . •• • •-•- • 1, • ' "" - 106 -

An artesian well is an artificial spring water. If, underground water is between two nonpenetratable layers, then the underground water can be led to the ground surface or above by the natural force or by sucking, after breaking the upper nonpenetratable layer by drilling, and piercing a pipe through the drilled hole. Its principle is, therefore, the same as for the second cause of the occurrence of spring water described above. Since the underground water has almost constant water quality and temperature, it is suitable as water for the use in fish culturing, but it lacks the oxygen and has too much of the soluble organic materials, but these disadvan- tages can be corrected by exposing the water to air for a considerable period of time. (1) Water Quality 1. Chemical Characteristics pH: The water in an eel culture pond shows pH above 8 under normal conditions, and the water with pH lower than 7 ls abnormal water. Generally speaking, when there are both free carbonic acid and a bicarbonate salt coexisting in water, its i-)1 value is proportional to the concentration of carbonic acid and inversely proportional to the concentration of ,the bicarbonate.* The surface water is always exposed to the air, and due to ne anabolism of vei:etation in the water, the

:7,taent is incorrect, end should be reversed. - 107 - carbonic acid content is low and consequently, pH of the surface water is neutral or slightly basic. In the case of underground water, When carbonic acid concentration increases as a result of decomposition of organic substances, its . pH becOmes slihtly acidic. Bicarbonates make its aqueous solution neutral or slightly acidic*, and at the same time, it prevents the water from changing the pH quickly to acidic or alkaline, when a strong acid or alkali is added. When anabolism of the vegetation takes place, carbonic acid in the water is consumed and the pH of the water becomes alkaline. In most . of the eel ponds, MyxoEnycea l often called blue powder**, is quite heavily grown. As a. . result, during the day when its anabolism takes place quite actively, pH of the water in the pond becomes 9 or 9.6 at the highest, and at night when no anabolism takes place, the pH becomes again neutral. When the sky is cloudy or when it is raining, the rise of pH is not serious. If water pH is below 7, the water is abnormal. Since the pH of water heavily depends on the concentration of carbonic acid, if the salt concentration is high, the alkalinity of water is large, and corresondingly, the carbonic acid concentration is also high. Change of pH in a pond mainly varies in proportion to the concentration of carbonic acid. Soluble Orzanic Substance: The amount of total floating rlaterials in normal eel pond water after air-drying is 12.00 -

* s lote : To be ailine ** Translator's note: Litera11,7 translated. - 10 -

252.00 mg/1, and that of total organic substances (dissolved in the water)* is 70.08 - 306.97 mg/l. In abnormal water, the corresponding values are usually smaller. Namely, the amount of total floating substances is 3.50 - 145.00 mg/1 and that of organic substances is 40.29 - 869.00 mg/i. The larger values in the afore-cited are due to sudden withering of phytoplankton caused by a change of water quality. Water Soluble Gases: To the amounts of gases that dissolve in water, both the Dalton's Law, which states that particles of a gas repel only their own kind and have no effect on particles of other gases, and that in.a closed container, eaCh gas will exert the same Pressure that it would exert if it alone were to fill the container, and the total pressure will then

..be the sum of the partial pressures of the constituent gases /55 of the mixture, and the Henry's Law which states that the volume of a gas that will dissolve in water is independent of the pressure, but the weight of the gas that will dissolve ià directly proportional to the pressure, and furthermore, the weights of the various gases in solution differ from one another, and that a given volume of liquid at a specific teinperature dissolves a mass of a gas proportional to the gas' pressure, are related. This is to say, if the temperature of 'ater is identical, the gas dissolves more in the deep layer of the water than in the shallow layer, and more in water on the lower land than in water . on the hicher land.

* I'rrnislator's ::'".ote: Added by ne translator.

°7-e, - 109 -

When the pressure is identical, the gas dissolves more in cold water than in warm water. These are the most essential facts to be fully understood when the oxygen solubility in culture ponds is to be discussed. Dissolved Oxygen: The oxygen dissolved in the water of culture pond is essential for the respiration of eels in the pond, and it is also the source of chemical required for oxidations that take place in the pond. This oxygen is constantly supplied by the anabolism of the vegetation in the pond and from the air in contact with the water surface. These explain why the "hana-age" is not seen when the wind is strong and ruffles a pond, or during the daytime. The dissolved oxygen, however, is not only consumed by eels in a_pond but also by other animals in the water (fish, zoo- plankters and other miscellaneous animals living in the bottom soil) and by aerobic micro-organisms. Since phytoplankters are abundant in an eel culture pond, the oxygen concentration is quite high on the surface because of the plankters' anabolism, but when . the temperature rises during the day, organic substances decompose cuite rapidly consuming the dissolved oxygen in the lower water layer, and there occurs a considerable difference in the amount of oxygen between the surface layer and bottom layer. The amount of dissolved oxy;:en in a pond varies dperldin on quantities and kids of animals and plants in the !;ch:d ter , 1u2ntities of oxidied muteril in the pond, • weur eûr,ditic,ns articu .L?Çrl,y 1,y the water tElperabure, - 110-

wind velocity, and amount of insolation. When there is a higher degree of vegetation, the daily variation of the oxygen content caused by the daily difference of the insolation amount is more serious. • The "hana-agen phenomenon is caused by the lack of dissolved oxygen but the lack of oxygen in the water is not necessarily the cause of death during the "hana-agen, because even when there is a sufficient quantity of oxygen in the water, there could be a Sudden change of water which leads to the death of eels in the pond. Therefore, a line should be drawn to differentiate ordinary nhana-age" and "hana-agen caused by a change of water. The lowest limit of the oxygen content in water

1-4.- -tev,oui.ep ',Jae _Li.L.w _of eels in .a pond_is " b e

0.5 - 2.5 cc/1, Therefore, if the eels do "hana-age" in

water at thisoxygen level, there are perhaps some other causes for that, other than lack of oxygen. In fact, there are reported cases of survival of eels for 10 to 31 hours at

1.0 cc/1 or even at 0.06 cc/1, though nhana-age" was quite serious. These are perhaps explained based on the relation- ship between the skin respiration and water soluble carbon dioxide quantities under these conditions. The minimal and maximal soluble oxygen contents have been reported to be as shown in the following table,

(Table 10) The minimal quantity of'dissolved oxygen is larger • if the water temperature is higher. The change of the soluble - 111-

oxygen content during the daytime appears to be controlled mainly by the phytoplankton in the pond. Thus the time of /56 appearance of the highest oxygen concentration is between 2 and 5 P.M. when the accumulation of the oxygen by the anabolism of phytoplankton reaches the peak value, and the lowest oxygen concentration occurs before or after sunrise. The timings of these extreme values during a one day period vary depending on the wind velocity and the amount of insolation. In order to increase the oxygen concentration in a pond by artificial methods, the following methods have been utilized. Namely, bubbling, compressed air through the bottom of a pond, supplying fresh cold water into a pond, stirring the surface water with a mechanical stirrer to expose the _water to the,air,and_cycling the pond mater _by.a mechanical sprayer. These methods are based on the principle of either introducing air into the pond water to be enriched or to add. oxygen rich water into the existing pond water. Carbonic Acid: Carbon dioxide in the pond water originates from degradation of various organic substances such as residual feed, excrements of eels in the pond, and corps of plankters in the pond, from respiration of eels in the pond, and from metabolism* of vegetation in the pond water. Therefore, its concentration is usually larger during the night and smaller during the daytime, that is, the reverse of the oxygen concen-

* Tran.slator's Note: By apparent mistake, the author uses the word anabolism,

1

• reemnee5 ?nee - 112-

tration in the pond. During the daytime, when the vegetation carries on the anabolism, carbon dioxide concentration is nearly zero or negative values*, and if it is high, the water must be under abnormal conditions. The fish usually are quite sensitive to free carbon dioxide, and when its concentration increases, it no longer can respirate and starts doing "hana-age". Although its fatal concentration varies depending on fish species, it is expected that most of the fresh water fish die if the carbon dioxide concentration is higher than 290 mg/l. This carbon dioxide intoxication tends to occur more often as a result of decay of organic substances than the suddenly increased metabolism of the vegetation. When the carbon ,dioxide dntoxition tpka place, the first eMpl".nM. the eels' "hana-àge". According to the recent studies, when carbon dioxide concentration lowers too rapidly, the vegetation, particularly phytoplankton in the water can no longer survive, and this is one of the major causes of "changing water" in the eel pond. Hydrogen Sulfide: The major cause of formation of hydrogen sulfide in water is assumed to be the reduction of sulfuric acid bj the sulfuric acid-reducing organisms in the water, and the eel rearing pond appears to be equipped with ideal conditions to accommodate the organisms. Especially when oxygen content lowers in a pond filled with sulfate-rich water, hydrogen

• * Translator's Uote; Perhaps this means below average. - 113 -

sulfide is generated quite easily, and the eels in the pond may suffer quite seriously. Since the sulfate concentration is much higher in a pond containing salt water than in a fresh water pond, hydrogen sulfide can be generated much more easily in the former. Therefore, it is particularly important to equip such a pond with an efficient oxygen supplying device. For the generation of hydrogen sulfide, presence of iron is required. The iron in water can fix hydrogen sulfide generated as an insoluble complex, reducing the hydrogen sulfide concentration and keeping the reduction of the sulfates to hydrogen sulfide continued in the water. Therefore, an especially careful observation is required when a pond contains iron in the water or in the bottom mud. On the other hand, manganese can inhibit the reduction of sulfate to hydrogen sulfide, and therefore it is quite a usefill chemical in deactivating the action of the sulfate reducing organism. - Nitrate and nitrite also have the same inhibitory activity. /57 Magnesium has been known to be a required . chemical species for the activity of sulfate reducing organisms found in mountain streams. As described above, iron is an efficient remover of hydrogen sulfide. In fact, red soil containing iron in high concentrations has been used as a hydrogen sulfide remover by simply spraying it on the bottom of eel ponds. When the iron in the added soil reacts with hydrcwen sulfide, it is •

MeM2",g1r-"re,-, nyAn7,7,17 - 114

converted to iron sulfide and when this occurs, it appears as if the hydrogen sulfide is Dermanently fixed. However, later when the reducing aCtivity of the bottom soil increases, the layer immediately above the bottom.soil tends to have lower pH and smaller oxygen concentration and the hydrogen sulfide once fixed is liberated, and the iron itself is also eluted out into the solution as reducing iron. These inhibit the cleaning action of the bottom soil. Therefore, application of this method, that is, spraying the red soil, should be undertaken only as a temporary measure of suppressing the hydrogen sulfide concentration r . Based on these findings»described above, it is becoming a popular procedure to apply a chemical calle'd "genman" to ponds in which gas generation is pronounced or "hana-age" of eels takes place often due to lack of oxygen. The chemical is a mixture of powdered limonite calcinated at low temperature and a few other kinds of minerals. Its composition is as follows. Iron Oxide Lime Silicic Acid Manganese Others 34.61 6.05 38.54 4.27 16.53 The toxicity of hydrogen sulfide against the fish is reported using juvenile carp fish. At 1.3 ppm, it started to show the symptoms of the aerophobia against the gas, and the fatal concentration of sodium sulfide was between 0.55 and 8.00 ppm. The highest concentration of hydrogen sulfide recorded in ponds actually being used to rear eels was between 11› - 115 -

5,22 and 8.91 .mg/1. 11, Chlorine: Since most of the eel culturing ponds are situated near the sea, the water in the ponds tends to contain chloride, but the concentration varies considerably depending on the position, distance from the shore line, geological features and nature of the soil. Among the large eel culturing zones, the lowest concentration, 0.1 o/oo, was found in Kawaziri area of Shizuoka-prefecture and the highest concentration was recorded in Mie-prefecture, where 51% of the ponds in the prefecture had lower than 2 o/oo of the chloride concentration, 90% of the ponds lower than 5 o/oo, and 10% of . the ponds between 5 and 8 o/oo of high chlorine concentration. Althoueh free easeous chlorine is toxic to fish . if its concentration is below 1/150,000, it is harmless to the eel and carp fish, and therefore, it is Used to remove ikari- mushi and other harmful insects. Calcium: Calcium accelerates decomposition of organic sub- stances and it also exhibits an antagonistic action against some harmful components in the pond water. When it coexists with manganese, it accelerates growth of Microcistis. The calcium concentration in eel culture pond varies depending on the types of water used, but if lime is sprayed, it increases. On the other hand, when pH of the water is raised considerably as a result of decrease of carbonic acid concentration, it orecipitates'as calcium carbonate and

7rrellre:1:.7.7,!‘77, - 116 - as a result, the ionic concentration of calcium is lowered and the basicity of the water is also lowered. Nitrate, Nitrite and Ammonia: Although concentrations of these inorganic nitrogenous ions in the pond water are rather low, they are essential for the syntheses of proteins in the vegeta- tion in the water. There are both inorganiC and organic nitrogen compounds in the pond water. Among these, three inorganic nitrogen compounds, ammonia, nitrite and nitrate, are inter- convertable among themselves depending on the quantity of oxygen in the pond water. When there is insufficient oxygen or there is no oxygen available, amnionia and a large quantity of nitrites appear in the water. Ammonia is also liberated when oxygen concentration becomes low while there is a large quantity of organic sub- stances, particularly proteins, in the water. This occurs as a result of decomposition of proteins into ammonia by the action of bacteria in the water. This occurs especially easily near the bottom of the pond. The concentration of ammonia nitrogen in the eel pond water is between 0 and 13 ppm and usually between 1 and

3 ppm or lower. When ammonia concentration exceeds certain limits, it becomes harmful against eels, and the limit concen- tration varies depending on the pH of the water. Against a shirasu-unagi, 20 ppm of ammonia is quite harmful, but 250 ppm of ammonium chloride is harmless. The latter is fatal at 500 ppm. k;ainst a killifish, fatal concentrations (of ammonia)* are

■•■••••••••••■•■•• •IIII * Translator's Note: Added by the translator. Possibly (of ammonium chloride). - 117 -

10 ppm (pH 9.2), 80 ppm (pH 8.2), and 400 ppm (pH 7.1) in 24 hours and a half.* Although no irregularity in a food intake is shown up to 10 ppm, already at 2.5 ppm, it shows a sign of decrease of growth rate and of oxygen consumption. The oxygen consumption of eel increases between pH 6.2 and 7.4 and decreases at pH 8.4. The oxygen consumption of eel decreases at pH 7.2 when ammonia nitrogen concentration is between 10 ppm and 30 ppm. Phosphate: Phosphorus is one of the most important components in water that have an influence on not only the growth of the phytoplankton but also on degradation of organic substances. It exists in water of eel ponds at concentrations between zero and 500 ppm. • The phosphorus _content tends to increase .rapidly in proportion to the amount of feed, and as described previously, its content is inversely related to the amount of total floating matter on the pond water. Therefore, when changing- water takes place, the acid** in the water increases. The phosphate concentration is also related to growth and multipli- cation of Rotifera (or Rotatoria), and this relationship is believed to be caused by elution from corps of the Rotifera worms „ •

* Translator's Note: The concentration may be 50% fatal concentration or 50% mortality within 24 hours. The way the letters are printed, it is difficult to tell which is correct. **Translator's Note:. Which acid? Phosphoric acid? Or Phosphate? 11› - 118-

Phosphorus forms insoluble complexes with iron and calcium*, but pH is a decisive factor to control their formation and decomposition. Silicates: Water in Japan is very well known for its high concentration of silicates, and the silicates are supplied mainly from feldspar, of which silicic acid is about 2/3 of the total weight, and other rock forming minerals. The silicates are deeply related to the growth of Diatomaceae, and when Diatomaceae grows rapidly in certain seasons, silicates are consumed and their concentrations in water decrease. Eel pond water usually contain silicates at 16.67 mg/l. 2. Biological Characteristics Color of Pond Water: The eel teChndlog-Lsts place the greatest emphasis on "making water" in order to raise productivity of the eel, and they judge the water quality by the color of water. The water color is indeed one of the best indicators /59 to express the suitability of pond water for eel culturing. Although the eel pond water shows a characteristic bluish- green color, the color is solely dependent on the phytoplankton in the water. The plankton includes Micros sp., a species in VIxorhzceae, and it is commonly called "blue-powder". In certain areas, Oscillatoria sp. is the major plankter in the .

* . Translator's :Note: Perhaps this should read "Phosphoric acid forr: insoluble salts with iron • and calcium." - 119—

water. The color with particular hue, characteristic of a pond, varies from a pond to anothar, depending on the kinds and amounts of other phytoplankters coexisting with these two major plankters. When the "changing-water" takes place in abnormal water, the water color changes very rapidly from greenish pond water color to brown or dark brown within a very short period, and this occurs when the phytoplankton disappears rapidly for some reason, and the zooplankton, mainly Diatomaceae, appears in a large quantity within a short period. The water color also varies from place to place. Generally speaking, in Kawajiri area ând Hamanako area, the color is basically green, in Fukuda area, mostly dark green but varies considerably, and in Mie-prefecture, greenish- brown. The hue of pond water varies depending on the species of the phytoplankton, and Oscillatoria sp., particularly 9Scillatoria, Microcystis, Chroococcus, and Anabaena are responsible for brilliant green color, but green algae, particularly Scenedesmus, make the green water color darker, and Diatomaceae does so even more deeply. Thus the kinds of phytoplankter and their relative quantities determine the color of the eel pond water. Growth and species composition of the DhytoDlankton are also deeply related to the salt contents in the water, and generally speaking, salt containing water hardly becomes light, brilliant green but tends to • become brown. This tendency is particularly strong when the

s're ,17fMe.r,,A,-,3reeen,cm«rt. ml-J7Nr=-m - 120 -

water temperature is low durihg the winter. • Plankton in Eel Culture Pond: The plankton in eel culture pond is usually phytoplankton but when the water goes through the changing-water, it becomes consisting mainly of zoo- plankters. The major species included in phytoplankton in the pond may be divided into the following four groups.

1) Microcystis SD, is the major species of this group and Microcystis aeruglnosa and several others of this genus are included. Size of the colony is between 50 and 800 2) Mainly Oscillatoria sp. and this group multiply very well from the end of the summer to autumn, and when they grow well, the pond surface looks as if it is speckled, and speckle is often called "cloud" or "tiger-speckle". 3) Scenedesmus

rr a . is no very ,lortz pe,riod throughout the year except in winter. It develops color resembling to that of Microcyris sp during the summer. 4) Nitschia sp.and Cyclotella are two representatives of Diatomacea which shows basically brown color. They are often found in ponds with high salt concentrations. According to the survey made in eel ponds in Mie- prefecture, the zooplankton in the ponds consists of 11 species of Ioda, 3 species of Cladocera, 17 species of Rotifera (or Rotatoria), 1 species of Mvsidacea, and 5 species of frotozoa. The pond water had chloride in a range between 0.252 o/oo and 12.928 o/oo. Most of the ponds had it between 1 and 2 o/oo, and this croup was abbut 40% of all the ponds,

Terer.e.M1. -‘77,M=r7-.,',7X.V'Mflre`ej - 121 - followed by a .group with 2 to 3 o/oo in 23%, group with less than 1 o/oo in 11%, and 3 to 4 o/oo group in 10%. (Fig. 22) /60 The ponds in this prefecture are characteristic because of /61 their high salt content, in comparison to the ponds in Shizuoka and Aichi-prefectures. The zooplankton in these eel ponds with mountain stream water consists of only 1 to 10 species of plankters, and about half of the ponds contain only 2 to 4 species. When the salt contents in pond water increases, its species composition decreases and simplyfied. Comparing to the fresh water lake or ocean, the mixture ratio of plankton ià simple. The phytoplankton consists of 20 species of Oscillatoria sp., 56 species of green algae, 110 species of Diatomaceae. The two former genera consist mainly of fresh water species and the last mainly of salt water species. The first listed genus is most widely distributed and the two latter are not very common. Chloride concentration at 5 o/oo is the upper limit of distribution of Oscillatoria sp. and green algae, and smaller the salt concentration in water is, the larger the number of species found in it is. In fresh water ponds, Moina dubia, Brachionus Br. auadridentatus, Br. anpularis, Br. urceolaris calyciflorus,

and Keratella vala are - most widely distributed, and Mesocyclus leuckarti, Thermoc imlops taihokuensis Cmloos_vicinus, Alona rectanula, Bosmina low7irostris, Keratella cochlearis, updrata, nia lonrriseta, Polyarthra trizla, AsnlauchnoEus

Ceratium hirundinella and othersare also found commonly. - 122 -

In fresh stream water ponds,

Sinocalanns Psertdodiaptomus inopinus, Paracyclo- Keratella crucifor- pina nana, Neomysis japonica, Brachionus plicatilis, mis var. eiclizaaldi, Testudinella clypeata, Pedalia funnica, Balanus nanplins larva are found, and Sinocalanus, Pseudodiaplomus Neomzsis and

Br. plicatilis are found most commonly and in large quantities. In the sea water ponds,

Acartia spinicauda, A. iscana, A. tsuensis, Oithona nana, Ceratium maeroceros, C'. furca, FayeIla ehrenbergi, Tintinnopsis radix are found but their quantities are small. As the phytoplankton, Microcystis acrugiziosa, Chroococcus dispersus, Merismopedia tenuissinza, Coelosphaeriuni kuetzingianum. Phormiclium tenue, Oscillatoria tenuis, Chroococcus limneticus, Synechococcus sp., Se- lenastrunz gracile are commonly found, and in high salt ponds, Chroococcus dispersus, pinechococcus si., and Phormidium tenue, and Selenastrum Eracile of green algae, and Cz2lotella El2merata, MeneEhiniana of Diatomaceae are long lasting species, and large quantities of these same plankters appear in the same ponds annually. Their quantitative distributions in summer* are particularly abundant. The species in Oscillatoria sp. are the most popular ones in summer and Hicroczeis aeruzinosa, /62 MerismIpedia tenuissima, M. punctata, Chroococcus limmetens, C. minmtus, and Coelosphaerium kuetzinganum are representative. Scendemaceae, Oocztoceae, Micractiniaceae, Dictdosphaerium and Coelastrum are popular green algae in summer.** Although

*' Translato .r's Uote: Added 1) , the translator. ** Translator's Note: Added by the translator.

7■7 Chaetoceros similis frequently appears during summer* discon- tinuously, 'Diatomaceae is not partictilarly popular:in ,summer*. In winter season, Chetoceros disEersus, Szpechococcus sp., and Selenastrum gracile, which are somewhat specific species as described previously, are mixed with a representative species, Chaetoceros muelleri. Seasonal Change of Plankton: Seasonal variations of species and quantity of the plankton are quite remarkable. Although the vegetable plankton has the larger .proportion than the animal plankton throughout the year, the latter increases from fall to winter, and becomes maximum in winter. The latter's variation in quantity is between 0.7 and 2.9%. As to the seasonal change of the species, Cladocera- appears in a largest quantity in spring, followed by Rotatoria and - Cobepoda 'appears in the -smallest amount. But in the other three seasons, summer, fall and winter, Rotatoria appears in the largest amount followed by CopeEeda. Rotatoria indeed appears most frequently and in the largest amount throughout the year, but Barachionus bakeri is the most representative species of them all in winter, Polzarthra 2. .1atyptera in fall, and Pedarion mirum in summer. Although Anuracea cochreoris var , tecta appears in summer also, it - is found most frequently in October to December. (Table 11) .- C22e2oda shows up most frequently in winter, and Cladocera, specifically Noina weismani and Chvdorus ovalis are • quite common in both spring and fall. Diaphiln2soma appears - 124 -

only in fall in a small quantity. • The phytoplankton is always the dominant species in normal pond, and decreases slii.ïhtly in proportion during winter. LyxoEllyceae is - the representative genus of the phytoplankton during summer and fall, while the quantity of solar radiation is large. Among the species in this genus, /63 Microcystis aeruginosa, M. flos =aguae, Oscillatoria limosa, and Anabaena sniroides are representative species. Microcystis increases early in the spring when the quantity of solar radiation increases, and reaches the maximum in September and decreases later. The optimal temPerature for the growth of the plankton in this genus is between 21 and 26°C. Anabaena has the peak population in summer.

Diatomaceae multinlies in winilpr nn(i decreases in spring, and Scenedesmus ruadricanda is the representative species. (2) . Phenomenon of Changing-Water The phenomenon of changing-water, "mizu-gawari", is a sudden change of color of water of the pond, which is used for rearing various kinds'of temperate fish. In an eel culture pond, the normal color is bluish-green - the traders usually use the, color of a broad bean (or horse bean or straight bean) as a standard - and it changes quickly to dark brown, yellowish brown, yellowish green, milk white or nearly transparent, . within a short period. When this occurs, the eel does not

take feed, and starts to do "hana-age", and at times, a large - 125-

number of eel in a pond die. It tends to occur in May and June, or the rainy season to early.in summer, and September • and October. The former season is the more dangerous season, and extent of the damage is usually larger. Therefore, predic- tion and prevention of changing-water are the most important problems to be studied in the eel culturing technology. (Fig. 23 ) In a normal pond, the composition of the zooplankton is about 0.4 to 2.9% of the total plankton and that of the phytoplankton is 97;l to 99.7%, but after a changing-water, the composition of the zooplankton is at least 23%, and ROtifera (Rotaforia) is the most common of the total zoo- plankton, its composition being between 56% and 47%. Increase of the proportion of the zooplankton is a sign of the changing- water. The dominant species of Rotifera is Brachionus 22, la in Kawajiri area, and B. pliçatilis in Mie-prefecture. Among the phytoplankters, the dominant genus changes from the green algae to Micropistis of Oscillatorial. after the changing- water. In Yoshida area of Shizuoka-prefecture, eel culturing ponds are classified into the following three different types,

according to the way by which the changing-water occurs. /64 I. The pond in which the changing-water occurs very frequently while ponds are being used for rearing eels. II. The pond in which the changing-water occurs only at the

beginning stage of using fresh ponds or later during the season chanes particularly in fall. • III. The pond in Which the changing-water seldom occurs.

equ';1.11!,17,MMI7i: - 126 -

When the vegetation of phytoplankton in these ponds is studied, it is found that . the type I pond contains mainly green algae and a little of Oscillatoria sp. is contaminated in it; in the type II pond, dominant green algae changes to Microcmtis of Oscillatoria sp. at the beginning of summer, and further in fall, the dominant genus changes to green algae or Oscillatoria; in the case of type III, when the dominant plankton is Micromstis, the water is most stable but some ponds contain green algae only or a mixture of green algae and Microcmtis; and some of the type III ponds contain the same vegetation as described in the type II. Of all these three types, the type II pond is the most common one, and type III or a mixture of type III and type II is also frequently -eneouni,ered, forlunat,ely, there-are-only,a „small number of type I ponds. Microcystis multiplies quite well in a pond, in which salt concentration is small, and the degree of its multiplication is very well related to the salt concentration of the pond water. This is an important point that every trade man using salt containing water for the ponds has to pay attention to. Namely, when the degree of multiplication of Vicrocystis is pronounced in a pond., the pond water contains Cl at less than 3 o/oo, and if the Cl concentration is above

this value, its multiplication is pOor, and it hardly ever can • be detected in pond water with Cl at higher than 5 o/oo. In - 127 -

,ponds in which the Cl concentration is higher than 5 o/oo, • the vegetation of phytoplankton is mainly occupied by very small plankters, Furthermore, frequency of the occurrence of the changing-water is smaller in ponds in which salt concentration is small, and if it occurs, it is not a serious one. However, in ponds with high Cl concentration, the changing-water occurs more frequently and more seriously. (Table 12) As probable causes of the changing-water, the following explanations may be presented. a) Chemical change of the quality of water effects the change of vegetation of the phytoplankton in the water, and the /65 -changing-water .occurs, and as a result, Cl.e zooplankton increases. h) When Rotifera feeds on the phytoplankton in the pond water, it multiplies in unusually large numbers. This is the changing-water, and as a consequence, the water quality becomes abnormal. c) DaEhinia bulex feeds on the phytoplankton and causes the changing-water. • d) When there is a sufficient quantity of nutritional mineral components in the water, lack of carbon dioxide'is the cause. e) The changing-water that happens rarely in December to April, when the water is cold, is caused by ciliata. Tining of Occurrence and Duration of Changing-Water: Changing- water occurs near Hamanako in two seasons between May and - 128-

June and between September and November. Particularly the one that occurs in May to June causes quite serious damages. In Mie-prefecture, particularly near Tsu-city, the changing- water occurs quite frequently between May and October when water temperature is between 17 and 20°C, but it never occurs between January and April. The changing water caused by an abnormal multiplication of Rotifera lasts at least for 4 days and sometimes as long as one month, but the average duration is between 7 and 14 days. This period is approximately the same as the period of one multiplication cycle of Rotifera. The one multiplication cycle period of Rotifera is quite short in summer when the water temperature is high, and it is short at the beginning of summer and fall when the temperature is gl, not very, .high, The one.s that occur in .illU,,,summer between JUly and August repeat many times in this season, because they occur quickly and suddenly but complete in a short period. Consequently, the whole proceeding of these changing-water appears as if they are continuous for a long period. Prediction of Changing-Water: As a method of.predicting the changing-water, two methods, one biological and the other physico-chemical, have been applied. The former is based on the relationship between abnormalities in behavior of eéls and proceeding of multiplication of Rotifera and the latter on the relationship between abnormal behavior of eels and change of water quality of the pond water. 4IM a) Biological Iethod.- When the size- of individual Rotifera becomes large, the number of feieale individuals with summer - 129 -

eggs increases, each holding 3 to 5 eggs or more, and the number of total Rotifera is larger than 10/cc, and in addition, when the vegetation of the phytoplankton is represented mainly by micronalLae and its quantity is large, changing-water is about to occur. The multiplication coefficient y can be obtained by the following equation. • y 1 log Nt 11; 'Where, the number of individual Rotifera (number of bodies/cc) at time to (unit, day) is shown by N o ; the number of individual

Rotifera at time t is shown by N I and loge 0.4343. If the y value is 0.3 or larger, then the intensity of the changing-water may be more serious than "hana-age", and if it is larger than 0.5, some eels may die, as a result of the serious changing-water. . When the y value is actually obtained by calcula- tion, the number of days remaining before the changing-water takes place can be estimated using figure 24. (Fig. 24) /66 When the number of Rotifera holding more than 3 to 5 eggs is larger than usual, then'the multiplication proceeds faster, and therefore, the changing-water may occur sooner. If there is a chance of weather change, a particular caution is needed. If proportion of small individuals without summer eggs becomes larger, the content in the digestive system is - 130 -

nearly colorless, number of eggs held by one adult Rotifera is only one, or number of females holding sustenance eggs increases, then the Rotifera in the pond completed its multi- plication cycle. Under these conditions, the pond water is recovering from the changing-water. Other symptoms of recovery from the changing-water is appearance of the phytoplankton, specifically Chaetoceros similis, Micractinum pusillum, and Coelastrum microporum, in the water. b) Physico-Chemical Method - Although the amount of dissolved oxygen in a pond, degree of transparency of pond water, and change of water pH are useful signs of the changing-water, they are not very accurate in prediCting the changing-water. The reasons are as follows. When the amount of phytoplankton remP.ins smR11 4 even if it changes nonsidprphlyi the change ig not exactly reflected on the degree of transparency of water. On the other hand, more serious changing-water occurs in a pond that contains a large quantity of phytoplankton on which Rotifera feeds. Therefore; at the initial period of the changing-water in this type of pond, even when Rotifera starts the cycle of multiplication and feeds on the phytoplankton available in quantities, decrease of the phytoplankton cannot be reflected on the degree of transparency in direct proportion. Change of the water color is not remarkable unless the number of individual Rotifera increases drastically. There is no - noticeable change in pH and soluble oxygen quantities at the • 'initial period of multiplication cycle of Rotifera, These - 131 -

physico-chemical factors are also under the strong influence of weather. In conclusion, the biological method, which examines the conditions of multiplication of Rotifera before serious environmental changes detectable by.the physico- chemical method, is useful in predicting the date of the changing-water and the degree of its seriousnesS, and also in judging the proceedings. .Measures to Counter Changing-Water: It is important to predict occurrence of a changing-water well in advance and to continue the observation as to the proceedings of the changing-water. When a changing-waier is predicted, the cause, multiplication of Rotifera, must be countermeasured. That is, the .r,apidy multi_plYig_Rr‘tife -ra must be fiectrnyPA or itq multiplication must be stopped. Whatever method is used, application of the method Should not harm the eels and the phytoplankton which is the source of dissolved oxygen in the water. It should destroy only Rotifera. The traders in Hamanako area usually introduce seawater into their ponds whenever they see some abnormal change in the pond water, and they have been tremendously successful in checking the irregul.arities of the pond water. This procedure is based on their experience accumulated in many years, and the method is effective in destroying Rotifera. Fatal concentration of bleaching powder, cupric sulfate, slaked lime, seawater, and fresh w,er aGainst Rotifera are listed in table 13. (Table 13) - 132 -

Among all the listed chemicals in the table, the most effective chemical .without injuribus effects to eels and the desirable phytoplankton is bleaching powder. The effect of bleaching powder (chloride of lime) against Rotifera is fast acting and strong. The traders in the eel culturing business are thoroughly aquanted with its use, as they use it also to remove ikari-mushi*. As the lethal concentration of bleaching powder against Rotifera is much .smaller or less than 1/6 of that against the eel and carp fish, it is quite a safe chemical in destroying. Rotifera. Rotifera usually stay at the bottom of ponds. wIlen the sky is clear and the amount of solar radiation is large, but Comes up and stays on the top surface when the sky is cloudy or it is raining.

Ulrarefore,, the chemical can be_applied_most effectively Aml cloudy days when the water is calm. The fetal concentration of chloride against fresh water Rotifera, Brachionus cflzciflorus and Br urceolaris, which appear in Hamanako area is 5 9/00. Although both sea water and fresh water are effective in destroying Rotifera, practical use of them is always accompanied by some difficulties. Namely, when fresh water is introduced into a pond with high /68 salt concentration, it is often accompanied by subsequent death of the phytoplankton, and pouring sea water into a fresh water pond is accompanied by the same maleffect of destroying phytoplankton and general deterioration of the pond water. On the other hand, if bleaching powder is used, then

* Translaborss Note: Literally anchor-worm. See Chapter 8. - 1 33 -

the subsequent rapid increase of favorable phytoplankton takes place quite often. • Dipterex* which has replaced bleaching powder as a more effective chemical to destroy anchor-worm, is certainly effective in terminating Crustacea at 0.2 to 0.3 ppm, but its lethal concentration against Rotifer. a is between 5 and 15 ppm, and the concentration at which its multiplication is interrupted is between 2.5 and 10 ppm. In addition to the chemical method described above, a mechanical filtration device, which collects the zooplankton, mainly Rotifera and return the phytoplankton into the pond water, has been used quite successfully. As a natural enemy of Rotifera, sword-Da2hnia pulex has been known. The traders usually take the following procedures as a measure of prevention of the changing-water, and all these are based on the afore-described principles and therefore, appear to be sound. 1. If the "blue-powder" is dead and floats up to the water surface, it is to be drained off from the pond or to be scooped by a net when it gathers at a corner of the pond by wind. 2. When the zooplankton starts to multiply, to spray Dipterex and disinfect the pond water. 3. To spray calcium hydroxide and improve the quality of • the bottom sand.

* Translator's Note: See, for example, in Merck Index. - 134 -

4. To drain off the bottom water, - and add fresh water. • 5. 'To expose the pond water to air by a stirring device. 6. To change water - completely.

3) Bottom Soil Water cluality and Quality of pond bottom soil are inseparably related to each other, for both of them are basic environmental factors to determine the well being of eels and other aquatic animals. Through these two basic media, organic and inorganic substances, which are nutritional source of aquatic animals, complete the cycle of material exchange. Whether the bottom soil is needed in an eel cultur- ing pond or not was one of the major problems discussed in the field of eel culture technology around 1910. It had been concluded that although there were a number of good reliable examples in which eels grew very well in a concrete water bath, it is preferable to have bottom soil for the reasons that it promotes better balanced environment more accurately and cheaply, and that it matches with the eel's habit of smuggling itself into sand or mud. Since most of the eel culturing ponds in this country have developed along the coastal line and close to it, the bottom soil of ponds is basically either sand or clay. It has been, however, converted to either clay or humus loamy soil after many years of eel culturing as a result of cumulation« and decay of corps of the plankton, excrements of eels, and residue of feeds. • A large quantity of these material deposits on the - - 135

bottom of the *pond, but majority of that is either washed out or mechanically removed at the.time of annUal pond cleaning. /69 Accordingly, in Hamanako and Yoshida areas, it is very seldom that the depth of the bottom mud exceeds 20 cm in a pond of which the bottom soil is basically sand. It has been known that as far as the depth of the bottom mud is less than 6 cm, the yield of the pond increases in Proportion to the depth of the mud, but if the depth is more than 7 cm, the yield decrease s . are some ponds which though slightly. However, there certainly

exceed 20 cm of depth and yet prove an excellent yield. There- fore, the more important factor appears to be the quality of mud. If, however, amount of floating mud increases, then the yield lowers. (Table 14) It is quite natural that a large quantity of organic materials precipitates at the bottom of an eel pond, into which highly nutritional feed stuff is thrown, and the amount of this precipitation is deeply related to the produc- tivity of an eel pond. The amount of organic substances, actually determined by the standard combustion analysis, is as follows. (Table 15) In both areas, the contents of organic substances are between 5 and 1 5 1 and ponds with organic substances between 5 and 10; are most frequently found, Of all the ponds • tested, the ones with less than 55 of organic matters tend to - 136-

show very unstable growth of the plankton and variable • composition of plankters, and the changing-water occurs in spring and fall or quite often throughout the year. As a result, the feed intake of the eel is also quite uncertain, and meat increase of eel is, of course, poor. On the other hand, if the content of organic matter is too large, then . the pond is usually quite deteriorated or poorly maintained, although the plankton composition changes very little If abnormal accumulation of sulfide occurs in addition to a large quantity of general organic matters, then eels in such a pond frequently do "hana-age" and difficultly feed. As seen in all these examples, the content of organic matters in the bottom soil of eel ponds and the yield of the pond are very deeply related. If the yield of a pond is good, feed quantity thrown into the pond is alsO large and so is the amount of excréments, These cause multiplication of the plankton in the pond water. Corps of dead plankters also precipitate at the bottom. The difference in productivity between Kawajiri area and Hamanako area shown in Fig. 25 is caused by the . difference in management system, environmental factors, and level'of. technology in these two areas. (Fig. 25) The organic matters in the bottom mud are decomposed by bacteria, and are eluted out into pond water as an additional source of nutrition to other living oranisms and animals.

- - 137 -

When these degradations do not proceed smoothly, the pond • water usually contains salts in a too high level; the lower layer of water stands still without much circulation, and the water temDerature is also low. In these cases, the yield of eel production is usually poor. Color of the bottom soil varies among black, . reddish yellow, yellowish green and other complicated hues, but the color and hue are not at all related to the productivity of the pond. When the pond water temperature remains between 23 and 31°C, temperature of the bottom soil is 2 to 300 lower than the water temperature, if it iS above 30°C; the bottom soil temperature is 1 to 2°C higher than the water temperature, if it is below 25°C; and the bottOm soil temperture is on1y 1°C or so different from the water temperature, if it is between 25 and 30°C. Bottom soil pH varies between 3.2 and 8.4 and if the soil basicity is higher, the productivity is also higher. Occasionally, however, quite acidic bottom.soil is found, even when the pond itself is maintained under very good conditions. If the acidity of bottom.soil is too high, then the soil is harmful to eels. When pond water and bottom soil become strongly acidic, growth of the pond water plankton becomes poor and the eels' appetite deteriorate. Reouired conditions for the bottom soil of eel pond are appropriate water-holding capacity and permeability - 138 - against water. The size of soil particle cavity varies depending on the kinds of soil.* Water-holding capacity of soil is deeply related to this soil cavity, cohesive power, viscosity and adhesive power of the soil. The cohesive power is the power by which soil particles cohere - together.. The adhesive power is the power by which soil particles adhere to other materials, and although this power is stronger if the soil contains a larger amount of clay, it is weaker if the soil contains a larger amount of humus. However, if humus is dried, its adhesive power increases. In terms of physical characteristics of soil, both sand and conglomeratic soil have poor water-holding power, while clay cannot retain any stable bottom shape, and therefore, these are unsuitable as a bottom soil. Generally speaking, clay which contains sand between 30 and 40% of the total mixture soil is most suitable for the pond bottom. Regarding the relationship between the productivity of pond and the content of organic matters in the bottom soil, a pond of which the bottom soil contains more than 50% of sand particles has a far better productivity than ponds of which the bottom soil consists of other types of soil but contains a far larger amount of organic matters. il ) Structure of Pond (1) 'Size of Pond

Trunslator's otel In these sections of the chanter, parat;raphing does not seem to be too well done, but no change is made by the translation.

• • - 139 -

One of the most important factors which determine the size of one pond and number of ponds that can be operated is quantity of water, particularly that of underground water available. The size and number of ponds to be built also vary depending on whether the culture stock rearing is also done in parallel. In principle, if the quantity of available water is abundant, the business scale can be large, enabling the operation of a large size pond and a large number of ponds, but if the water quantity is limited, then the size of the pond should be small and the number of ponds should be restricted to a manageable level. During the process of development of the eel culturing business, the ponds built in early stage of this business, particularly the ones built before 1910 1 had a 2 surface area larger than 9,917 m 1 but it was later found that these large ponds had lower yields than smaller ones and manag- ing -large ponds was also more laborous than managing a number of smaller ones. The recent trend is to build a smaller pond, usually around 31305.8 m2 or any size larger than 165.3 m2 and make a large number of these small - ponds. In the table shown below, sizes of ponds built before and after the war in Yoshida area of Shizuoka-prefecture, are listed. These figures illustrate the trend of the size of ponds.

(Table 16) 2 amely, before the war, the smallest pond was 826 m 2 and the larcest m , and the average size was • pond was 9,917 - 140 - between 2,644 ànd 6,611 m 2 . The ponds with areas between 3,926 2 • and 5,289 m occupied about 50.3% of the total number of ponds. The ponds newly built or modified after the war are generally smaller, the number of ponds larger than 3,967 m` decreasing_ while the number of ponds smaller than that, particularly 2 smaller than 2,644 m increasing. The size of pond is quite closely related to the yield per unit pond area, and generally speaking, the larger the ponds are, the smaller the unit yields are. Therefore, /72 _ 2 2 it is preferable to build two 3,306 m ponds or one 3,306 m 2 2 pond and two 1,652 m ponds instead of building one 6,611 m pond, if the water supply is sufficient. If the water supply is not abundant, it is more practical to build 4 ponds with areas between 1,652 and 1984. m2-- -the size to be determined according to the amount of water available to one pond---. Although, of course, expenses for building ponds and labor cost increase if many small ponds are to be built and managed, but, if prevention of diseases and other factors are taken into consideration, the above-described disadvantages are really not serious problems. In fact, a large size pond is useless especially in an intensive eel culture pond, because when distribution of eels in a pond is examined, it is found that they are most densely distributed along the pond wall within

1 m from the wall, and fairly densely within 4 m but very rarely more than 5 m away from the pond wall. In many cases, eels are found along the pond wall, near the feeding post and - 141 - in the shade. They may be found in the central part which takes the largest portion of a pond or along the bright side of the pond near the wall only when the water quality deterior- ates or the amount of soluble oxygen decreases during the night, as the eels distribute themselves in a wider area seeking more oxygen in the water. Lately water spraying by stirrer has become quite a popular method of supplying oxygen into a pond, and there is no doubt that other methods and devices will be presented and modified for practical use in improving the rational use of pond water. Therefore, based on these facts,'it can be concluded that the future trend is to use a Small size pond and produce the eel quite intensively. ie%\ Ct,, 1,c.; .L).1.u.-)11alie,E114u.. 1011 It is important .to select the site of the pond before starting building it. The ideal site is a place where wind blows very well and amount of solar radiation is large, and direction of the pond is also to be designed to meet these ideal conditions. It is also important to find the building site at a place where transportation is convenient for purchasing feed and marketing the eels, where the land is cheap, where the needed water is available abundantly, where there is no farm land that requires spraying various agricul- tural chemicals nearby, and where the land is slanted slightly for convenience in draining a pond. It is, of course, extremely difficult to find a site where a il these condit:,ons are ful- filled. Therefore, the most important condition is suitability - 142 -

of the site for management of the pond. The basic shape of the eel pond is a rectangular form, but it quite often occurs that the shape of the pond must be altered to square or various other shapes to suit the layout of available land. Generally speaking, however, a rectangular, diamond or long oval shape is preferable. Water at four corners of a pond is difficult to fresh up, and mud and various residues tend to accumulate at the corners and decay there. Besides, even if fresh water containing a large quantity of oxygen is poured, the water at the corners is difficult to be freshened up. These corners are called a dead point in the civil engineering term. It is important to try to reduce these dead points when an eel pond

1-214- • -Lb •;n41.-.1., U, (3) Water Depth There has not been any definitive theory proposed as to the desirable depth of water in an eel pond. Most of /73 the eel ponds built in the past, however, have 1.0 to 1.5 m of water depth near the drainage and 50 cm to 1 m near the flooding pipe. The water depth has its local character, depending on the area, deeper in Hamanako, Aichi and Mie areas and shallower in Yoshida and Yaizu areas. Seasonaly, the ponds are made deep in winter and shallow in spring. In an eel pond, the water contained in it can be classified into the following several layers. A nutrition- • formation layer is the upper layer I'vhere the phytoplankton is - 143-

distributed, producing oxygen and absorbing nutritional • substances from the water. Corps of the dead plankton gradually drop down to the lower layer from the water surface, and decompose by bacteria. Carbohydrates produce water and carbonic acid, and proteins yield ammonia via simple amino acids. Ammonia formed is oxidized by nitrate bacteria to NO or NO These decomposition products remain in a lower 2 3' layer as colloids or as ionic salts. In this layer, oxygen is . consumed, and this layer is called a nutrition-decomposition layer. Between these two layers, the oxygen content in the water is. greatly different, and consequently it is called a jump layer. Generally speaking, the oxygen content in the surface area never reaches a supersaturation stage, but on .the lower .end of the upper surface, dt..is under supersaturated concentration. The water layer in which the oxygen content is at the maximum is called a. critical layer. The layer in which the concentration of oxygen produced by anabolism in the nutrition-formation layer and that of oxygen consumed in the nutrition-decomposition layer is balanced. and is called a compensation layer. In an eel pond in which the phytoplankton grows abundantly in the surface layer, the sunlight does not reach very deep into the water. The degree of transparency of water, in terms of depth to which the incident ray can reach, is determined using a white plate, The transparency is approximately proportional to the amount of suspended matter in the water, th ,_3t is, amount of phytoplankton in an eel pond.

O The transparency of eel ponds usually is 30 cm when the water - 144-

is fairly well made or about to be made to satisfaction, between • 25 and •30 cm in most of the ponds, and 20 cm in a pond in which the "blue-powder" is very well made to grow. Depth of the compensation layer is usually between 1.5 times and twice as deep as the transparency depth, and therefore, in normal eel ponds the compensation depth is between 30 and 40 cm to between 45 and 60 cm, as the transparency depth is between 20 and 30 cm. It appears, therefore, that the water depth of intensive eel culture ponds may be best made equal to the compensation depth, because then the balance of oxygen or the degree of supply of oxygen from the surface layer to the bottom layer in which the oxygen is required, is assured. Since the compensation depth is nearly equal to • the .shallawest water depth which usually ,is the mater_depth at the water inlet, the water depthl usually determined by the traders using common sense, is scientifically satisfactory. The water depth may better be controlled corres-' ponding to the changing depth of the compensation depth rather than by routine seasonal adjustment. It should also be taken into consideration that concentration of the phytoplankton can be adjusted not only by controlling water depth but also by pouring fresh water or draining the pond water. Lately, by bubbling air through the pond water or by mechanically stirring water, it became possible to disperse the oxygen nearly saturated on the upper layer or supply • oxygen into the pond water. Using the present day facilities, - 145-

however, the area of pond that is affected by the stirring or /74 110 bubbling is somewhat limited. If equipment which serves for a wide range area of the pond is used, then the water depth could be made larger than the compensation depth. Regarding the draining of the pond water, if the pond bottom is slanted along the straight line connecting the water inlet and the drainage, the draining becomes quite efficient. However, if this slant is made not only for the convenience in the draining but also for equal distribution of the oxygen in the pond, then deeper pond can be operated. In other words, if a half area of the pond is made equal to or shallower than the usual compensation depth, and the other half deeper than that, then by natural or mechanically assisted • flow of water would distribute the oxygen equally to the water in the deeper ,area of the pond also.

(4) Structure of Pond

Pond • Wall: The height of the pond wall is sufficiently tall

if it is about 50 cm. The eel cannot escape from the water

surface if the wall is as high as about 1/3 of its body length,

and there is no need to attach "kaeshiu* to the pond wall, if

the wall height is 50 cm over the water surface. In fact, the pond wall should be as low as possible, because if the pond wall is higher than the water surface, then the wall makes itself an obstacle for wind, which is extremely important and valuable when the eels do "hand-age" or at the time of changing- water.

* Translator's Note: Transliterated. Literally "returning". Èerhaps a wire-net or board attached to the top of the pond wall at an angle to prevent an eel from jumping over the pond wall. - 146-

The wall can be made with concrete or if large • size stones are available, as in the Kawajiri area, it may be built with the stones and filled and fixed with cement. In place of these semi-permanent pond walls, it can also be built with a thin concrete plate or wooden board. In recent days, because of high price of the wooden board, wood walls are seldom built. The upper- surface of the dyke is called numa- fumin* and the major dykes are built wider. The width must be sufficient in transporting feed, and it is built with soil scraped out of the pond bottom at 20 to 30 Cm depth. Water Inlet and Drain: The primary condition required in designing the water inlet and outlet is speedy 'pouring and draining of water. Since the water flow is quite large close to the.e inlet and outlets,, the 1Dottom_in this ..a2ma,must built with a concrete layer with sufficient thickness. Since the eel has the rheotaxis nature, there must be an attached screen net at the water inlet. The water is usually poured in at dawn or at the eels' "hana-agen. It is important to design the position of the water inlet so that there is no dead point in the pond. In order to increase the efficiency of oxygen supply, it is also preferable to give a sufficiently high head between the water inlet pipe and the pond surface. • In recent years, the water supplied is mainly underground water, and therefore, a water inlet Epte is not

e Trnslator's Note: Literally "horse-stepping". - 14? -

needed, and instead, a pipe is used to let fresh water fall • into the pond. In this case again, the position of the water pipe should be on the diagonal line including the drain, and the head length should be sufficiently high. If these cannot be achieved, it is preferable to let the water from the pipe be sprayed on the pond instead as one stream of water from the Pipe. The metal screen net at the water inlet and outlet gates is built with brass bars, copper lines, and pine or Japanese cypress wood. Using cypress or pine boards, the upper half of the gate is boarded, and at the lower half, brass bars with 0.3 cm diameter are lined vertically at about

0.2 mm intervals, and connected with No. 20 copper lines, or • they may be welded, and horizontally, brass bars are lined at 10 to 15 cm intervals. Since the whole water pressure acts at this metal part when water is poured or drained, the gates must be designed and built very carefully. The dam-board is either cypress or pine and about 3 cm thick, Its construc- tion is relatively simple at the water inlet, and it is important only to be able to control the amount of the pouring water easily. At the drain gate, either two boards are placed and sand packed in the space between the boards, or only one board is lifted up or lowered using a screw-bar. In the latter case, since the water pressure of the pond works on this single

board, two thinner wood boards are attached on both sides, and particular attention has to be paid to occasionally observe the • degree of decay of the board. • - 148 -

At the outside of the drain board, a large earthen- pipe is blaced and its one end is pierced through the pond wall to reach just outside the drain board. The diameter of this pipe varies depending on the size of the pond, but it is usually between 35 and 50 cm. At the outside end of the earthen-pipe, a space sufficient to allow two workers to work bending forward, is provided. Feeding Post: Position of the feeding post should be about the centre between the water inlet and outlet. That is to ' say, if the pond is rectangular, the feeding post is in the middle of the longer side. Since the eel likes shaded areas according to its nature, the feeding post is better situated on the s4 d1., whir.h is .hederl f^ -c en all dey period. Thi s is also a useful consideration because the feed can remain without decay for a longer period. If the pond wall faces the south, and the feeding post was to be placed on this wall, not only the residual feed tends to decay faster but also the eels are not comfortable because it is too bright along this side of the wall. The spot where the feeding post is to be placed could be bent inward into the pond with a smooth large curve, and at the same time, the wall height may be made lower. These considerations are useful in expanding. the feeding surface. It is also quite efficient to build a feeding post separated from the pond wall, by erecting stakes in the pond • nd placinL; boards from the pond wall towards the centre of the pond.

17,t 77,7. - 149 -

The pond bottom around the feeding post is better 111, to be made up with ballust or gravel in wide areas. When eels are to be caught by a net if the bottom soil is soft mud, not only the work is hard to do but also the water is badly polluted with floating mud. Since the feeding post is the place where the eels gather and swim very actively, unless the bottom around it is protected with ballust, it is often dug deeply. The protected bottom is also useful when the feed .residues are to be removed. Feeding shed may be built in three different types depending on the requirement. One is a combination of the dwelling of the pond guard and his family; the second is a simple hut to serve also as a rest room for the pond guard;

II› and the third is ,strictly_for.bandling .the_fed.. In the fiT'st /7 type, a feeding post may be built in the garden of the dwelling entirely separated from the house, but in most of the cases, a corner of the house is extended to the end of the pond wall, with cement floor, and at one corner of the area, a cooking stove is built. The size of the house in.these cases varies depending on the circumstances, some being permanent houses, others temporary shacks. • • In the second type, a hut with areas between 2 2 16.5 m - and 19.9 m or rarely as large as 33.1 m is built. inside the hut, the floor is a cement floor and at one corner, a large cooking stove for cauldron is built, and one of the sides is used as a feeding post, while the other side is one • in which a caretaker can rest or sleep. or two small rooms - 150 - • The feeding area of these huts is often extended over the pond surface as far as 6.6 m, and the huts are often darkened by boarding the windows.

• (Fig. 26)

(5) Accessory Facilities

Rest Area: In the past, an open system, so-called "kake-

nagashi"* was popular. In this system, the pond water is kept drained while fresh pond water is supplied continuously. This system is no longer used, and to replace it, a circulation system became popular. In this system, an area of pond, about 2 30 to 60 m is surrounded by boards, and sufficient spacings between the boards are provided as an entrance-exit for the eels. At the centre of this rest area, a water inlet pipe is • placed. Eome of the boarded rest -areas have a-water -drain of their own. There is no generalized shape for the rest area,

and it all depends on the invention of the pond guards, -4ie type of water inlet and availability of the water. Advantages of setting up rest 'areas for the eels

are found in prevention of "hana-age" and loss of "blue-powder" and nutritional component accompanied by each water exchange

at the time of "hana-age" and in releaving the caretakers from mental as well as physical labors.

Consequently, the yield of eels from the pond can /77 be raised.

• * Translator's Note: Literally spout-running. - 151-

When pouring water into the rest area starts, • oxygen content in the pond water increases and the water temperature lowers. Water Stirrer (Water Nover): In order to supplement oxygen into the bottom layer of a pond or the whole water in a pond before dawn, it is best to pour fresh water containing nearly saturated quantity of oxygen. As one of the methods of supplying oxygen, a water stirrer is used. (Fig. 27) The facility consists of motor, hut and water wheel. The motor is 1/2 to 1 HP, and the hut can be as small as only to protect the motor from rain and snow. The water wheel may 'have 50 to kb-O cm dliameter for ,a J. EP-motor.and-about 36 cm diameter for a 1/2 HP motor. To the wheel ring, 5 to 8 pieces of wing, usually 6 pieces, are attached and the size of one wing is 15 x 60 cm to 20 x 15 cm*, usually 12 cm wide and each wing has 7 or 8 small holes. The wheel may be rotated about 130 times (per minute)", The position of the wheel may be best if the wing stays under water while the ring remains in the air, When two ponds are built adjacent, one motor and a hut to cover it placed on the dyke between the two ponds, can operate two water wheels, one in each pond, simultaneously.

* Translator's Pote: In c.2mprehensive, • ** Translator's Note: Added by the translator. - 152 - In order to save the electric power required, the wheel should be designed to rotate very lightly. Use of automobile wheel may be a wise idea. The stirrer is usually operated before and after.the feeding in order to supply extra oxygen into the pond, but it may be operated continuously after dawn. Of /78 course it should be operated not only at the time of "hana- age" but also as a measure of prevention of the "hana-age". It is important to use it well in advance when its need is predicted so that the eels can live comfortably. Although it is ideal to operate the stirrer while fresh water is being poured, so that fresh, oxygen-rich water is distributed widely and quickly, its principal purpose is to expose the pond water to fresh air, and let oxygen be absorbed and diffused into the pond water. Operation of this vehicle is done, therefore, anytime when the conditions of pond water, timing, and conditions of eels indicate the need of it. Based on more or less the same principle, various other devices were developed. For example, compressed air is dispersed through a carbon rod, or through an air-dispersing cylinder placed over the pond and connected with airation tubes. Also water may be jetted radially through a jet placed at the centre of the pond to expose the water to the air. (Fig: 28) Artesian Well: In an ordinary well., the water surface is the same as the level of the connected underground water. The quantity of the well water is proportional to the space of the cavity between the strata supported by clay, shale or clay-slate, all of which do not let water penetrate through. Sandstone, - 153 -

gravel and tufa permit water to penetrate, and a large quantity of water remains absorbed in this strata.- When a pipe is pierced as deep as the strata, underground water can be obtained. If a water containing stratum is between two non- penetrating strata, water moves quite freely. If the land surface or underground stratum is slanted, the underground water layer also isElanted and the water runs towards the lower side. The water included in a water-containing stratum in a lower level is under pressure for various reasons, and if the water is under pressure larger than the atmospheric pressure, then the water comes up above the original underground water level, when a well is dug, and it finally reaches above the ground surface. This type of well is called an artesian well, • and it is auite often successful to dig and find an artesian well where gravel or sandstone stratum is a water containing layer and two non-penetrating strata run slightly slanted or theSr form a basin. An alluvial fan which often develops near a river mouth mostly consists of sand and gravel, and if there is a non-penetrating stratum-like clay, then underground water can be obtained from a shallow well. This is indeed the type of well used in Yoshida area, near the river mouth of Oigawa. The quqlity of water from the artesian well is different depending on the soil strata that the water has to pass through before it reaches the surface, the type of water containing stratum, and the velocity of water movement. The better water is fast movinr: water with little organic matter. The • w„, -;,er is usually clear and transparent and its temperature is - 154 -

low. There is not much difference in . its water quantity and • temperature throughout the year. Some underground water lias in it, and other water contains iron, very little oxygen manganese, calcium carbonate, chlorine, ammonia or even bacteria to some extent. The water temperature varies depend- ing on the depth of the water-containing stratum and the atmospheric temperature of the area. Generally speaking, the water temperature is 1 to 200 higher than the average atmos- pheric temperature of the area, and if the underground water layer is below 30 m, then the water temperature is about 1°C higher when the water layer is every 30 m lower. Therefore, it is necessary to expose the water'to the air and also to purify* it. (Fig. 29) Shallow Well: This type of mell is used when the underground water level is not too deeP, and the underground water is abundant. The area may be between 49.6 and 66.1 m2 , and the depth of the well could be about 3,5 m or less depending on the underground water vein. The surrounding is protected with either concrete or board, and set a well frame with 1 to 1.5 m of diameter at the centre of the well. The depth of this cylindrical well frame may vary depending on the level of the underground water, and between 6 and 10 m. Inside the well frame, a vertical pump is placed and the water is pumped out.

Translator's ote: In the saràe order as written in the original. Perhaps better be placed two sentences earlier. - - 155

(6) Construction of the Pond The land in which the eel pond is built is a paddy field, low productivity farmland, or unused salt field, and when the site is selected, the land is prepared for building a pond. First, position and level of the drain relative to the sea level must be decided. If the pond is very close to the sea, the level of the drain is determined taking the level most convenient to drain the pond as the zero level, and this level is of course determined only after taking the sea level at the high tide into consideration. The pond is built with

1/300 to 1/500 of the bottom slope, taking the position of the drain at one corner of a rectangular form. There is no need to consider the level of water inlet because the water used for the pond is almost always underground water nowadays. When the designing is completed and the pond shape is drawn on the ground, a dyke is built to surround the pond, using the surface soil of the pond. This preparation is especially easy as heavy construction machines are readily available these days. Construction expense is highest if concrete wall

is ui-- ed for the pond wall. To replace the concrete wall, this suthor hihly recommends the use of thin concrete plates,

(0.6 x 0.9 m) x (0.05 - 0.06 m) or (0.3 x 1.2 m) x 0.045 m.

nese concrete plates are placed side by side with 1.5 - 2.0 cm

intervals along the side of the dyke built with 1/300 - 1/500 . of slope and connected with cernent. Usually the concrete plate - 156-

does not have to be ferro-concrete, but if needed, 3 iron

bars vertically placed and 2 iron bars horizontally placed will reinforce the strength of the concrete plate. The (0.6 x

0.9 m) x (0.05 - 0.06 m) plate weighs 45 Kg and the 0.3 x 1.2 m) x 0.045 m weighs 43 Kg and the difference is only a slight amountl but the actual labor efficiency is greatly different. Two women and 3 men can make about 90 to 100 plates per day. If a concrete pond wall is to be made, pine stake and gravel

are needed for the foundation, and at least about 1/3 of the wall must be underground below the bottom of the pond, but if

the concrete plate method is applied, it is needed to dig /80 only about 5 to 10 cm below the lower end of the plates and

to place wood plates, 0.36 x 0.12 m, before placing the

. concrete -plates on top of .the pine wood-plates. -The pine wood plates are sufficient to take the weight of the plates, and yet they are quite durable in the water and inexpensive as

they are wood boards. Labor required to build a pond is . approximately 130 men (men 70%; women 30%) per 991.2 m 2 .

(Fie. 30) - 157 - • 8. DISEAiJE AD NATURAL ENEMY: THEIR PREVENTION AND REMOVAL 1) Ikari-Mushi (literally, Anchor-Worm) Since an anchor-worm was first discovered in an eel pond near Toyohashi, in mid-July, 1922, it caused serious damage to the eel culturing business in many areas. Methods of preventing the damage and removing the parasite have been well established since then, and the extent of damages is not at all serious. Nevertheless, the parasite is found quite frequently. (1) Morphology • As shown by its name, anchor-worm, its body shape resembles an an anchor. Its head ié a semi-sphere and protrudes out of the plane of the parasitic organs. The eye(s) is buried under the skin near and behind the top of the head, O The adult female is about 12 mm long from the top of the head to the end of the egg sack, and the axis of the body isusually arChed. There are parasitic organs around the head, and the 2nd and 3rd thoraxes are narrow like a neck, but the 4th and 5th thoraxes are thick, The 5th thorax and the front genital organ which lies on the abdomen at the end of the 5th thorax and the trunk are all joined together in a shape of a boot. The front end and the rear end of the third thorax are bent to either left or right of the longer axis in about a 900 angle. Therefore, if the body is placed on a flat plate on a supine posture, then its body below the 3rd thorax is bent to either . left or right . The body at the larval • st, -e is not bent. -158-

The parasitic organs are separated from the head by • a clearly distinguishable ring. One pair of the organs that protrude forwards and towards each side is simple but the other pair that protrude sidewise and towards the rear are thicker than the front pair, and about 1.5 times as long as the front pair. It also has a branch that sticks out in a right angle, on each side. The length of the branches are equal to or shorter than the length of the front pair. The parts of these parasitic organs have different shapes depending on the age of the parasite and on the parts of the fish that it attacks. • When it starts to attach to the host, the parasitic organs are only 4 protrusions on the 1st thorax, but as it grows, the organs become conicals of identical size. Later, however, the ones on the rear develop faster and branch out, - and finally assume the shape described in the above. This is to say, the parasitic organs develop and assume different physical shape corresponding to the site of attack and to the age. • (Fig. 31) The shapes of Darasitic o'rgans are not identical, however, and Some look like a harpoon when viewed from the side, and the shape of the branches also vary as sharp end, round end or stick. The larva undergoes a series of metamorDhoses, /82

nauplius, metanauplius and 1st to 5th copepodid, before it

becomes an adult e

(Fig. 32)

aUpiiUs F2 ,2rio3: " lien the ej;z hatches, it produces an oval - 159 -

shaped larva, with 0.15 mm of average length and 0.10 mm • width. The body length is approximately 1.5 times as long as the body width. It has no pigment and transparent but the digestive organ is pale green. The abdomen is flat but the back is slightly curved, and it has no eye. The first antenna consists of two segments, and not branched. The . lst segment is longer than the 2nd segment, and there are three spinules, 1st, 2nd and 3rd. The 2nd segment consists of endite and exite, and has a short bottom segment. The exite consists of 4 segments, the 1st segment being long and thick, the 2nd and 3rd thick and short, and the 4th . thin and long. Insidesof the 1st, 2nd and 3rd segments have one each of feather-like bristles, and the 4th segment has one well-developed feather- • like br4 stle -nd one sp 4 nule on each,side of it.. The mterior leg* is smaller than the 2nd antenna, but except that it lacks a terminal segment of the exite and a spinule on the endite, it is identical with the 2nd antenna. The larva has the statoleg at the rear end of the body. Metanauplius Period: The body does not have pigment, and it is a transparent, elongated oval. Its back is slightly curved but its abdomen is flat. Its average body length is 0.16 mM and body width 0.10 mm. At this stage, a compound eye(s) appears clearly at the front end of the median line. It also has the telsons**, and at the end of each telson, there are 3

* Translator's Note: This word may not be correct. The author uses a word to be literally translated as "uppr-jaw-lei;." ** Translator's Note: This word may not be correct. Literally, "tail-leaf". Incidentally, literal trans lation of endite is "inner-leaf" • and that of exite "outer-leaf". -160 - spinules. The innermost spinule is large and thick but the outer 2 spinules are short and situated closely together. There is one spinule also at each side of the base of the telson. On the 1st antenna, there are 4 or 5 spinules on its 2nd segment, and on the 2nd antenna, there are 1 feather-like bristle at the terminal end of the endite and 3 spinules. These are the points that the metanauplius larva is different from the nauplius larva. Although no change has developed on the anterior leg itself, a new cupola, a source of the 1st lower-jaw-leg, which carries 2 spinules, appears at the rear of the anterior leg. (Fig. 32) The First Copepodid Period: The body is pale yellow, and there,are,a.pair of .eompound eyes mear the f'ront end on the , back. The digestive organ contains a large number of dark /83 green granules, and therefOre, it can be distinguished quite easily. The body segments can be divided into 1 large cervical- " thoracic segment, 3 thoracic segments, and 1 abdominal segment. The telson is situated at the end of the abdominal segment. Its average body length is 0.47 mm (including the tail spine). The 1st and 2nd antennas are about the same length, both consisting of 2 segments and the 1st segment is about 1.5 times as long as the 2nd segment. The telsons which are situated at the end of the abdominal segment has one very long tail spine and 4 spinules on the outside of the spine on each telson. 2he 1.,rva also bas the 1st and 2nd swimming legs. it grows, the numbers of antennas and swimming legs and - 161-

also those of Ieather-like bristles and spinules increase. Major points of differences among the 2nd stage and later copepodids are listed in the following table. (Table 17) Life History: The larva has a strong heliotaxis property and moves around in the water quite actively, but when it reaches the stagesof nauplius or the 1st coPepodid, it starts to live a parasitic life. Unless it finds a host, it dies out.. The larva wriggles on the skin or inside the buccal cavity of a host eel, but stays away from the host for a short period from time to time and swims around in the water and comes back to the host. At the stage of the 5th Copepodid, it copulates. The male dies after a certain period, but the female extends • its body segments, and after this metamorphosis, it digs into the tissues of the host and remains to be parasitic. The female at this stage has a pair of egg saOks at the end of its tail, and holds about 200 eggs in one egg sack. When the time approaches close to the hatching of the eggs, the sacks break naturally. The eggs are produced in the female body twice* and seldom three times*. When the egg hatches late in the fall, the larvae pass the winter without formation of the egg sack. The anchor-worm does nOt form eggs in winter,

and neither the eÈ;îs nor the larva passes the winter. That is, only the female after the metamorphosis passes the winter.

• * mranslato -o's :Probably in one year.

- 162 -

There are two .types in the overwintering females; one is at the beginning stage of the metamorphosis, and its body is wrapped around in parasitic skin tissues forming a small bump of 3 to 4 mm diameter; and the other type is that the body of the worm is exposed and the size of this part is variable. The former can be detected quite easily and found more frequently than the latter with the exposed body, but unless it has already deeply perforated into the host tissue, it may fall off quite easily. If this occurs, then the swelling also cures by itself in .a short period. Therefore, the host eel is not seriously injured. On the other hand, the ones with the exposed body are difficult to be removed, and they grow quickly in the spring, form the egg sack and start out the /84 multiplication. The latter type is often found in the buccal 11› cavity of the eel. The temperature range suitable for multiplication of the anchor-worm is quite wide and it is between 14 and 32°C. The period required for the development of various stages during the season of multiplication and the Water temperature are listed in table 18. (fable 18) (2) Method' of Removal For the removal of the anchor-worm, in an eel pond, it is very imtortant to detzt the presence of anchor-worms ready to pierce the skin of eels in the tond or which already became a parasite to the eels,at the earliest possible date, - 163 -

and to remove the worm by methods unaffecting the host eels. It is usually too late to find the parasites, if the eels do not feed well. By then, the host eel is too weak and it does not have sufficient resistance power against the chemicals. Since the female worm after the metamorphosis (the worm already attached on the fish body) has much stronger resistance than the larva, it is perhaps best to try to prevent occurrence of further parasitic actions of the worm, and wait for the

. parasitic female to die out. It is important not to deteriorate the water quality. There are three methods currently applied for removal of the anchor-worm. 1) Use of Sea Water This method iQ nativr...1 1 ,y suitabJ..e on.l.y.n the area where sea water is readily available. It has advantage in that it is inexpensive and can be performed quite easily. The larva and egg of the anchor-worm can survive at 3 o/oo of salt concentration, but at 4 to 5 o/oo, it is quite strongly affected, and at 9 o/oo or higher, they are perished. It is important to note that, since it takes 6 days at 20°C of water temperature to completely destroy the anchor- worm larvae in 6 o/oo salt water, it is necessary to retain this salt concentration in an eel pond for at least 4 or 5 days.

However, this method does have serious disadvantages

that since it requires to maintain a fairly high salt concen- tration, its effects on a mixture of fresh water fish (carp - 164 -

fish, gray mullet, or loach) are quite serious, that the plankton phase of both zooplankton and phytoplankton changes rapidly and it takes quite a long period to restore the plankton phase to the original or ideal state, i.e., a rich vegetation of the "blue-powder", and that, during this period, /85 the conditions of water are quite unstable and consequently feeding cannot be done properly.

(Table 19)

2. Bleaching Powder Since bleaching powder is cheap and easy to handle, it has been used for the purpose since olden days.

(Fig. 33) The three day lethal concentration of its effective

-chIorine , against , eggs ,and larvae-of the-anchor-worm Is 1/4000,000

(weight ratio), but it is 1/150,000 to 1/300,000 against the /86 . eel and carp fish. Therefore, if the bleaching powder or chlorine water is evenly applied to the pond water to maintain

the effective chlorine concentration, 1/1,000,000, then the removal can be achieved effectively. When this method is applied, since the difference between the lethal concentration against the eel and the anchor-

worm larva is small, it is at,most important to calculate the water quantity of the pond very accurately so that the approp- riate concentration of the effective chlorine results accurately. Otherwise, the eels in the -..2)nd suffer quite seriously and the entire operation may end up in a coraplete. failure.

- 165-

Since the larva is heliotropic, it is most • effective to apply bleaching powder when the larvae gather on the water surface. 5. Dipterex This is a kind of commonly used agricultural chemical. Dipterex is effective against anchor-worm larvae, leaving only a part surviving at 0.1 ppm, but destroying all at 0.2 ppm in 2 days, 0.5 ppm in I day, and 1 ppm less than I day. The larvae at the copepodid stage parasitic to the fish also fall off and die at these concentrations, but the female,after the methamorphosis and attached to the fish with its hook, can survive for 5 days at 30 to 50 ppm, and its II› ,eggs.still_inside the egg sack may hatch at a 40% hatching rate after being treated for 1 day at 10 ppm. (Table 20) Resistance of the fish against dipterex is relatively strong, and the chemical is perfectly safe against the fish at 0.2 ppm. Its safety concentration against the fish is variable depending on the fish species but it is between 2.6 and 7.9 ppm. It has no maleffect on the feeding of the fish at a limiting concentration range between 0.2 and 0.5 PPm. When dipterex is applied to pond water at 0.2 to 0.3 ppm to destroy anchor-worms, some . zooplankters, particularly • Crust:.:Ïcea are destroyed completely, but other zooplankters, - 166 -

for example, Rotifera, are not at all affected,even in its multiplication,by the chemical. Oh the other hand, the chemical does not show any effect on the growth and multiplica- tion of the phytoplankton at 10 or 50 ppm. Therefore, if this chemical is used, there occurs no unfavorable side effects such as changing-water or loss of appetite of eels which does occur when sea water or bleach- ing powder is used to destroy the anchor-worm. On the contrary, /87 the after-effect of this chemical is a good one that the eels show better appetite. (Table 21) The best timing for the use of dipterex is early in the spring but not too early when the overwintered females -still-hold eggs in tbeir egg sacks,, because the ,chemical-at 0,2 ppm kills neither the females hooked on the host nor the eggs in the egg sacks. March is when the parasitic females start to incUbate eggs in the egg sacks and the larvae produced when these eggs hatch are the 1st generation of the year. (3) Preventive Method The route of propagation or introduction of the larvae into the eel pond is naturally through the water taken into the pond from outside. As the water for the eel pond is mainly underground water in recent years, this route of ropapAtioh is not seriously important to take into considera- tion, ?ho other route is troull the female which completed • the r:itamorphosis. To prevcnt this route of propagation, the - 167 -

culture stock should be examined carefully when purchased to • see if the fry carry any parasite. If the parasites are found, they must be removed with either chemicals or sea _water. It is desirable to apply the dipterex method in spring when the temperature reaches 14°C regardless of the presence or absence of the parasite. 2) Hire-Aka Disease (literally, fin-red disease) This disease is a typical infectious disease, occurring quite frequently both in Europe and in Japan, and it causes quite serious damage to the eel fishing and eel culturing. One serious case of this disease was reported in Italy in 1718. It usually occurs in spring and summer but occasionally in fall and winter. The epidemic starts slowly in most of the cases but sometimes very suddenly and violently. When the epidemic spreading is quite extensive, a large quantity of eel may die suddenly but usually the infected eels die slowly one by one, and the dead eel may be hidden in the "blue-powder", delaying detection of the disease. The diseased fish is so weakened that a large quantity of eel may fall dead during subsequent pounding, transportation or at the time of freshening the eel pond. Shirasu-unagi may not be found to be infected often, but the eels with 100 to 200 g of bodàr weijnt are the ones that most frequently suffer from bhe disease. • (1) Causative ncrobes rnere are two kinds of causative organisms, - 168 - • Aeromonas punctata and Paracolobacterum anEuillimortiferum, and occasionally mixed infection of the two organism occurs. Aeromonas punctata: It is usually found in water or in floating mud. Its shape is a small bacilliform, about 0.9 x 2.0 4 x 0.6 - 0.9 4, round at both ends, and has a piece of polar thread-like :hair. Its flagellum is thin and is about 2 to 3 times as long as the length of the bacilliform. The optimal temperature for the growth is 28 °C, the optimal pH between 7.2 and 7.4, and it contains à toxine. The toxine deactivate functionings of heart and intestine but not seriously. Paracolobacterum anEuillimortiferum: This is also a bacillus and its ends are round. It is 2 - 3 11 x 1 11 large, has a • piece of long 'hair and 15 -flagella, and it •moves -around quite actively. The optimal temperature is 30.8 °C when pH is between 5.0 and 10.8, and the optimal pH is 7.2. It also has a toxine, and not only the eel but also the carp fish, gold fish, rainbow and frog are fatally infected.by the organism. (Fig. 34) (2) Symptoms and Pathology The disease is injurious ina.d.nly to the intestines, liver, and or kidneys, and when the fish is infected by the organisms, its fins and skin become red, and occasionally tumor-like swelling occurs on the body surface. The route of infection i ininly oral but occasionally cutaneous. Since !I> iie skin of Lhe eel is always wet with its mucus, no.healthy - 169-

skin or gill could be infected but when the skin is injured by the anchor-worm or mechanically by'rubbing against stones or pond walls, the infection could occur. At the initial stage of the disease, the anus becomes enlarged and reddish. The red color also develops on the fins and on the skin, due to the congestion of the blood vessels near the skin but there occurs no change in the muscle tissues under the skin. Inside the abdomen, the disease symptom is most serious in the intestines. There is a considerably advanced blood congestion, and at the advanced stage, the tissues are loosened, and the inside of the wall is inflamed containing mucous liquid. The liver is also highly congested, and it is particularly serious in the rear Thespla.cn.ds_usually swo1len, .?,nd.so is the kidne,y. Occasionally, there is an ulcer in the liver and kidney. No visible disease symptom is found in the gills and in the heart. The diseased fish feeds auite poorly, and although its appearance is not different from the healthy one, it moves around wildly at times. It usually, however, stays afloat on the pond surface or near the water inlet, often bending its body in an arch as if it is completely exhausted. When the disease grows worse, the skin color fades and the heart functions start to fail, and it dies eventually. Some do, however, recover luckily.

The course of the disease varies. If the disease • is an acute one, it takes only sevei?al daY-s to kill an eel - 170 -

after it is infected. The incubation period is usually 2 to • 3 days in summer and 1 to 2 weeks or longer in winter. When the disease progresses slowly, the eel becomes anemic quite seriously. If an eel is infected with the organism once, and then regains the strength after the disease,.the eel which has recovered appears to have aquired an immunity against reinfection. (3) Prevention and Cure • The first important thing is to avoid transferring a diseased eel into an eel pond.' The causative organisms cause the disease of not only the eel but also the carp fish and other fresh water fish. • If -an-eel -which .does not feed well , or •tays calm nearly vertically with the head towards the side of the wall or the water surface, it should be caught and served as food, as it is harmless to human beings, burned or buried in the ground. Since the diseased eel does not have a good appearance, its commercial value lowers, and the one which has suffered from the disease chronically does not have a good taste, because it is anemic. Nevertheless, it is quite safe to eat the diseased fish. Since the diseased fish hold the infectious microbes, it should never be discarded in any Water It is important to disinfect e el ponds at least once a year and, of course, whenever some degree of damage - 171 - was caused by this disease. The method of treatment has not been established too well, but if the diseased fish is placed in cold, fresh, running water, the fish appears to regain the strength and recovers eventually, only if the disease is detected promptly, and treated as soon as possible. As a chemotherapeutic method, antimicrobial drugs may be added to the water or mix with the feed and administer to the diseased eel. The latter is an effectiv e . method, but if the eel does not feed well, it cannot be applied. Among the effective antibiotics, chloro- mycetine appears to be the best of all, and penicillin is the least effective. Among the sulfur drugs, thiazine is most effective. When sulfur drugs are administered by injection*, the progress of the disease can be checked if the injection is done at the beginning stage of the disease. Dose of the injection is about 7 mg per day per 100 g of body weight. Oral administration of thiazine, 100 to 150 mg per day per 100 g of body weight, for several days, is quite successful in curing acute infection of the eel with this organism. 3) Mizu-Kabi Disease (literally, water-fungal disease)** /90 (also called ',8,ta-kaburi disease ((literally, cotton-covered disease))** or sure ((literally, abraision))**) Since olden days, there has been a disease known to be caused by an aquatic funGus, and the traders in the eel

* Translator's rote: Undoubtedly intramuscularly, but the author does not specify. ** TranslatOr's Note: Added by the translator.

,7,--.M,ç7.5'rePeM±77M,,,r.met - 172 -

culture call the disease wata-kaburi or sure. In recent years, • the disease occurs in spring when feeding starts, and a great deal of damage is done every year. (1) Symptoms The causative fungus grows near the front end of the head, tail or on the main body, as if it covers these parts with cotton. Furthermore, floating mud or vegetable plankters attach to the well developed, cotton-like hypha in a large quantity. The diseased eels swim near the water surface with little strength in miserably dirty appearance. They usually die within a few days but some survive and recover when the fungus falls off the site of the parasitic - growth. When the eels are infected by the fungus, they do not come around to the feeding post, and do not eat. There- • fore*, it appears that there is a latent period in thib disease. • The disease occurs mainly in late March to early May, and it is particularly prevalent when the water tempera- ture is somewhat unstabilized at 1500 and the weather condi- tions vary frequently. The epidemic spreads and lasts for a milther short period, but Gives serious damage to the business. It also occurs when the temperature lowers in the fall, and almost always after the ponds are freshened up late in the fall. When the water temperature is raised above 20 °C, the disease also disappears.

41› , Translator's rote: The reasoning is not too clear>to this translator. - 173 -

At the site of the aquatic-fungal growth, the skin • is almost decomposed, and when it falls off together with the aquatic-fungal, badly congested muscles appear. The aquatic fungus penetrate a part of its hyphae through the epidermis, dermis and, at times, the muscles, and covers the parasitic part of the fish with the hyphae, and gradually destroy the tissues at the site. As a result, it is not rare to see the jaw bones naked. The eyes often become white and turbid, the diseased eels nearly becoming sightless. Some eels suffer from the infection inside the mouth, and others show nearly identical symptoms as those of the fin-red disease (previously described), their tails, tail ends of the fin,, or anal regions becoming red. The latter symptoms may indicate secondary 110 -infection lpy microbes.. Ehirasueals_suffer_from this_fungal infection quite often, and die easily. (Fig. 35) (2) Pathogenic Fungus The parasitic fungus is . an aquatic fungus Sa -orolegnia parasitica Caker, and the disease is caused by the monotypic fungal parasitism of this fungus. The fungus is widely /91 distributed throughout the fresh water basins in this country, and not only eels but also many kinds of fresh water fish and their eg!:7s suffer from its .infection. Its hyphae develop very well, the major hypha having aoout 20 of the diameter and the branched hyphae, between 10

and 20 la. Its zoosporangium has a bacilliform, 15 - 45 11 X 50 -

4J0 p. , and the secohdary zoosporangium is kidney-shaped with - 174 -

about the same size as that of the primary zoosporangium, and • after a period of dormancy, if the environmental conditions become suitable, then it converts itself to the vegetative hypha. In addition to the formation of the zoosporangium, it often forms a gemma, which is any of the various forms such as oval, global, bacilliform, streptococciform and various other forms. It either forms a zoospore or extends a hypha. The oogonium is either terminal or intersex and the former is usually global, about 58 - 86 4 x 49 - 60 4. Number of the zoospores also varies from 3 or 4, a little more than 10 or many more than 10. The zoospore . is global and its diameter is between 20 and 30 4. It germinates on an agar flat culture medium at room temperature within 48 hours, becoming a mycelium vinile tn the nn.ked r>y°, .Sonie of the antheridia are homolegous and oth\. rs\ are not. Both types of antheridium, however, are not found \ in spring and fall when the fungus is parasitic to the eel. This fungus does not appear to contain any toxine. (3) Removal No reliable removal method has been established as yet, but the malachite green method appears to be most effective. Its concentration to inhibit the elongation of the hypha, formation of the organs and other similar growth 7related functions of the fungus are about 0.1 ppm. The mycelium is

sterilized at 0.2 ppm in about 180 to .220 minutes, and the • sre killed in 50 minutes at 2.5 >,Dpm and in 70 minutes at - 175 -

The concentration of a malachite green solution in • which the eel can survive for a prolonged period is about 0.07 ppm for shirasu-unagi, and 0.125 ppm for the'eel more than 1 g of body weight. For short period bathing in the chemical solution, the concentration can be raised to 3.33 ppm for 1 hour against a shirasu-unagi, and 3.33 ppm for 2 hours against the eel with more than 1 g of body Weight. Therefore, for the removal of the aquatic-fungus from the eel weighing over 1 g, the chemical should be sprayed into the culture pond at 0.2 ppm, and the shirasu-unagi should be treated with a 3.33 ppm solution for half an hour or an hour. In order to prevent the disease, it is important to carry out this disinfection of the culture stock with a malachite gree solution before releasing the juvenile eel into a culture pond. It is also important to clean and disinfect the pond bottom when the pond is refreshed annually, and it is desirable to sterilize the pond water as well, early in the spring. 4) Ki-Ho Disease (Pir-Bubble Disease) The shirasu-unaf_;i is the victim of this disease, and the eel over 6 cm of body length does not suffer. A large number of air bubble lumps appear on the skin particularly

on tri head, and i„,:as- builds up in the subcutaneous connective tissues. • (Fig. 36) /92

• - 176 -

The sick fish swim near the water surface because of the buoyancy created by the air bubble. When left aside, many of the victims die out but some heal gradually. Two causes can be considered for the disease. One is the excess oxygen in the water. When the water temperature rises, green algae, Myxuhsyceae, and other phytoplankters grow rapidly, and the oxygen content in the water becomes quite high. When this is the cause, the bubble bump is extremely large and when left as it is, it may puncture explosively. As a curative method, the victim fish may be placed in calm cold water with low oxygen content. The other cause is due to the presence of excess nitrogen, and if the degree of saturation of nitrogen gas rehps un%, thPn P.11 the PelP in the pond mn,y hP destroyPd: When this supersaturation of nitrogen occurs at low temperature, the air bubbles are very sffiall and a large number of them are proàuced but at high water temperature, a small number of large size bumps occur. The gas inside the bump is mainly nitrogen. Since the bubbles are found in .the muscle tissues as well as in the blood vessels, the direct cause of the death of the diseased fish appears to be the blocking of the blood circulation. This disease has quite a high incidence rate when underground water is used. 2or this reason, if nitroï:;en

content in the underground water is hiEh l the water must be exood to the air before use. - 177 -

5) Cutaneous Parasitic Disease As parasites on the skin of the eel, the following 4 species in 2 genera can be cited. All these become parasitic on any part of the skin and cause skin diseases. They are p:yxidium anpuillae, LentosDore dermatobia, Mmidium matsuii, L. anuuillae. and At the beginning of the parasitic activity of these parasites, milk-white, very small circular dots appear on the skin. As the parasites multiply, the circular dots become larger and larger like a cloud of smoke, and the skin breaks down and decomposes. During the.course of the disease, the infected eel excretes a large quantity of mucus, and it feeds poorly, and finally dies in exhaustion. Morphological and ecological characteristics of the parasites are presented in table 22. For the treatment of this disease, the malachite green bathing and dipterex spraying are commonly applied. 6) Muscular Abscess This disease spread in Aichi- and . Shizuoka-prefec- tures in 1933 to 1935. The shirasu-eel is the victim of this disease most of the time, but in 1931 and 1932, adult eels, longer than 30 cm, suffered from the disease. Since 1937, no case of the disease lias been reported. (Table 22) (1) .;ymptoms Victimized shirasu-eels loose weii-;ht and become • like a thread, and their spinal bones can be seen throuGh

Mrrr-77'1",7'.77,'7 - 178 -

the skin. The body color changes to black but at parts, • the color fades out. Adult eels do not loose the weight as much as the younger ones. The skin does not show particular change but its body side muscles are dent in concave and abscesses occur. The victimized eels still feed at the initial stage of the infection, but they gradually loose weight and swim near the pond surface in a vertically suspended posture. The disease occurs abruptly within a short period and it is quite highly epidemic. (2) Pathogenic Parasites Plistophora ancruillarum is the major pathogenic parasite of this disease. Mmxidim sp., Myxabolus sp. and others are also known to cause the disease symptoms. The • kinds of parasite and their appearance frequencies are shown in the following table. (Table 23) /94 The kidney is the most common pathogenic organ - attacked by the parasites. The most frequentiy appearing • parasite is Myxidium sp. in this organ. The parasite in the muscles is usually Plistophora anruillarum. These two species appear to be the major pathoenic parasites and the abscess of the muscles is caused almost always by Plistnhora sp. Other organs are attacked by a mixture of various parasites. Plistoohora an,;zuillarum has a sporont which forms more than 16 spores. When the sporont is built in the muscular • fibre, it becomes several sporoblast, forriing spores. The

O - 179 -

sporont disappears when the spores become mature and expelled • into the tissues. No particular siporangium formation is observed. The sporont is global and about 12 - 41 g large

and the sporoblast has 10 to 13 g diameter, containing

spores between 4 and 8. The spores are oval but have a curve

towards one side. Their major axis is 8.5 g and minor axis

4.6 g and its large portion is a vaduole, 5.4 g. of major

axis and 3.8 g of minor axis, but the polocyte is not very

clear. The pole thread is extremely long, about 430 g and

when fresh, it has 3 or 4 horizontal lines on the vacuole.

(Fig. 37)

nxidium sp. is parasitic mainly in the kidney, and causes extensive damage to the function of the organ. This parasite does not form a skin sack* of spores when it • becomes parasitic in the tissues. The parasite is widely diffused in the organ. The spores are somewhat round and

spindle-shaped. It has 8 vertical stripes on the outside

membrane, and a suture is seen at the centre. The size of /95 •

the spore is 8.7 x 5.4 g and its cross section is almost

circular. The polocytes, 3.1 x 2.9 g, are round and situate on noth terminal ends of the spores. The polar thread has not been observed. The kidney, is particularly vulnerable to many kinds of parasites. ( : ) Re:noval Sire the life .istory and spreading route of thee parasites are not very well 'mown, the - ethod of removal

* Translator's Note: Literally translated. Sporangium? - 180-

of the parasites and prevention of this disease have not been • established. Before placing shirasu-eels into an eel pond, microscopical examination of the kidney and muscles should be done. If diseased eels are found to carry the parasites, they should not be released into ponds. If the diseased fish are found in a pond, they should be captured, and either be burned or buried. Since the diseased young eel does not grow, it should be destroyed as soon as found without lingering attach- ment. 7) Kidney-Swelling Disease or Fat Hip Disease The outlook of the diseased fish is very much like that of the ovarian cyst. The diseased fish have swollen abdomens and they are either incapable of swimming or behave abnormally. The kidney is swollen and yellowish white spots are detected. There is a Pale yellow, stiff .gelatinous mass . of irregular shaped kidney. The gelatinous mass has a cavity inside and turbid yellow liquid fills the cavity. The disease is caused by unbalanced diet, and when aGed feed, containing too much fat or oxidized fat is given for a long period, the disease may occur more frequently. S) Dispase of Digestive Organs Presently, the following parasites are known in the di g estive organs, and degree of damages directly caused by the parasites or symptoms are not too well known. In the stomach, 3 spcies of 3 genera of Trematoda • end 1 of 1 '-.;enus are known, They are - 181 -

Tubulovesicula anEuillae l Seterrhurus musculus, Heliconema anEllillae and AzyEia anguillae. In the intestines, 1 species of 1 genus of Cestoda, that is, Bathriocephalus laEmicus and 1 species of 1 Genus of AcanthoceEhali, that is Acanthocenhalus Eotoi are known. 9) Skeleton Disease The skeletal curvature is the major disease in this category. This disease is represented by a meandering spinal bone and it is, therefore, a kind of deformity. The disease occurs mainly in eels under artificial cultivation, with body lengths longer than 25 cm. It has not been found in younger eels or in natural eels. The disease is caused by malnutrition, especially when silkworm pupae are given to the culture eel as the only • feed, but the eels feeding on fresh fish do not develop the disease. It is due to the Aeficiency of minerals and vitamins. 10). Other Diseases In the category of diseases of respiratory organs, Protozoa and Sporozoa which are parasitic on the gills, destroy the gill tissues and the victimized eels may die from exhaustion. In the category of blood vessel diseases, HastiEEEhora of Protozoa is known to be parasitic in the blood /96 vessels. The most popular ones are Truanosoma sp. and rarely

A2amoncna sp. In the air bladder, there are several kinds of parasites known but about 805 of them belong to Nematoda, and the bladder wall becomes very thick at times. The representa- • tive species are Anguillicola globicens. In the eyes, - 182 -

Philometra anguillae of Trematoda makes them turbid and the vision is impaired, but the eye balls do not stick out. In 11› the genital organs, ovarian cyst has been reported in foreign countries. In this country, cases of degenerated genital glands have been reported, but this type of disease is not at all important in the aspect of productivity in the eel industry. 11) Vermin (1) Species Since the eel culture ponds are usually situated near the coast, there are numerous species of vermin coming to attack the eels in ponds, and in large numbers at times. For the fish culturing, the extent of damage caused by these injurious birds is quite serious. Since most of the • naturally and artificially caused damages to the fish culture are, to a certain extent, expected and perhaps even controlable, but the birds fly towards the eel ponds at unpredictable times and frequencies, and feed on the eels under cultivation. The extent of the loss of healthy, growing eels is difficult to estimate in most of the cases, and therefore, it is often overlooked, or the fishermen in this business are resigned to the loss. The kinds of vermin that fly around the eel culture ponds in Yoshida area of Shizuoka-prefecture consist of 9 families and 16 species, and they are mainly migrants and

oirds 01 passa„;e0 - 183-

The following birds are the ones most frequently appearing in the eel ponds. Koajisashi or Chunai: Every year,late in April, they fly in and lay eggs on sandy shores along the river Oigawa between June and August, and in late August, the juvenile birds fly towards the eel ponds with their parents. They fly south late in September and early in October. The number of eggs laid is 2 or 3 at a time. The birds are quite popular in many countries in the south. A large number of the birds attack the eel pond incessantly in the season, from dawn to sunset, and feed mainly on juvenile eels. The bird is quite voracious, eating 10 small eels 5 or 6 cm long, and 12 small carp fishes 3 or 4 cm long. The bird is not frightened away by a gun report, and easily habituates to the wires or colored ropes stretchéd over the ponds. Sea-gull or Charo: This is a winter bird that flies to the eel «ponds from the middle of December to the beginning of May. When the fish haul in the sea is poor, large flocks of the birds attack the eel ponds. They fly around the eel ponds from dawn to sunset, particularly early in the morning or close to sunset. :::hen the culture stock is released into a pond, the juvenile eels tend to stay on the upper surface of the pond water; when the pond is being freshened up, the water depth becoes shallow, anu the eels can be seen easily; when the pond water becomes transparent due to the chaning-:water during winter, the eels can be seen easily; and when the water tempera- • Lur'e rise, the eels cime towards the water ;:iurf,,tce. These - 184 -

are the times when the eels are caught by this bird. • It eats between 7 and 30 juvenile eels within 10 minutes, and therefore, the loss of the culture stock is quite serious. The eels caught and eaten are usually smaller than 25 cm body length. Large sized, healthy eels may be caught once, but it slips out of the bird's beaks, but sick eels or slow moving eels become the victims. Anguillicola Elobiceps which inhabits /97 the eel's air bladder and Heliconema anguillicola which is found in the eel's stomach, are carried by this bird. Night Heron* or Heron: This bird attacks the ponds throughout the year but more frequently in pring and fall. It attacks the eel pond only during the night, particularly before dawn. The bird catches eels by walking through the pond, and also • -standingon the,dyke, Therefore l dt is dmportant ,to be particularly careful when the water level is low during the refreshing of the pond. The bird is voracious and eats a large-sized eel (about 40 cm). Siberian Black Kite: It attacks the eel pond throughout the year, It always attacks the pond which contains diseased eels, suffering from the anchor-worm disease and others, or eels doing "hana-age". In fact, when the kite attacks an eel pond, there are almost certainly weakened eels in the pond. In addition to the above-described, a kashiwa (brown fowl) or Omizunagi-bird, kaitsuburi (dip-dapper or

little J.I.ebe) or ittyo-mouri, akaeri-kaitsuburi (red-colored

O

* Translator's Note: Probably Uzcticorax nrticorax - 185-

kaitsuburi), kawasemi (halcyon) or hisui, suzukamo (soaup duck), • kawa-aisa (goosander), hidorigamo (bald pate), umiu, himeu and others are also the vermin of the eel culturing. (2) Protection The methods of protecting the eel pond from the loss of the eels by the vermin are 1) to shield the eels from the vermin, 2) to set up intimidatory measures, facilities or methods, 3) to capture the vermin and 4) to interfere with the approach of the vermin to the ponds. It is quite useful to set up mylon cords or metal wires across and above the ponds to protect the ponds from à Siberian black kite, koajisashi, or sea-gull, which attacks the pond from the sky above the ponds. This method is in the categories 3)and 4) of the afore- listed.methods o It is important to : have,a_sufficlent.spacing between the water surface and the protective device so that the birds do not fly into the pond . It is also useful to space out the cords or metal linings and attach colored pieces of cloth, white or red, or bird's feathers to enforce the intimidatory effects. By doing this, the cost of the facilities can be lowered. When the changing-water took place, the method 1) is quite effective. If a piece of straw-mat or board is placed on the pond surface, the eels gather under the floating object and therefore, it is also a very useful method. - 186 -

9, CULTIVATION P:THOD AKD MAINTENANCE OF THE Porp 411 1) History of Cultivation of the Shirasu-Eel and Process of the Technical Development Presently, it is the only way of obtaining a culture stock to catch the shirasu-eel at a river mouth when it starts to ascend a river after the juvenile eel get close to the shore and undergo the metamorphosis, because the &Pawn- ing ground of the eel is in the ocean and artificial insemina- tion and hatching of the eel eggs cannot be done in industrial scales. Since the eel culturing business was initiated by Mr. K. Hattori in 1879, it expanded quite rapidly during the Taisho era (between 1912 and 1926), and already in 1917 and 1918, production of the eel culture stock was initiated. In the years 1919 and 1920, young eels (weighing 15 to 201E) as the culture stock were in serious shortage. In those days, however, the shirasu-eel was used not only as the culture stock of the eel culturing business but also for the stock to be released in the nature to the rivers and lakes in Toyama- /98 and Niigata-prefecture. As they had been caught and used in such a lare scale, shortage of the culture stock became even more serious in those days, and as a result, the price became quite high in 1924 and 1925, and indeed its price was higher

than bhab of the marketable adulb cultured eel in 1927. _it:ere was one detrimental .fctor involved in promoting the binese of r:Disin the eel culture .stock. That is, there had ben qune a erieue diEqput.? and deb,5te between two perons, - 187 -

Mr. Tokuhisa and Mr. Maruyama, the former proposing the rapid growth of the shirasd-eel and the latter the sluggish rate of growth, late in the Meiji era and early in the Taisho era (between 1905 and 1915). One fish farmer in Ishiki-village, Banto-county Of Aichi-prefecture, however, did start to 2 culture the shirasu-eel in a fish pond of 231 m 1 in 1918. Although this man's attempt failed, his efforts stimulated other fishermen's interest and spirit of speculation. In 1920, to meet the demand of the traders in the eel culturing business, a research institute of fresh water fish multiplica- tion was established in Aichi-prefecture (this was later transferred to Toyohashi Fish Culturing Station of FiSheries Training College of the Department of Agriculture and Commerce), • .and research.and developmental activities in raising the shirasu-eel as well as culturing the eel were set in the right direction. In 1923, Tanaka Fish Culturing Co. of Shimosawaki l was successful Otsu-village, Hoi-county of Aichi-prefecture in industrially raising the shirasu-eel following the method developed by the Aichi-prefectural Research Institute of Fresh Water Fish Multiplication, afore-cited. Later, an Eel Culturing Co. of Shimomura, izumi-village of Atsumi-county, Aichi-prefec- ture also was successful in industrialization of the shirasu- culture. From this time on, fisheries stations of various prefectures started their own projects of producing the eel culture stock. In 1927 and 1923, Toyohàshi Fish Culturin„; Station • of the Depart;:aeLt of Ai„;riculure and Co=erce was successful in - 188 -

a large scale industrialization of raising the eel culture stock, under the sponsorship of the Parliamental Recommendation of Establishing Eel Culture Stock Business, approved in 1925. The impact of the success was so serious that a group of traders in the eel culturing business in Aichi and Shizuoka prefectures planned and proposed a National Stock Rearing Station with a production' capacity of 187 tons near the lake Hamanako, in 1930. The need of such a centralized stock raising station was strongly felt by everyone in the business because the supply of the eel stock was especially short in 1929 and 1930. In Shizuoka-prefecture, the prefectural government started to carry out the feeding experiment of the shirasu- eel in cooperation with Fukuda Town Fish Culture Station of Fukuda-town Iwata-county of Shizuoka-prefecture, in 1930. The same experimental work was initiated by Yaizu Fisheries College of Shizuoka-prefecture, and both were successful in obtaining excellent results. In 1934, Hamanako Branch Station of Shizuoka-Prefectural Fisheries EXperimental Station was established near Lake Hamanako, and testings of shirasu culturing were carried out in a very large scale, and even- tually a standard method and condition of raising the required stock of the eel culturing buSiness was established. Although a private businessman's oriinal intention was only to raise the required amount of culture stock for his own use, but later the eel culturinu: business diversified, and raising the eel ou] bure etook sPn , sted itself from the main stream, and - 189 -

became an independent business. In these research and developmental eras, the eel culturing business, near the Lake Hamanako,enjoyed the best prosperity of all the areas where bhe eel culturing was popular. In recent years, use of the foreign shirasu-eel as a stock of the eel culturing,has been considered, and the traders in this business are taking very serious interest in it. It is hoped that especially suitable juvenile eels to the domestic eel culturing business are found from all the eel species in the world in the very near future. 2) . Production of Shirasu-Eel (1) Culture Pond The culture pond to produce the shirasu-eel is usually-built very simply, and the pond-wall is rarely built with a concrete wall. The pond shape is usually rectangular, and the depth is between 30 and 60 cm. The more simple ones are built by raising a dyke or pond wall on the flat land to hold a sufficient quantity of water. In such a pond, however, it is necessary to attach a board around the dyke to prevent the /99 juvenile eel escaping or jumping from the water. If the rain falls along the side of the pond wall, special attention has to be paid in preventing shirasu-eels from climbing the wall. The pond bottom may be built with mud containing 1;-)rce gunntity of sand, bu -'J the one with a 5mal1er pronor- Li_on of ne snd may be more useful, because althouL;h it does • create certain inconveniences in hauling the shirasu-eels, - 190 -

but it protects the eels from the cold by shielding the eels 110 in the mild and also it is useful when there is a flood, as the eels may more easily smuggle themselves into the bottom than into the sandy bottom, and thus preventing the eels from escapinG at a very heavy rainfall. The size of ponds vary depending on various factors, but a main pond is usually between 1 and 3.33 arès and a branch pond is . between 10 and 15 ares, some being 30 to 50 ares. The wall of the branch pond is usually built with a concrete wall. The total area of the branch ponds must be about 20 times as large as that of the main pond, and it is desirable to split the branch pond in 3 or 4 smaller ponds. As the pond water, underground water is ideal because of its warm temperature. It is poured into the pond by way of a water pipe, and no particular specification and designing of the water inlet are required. The water outlet is built with a concrete wall in the branch pond, but in the main pond, no particular draining facility is reqUired, except perhaps separating a part of the pond with a hurdle. It is

• lso useful to apply vertical pumping through a wire busket for draining water. The feeding statiOn-is darkened by using boards

in an area .of about 6.6 m 2 , and place a lump (60 watt). The size of the feeding post may vary depending on the size of the main pond. Disinfection of Pond: The pond must be thoroughly disinfected before the - 191 - juvenile eels are released. About 1 straw-bag* of lime per 1 are of the pond is sprayed thinly and evenly on the pond bottom, and exposed to the air. Before doing this, malachite green or dipterex is applied for the sterilization. (2) Release It is desirable to release the shirasu-eels captured in rivers as soon as they arrive in the main pond. However, if it is necessary to wait overnight for corne reason, they are left in a bamboo basket with cotton linings and dropping a small quantity of eels over the cover basket. However, if the temperature is below 5 or 6°C, it must be kept in a warmer place. It is quite dangerous to hold a large amount of the shirasu-eels in a small container filled with mater. .This type of pound is ,dangerous bzzause.it tends to suffocate the shirasu-eels. It is also important not to injure the skin surface when the shirasu-eels are handled, as these skin injuries often lead to more serious infectious diseases. Timing of the Release: The shirasu-eel starts ascending rivers late in October and from this season on to December, there are ample opportunities of capturing a large quantity of the ascendibg shirasu-el. Accordingly, the timing of releasing shirasu-eel into a main pond takes place between November and early in April. The exact time of day is not important !et-ber it i5 mornin or niu,ht, but the major factor determining

* Translator's i;ote: This unit is primarily for grains and 60 Kg or 132 lbs. - 19 2-

the timing in a day is the water temperature at its peak during the day of release. Amount of Release: Although there has not been any clear-cut standard as to the ideal quantity of the release, if the shirasu- eels released to a main pond feed sluggishly, then the quantity of release could be larger, and if the shirasu-eels start to feed quite actively, because of rising temperatures, the quantity of release should be reduced. It is perhaps reason- • /100 2 able to set a standard at 750 g to 1.2 or 1.5 Kg per 3,3 m of the pond area. If a main pond is uséd as a culture pond, one and the same pond may be used for the pond to which the natural shirasu-eeI is released from time to time within a long span -of time. Therefore, it is-desirable to -either .build -a few, 2 or 3, main ponds or to divide the pond into a few sections, and place the shirasu eel caught at the beginning, at the peak period and towards the end of the ascending period, separately. In principle, it is desirable to grade the shirasu- eels in a main pond in an early stage so that.the production of large-sized culture stock can be effected sooner. (2) Training for Feeding When the water teniperature rises to 10 or 1500, the shirasu eels start to seek food. Since they do not feed if the water temperature is below 10oC, it is quite unimportant to force them to feed. Accordinc71y, to meet the desired conditions of raisin the culture stock, that is, catching the - 193 -

shirasu-eel earlier and train it to feed earlier, the use of underground water with temperature higher than 15 °C is preferable. Use of - vinyl-covered pond or utilization of hot or warm spring water is a problem to be studied and improved in the future, as these improvements would certainly result in earlier feeding and earlier availability of the culture stock. The first step of the feeding is to train the shirasu-eels to a dim light at the feeding post between sunset and about 9 PM. When the shirasu-eels gather to the feeding post, a prepared feed,usually an ito-mimizu (thread-like earthworm*), mud-snail, small crab in a stream, corbicula (Corbicura atrata**), and short-necked clam, individually or as a mixture of two or more, mashed and made into minced flesh ball, is placed on a shallow wood box and placed_just below the water surface. Some shirasu-eels would start feeding right away while others. do not.. Within 2 weeks, however, about 70 to 80% of the released eels start feeding. After this period, a minced fish meat is used, gradually replacing the afore-described training feed. The fish used at this stage is sardine, mackerel, horse mackerel, lockington and others. The fish must be fresh and bones are removed first and the meat is passed through a meat grinder (1.5 mm mesh riate -oassed 4 tinas). The ratio of this minced meat to the training feed should be gradually increased and also the tiiinL, ; of feeding will be made earlier.day by day. • The amount of feed to be given to the shirasu-eel released should be about 12 to 15 of the body weight of the - 19 4 -

shirasu-eel to be fed, per day. This.amount is divided into a few portions and fed à few times a day. (4) Graded Cultivation In order to raise the productivity of the eel culturing business, it is important to grade the small eels from time to time, and feed the different grades of eels separately, and also to reduce the density of accommodation in an eel pond. In about 30 days to 50 days after the shirasu- eels are successfully trained for feeding, a remarkable difference in the individual body size starts to show among the shirasu-eels in the -pond. This is the time when grading and separate feeding is needed. • When the days of feeaing elP.pse ; the aifference in individual body size becomes even more pronounced, and this is a natural course observèd in any cultivation of the fish. It is, therefore, a challenging problem to artificially adjust and regulate the growth of the small fish. Before carrying out this graded feeding, the quantity of small eels of a certain grade to be released in -a new branch pond, must be determined based on the size of a pond and on the expected yield of production. It is desirable to make the new release quantity as small as possible, because once /101 the shirasu-eels are trained for feeding, their growth is particularly remarkable if the density of the released quantity is smaller, It is also desirable to release a u'oup of stock - 195 -

eels with a smallest possible degreè of variation of the body size (degree of the lack of similarity of the body size). That is, the body size of the stock eels to be released in a pond should be as even as possible. A group of stock eels with a larger degree of variation in body size shows a poorer body wéight increase rate against the feed than a group with a smaller degree of variation, and also the former group shows a large ratio of the loss. (Fig. 38) Namely, when the degree of body size variation is large in one group, larger fish in the group eat far more than the smaller fish by driving the smaller fish away from the feed, and the former also eat more frequently than the latter. Therefore, even though the smaller fish are expected to increase their body weight faster at any time during their growing period to a certain adult size than the larger fish, if it lives with the larger fish, its actual rate of growth is much smaller than that of the larger one. In other words, if the smaller fish have to feed on a fixed quantity of food in competition with the larger fish, it cannot feed a sufficient quantity of food required to show the expected rapid growth rate, and

consequently, the larger fish only keep frowing faster. In short, the feed given is not utilized efficiently and effectively. The cause of the lare lobs during the cultivation of a group of fish with uneven ,)ody- size is a restilt of "the stronger • prey on tte weaker". lamely, the eels feed on each other. - 19 6-

(5) Management of the Pond • The season in which the shirasu-eel is.turned loose into a pond and trained for feed is the period of the year in which the water temperature varies between day and night and also day to day. Therefore, it is especially important to pay attention to and devise a method to minimize these temperature differences. Especially when the water temperature lowers considerably or it is expected to freeze, vinyl sheets may be stretched over the pond, the quantity of the pond water should be increased to deepen the pond, or to pour warm water such as underground water into the pond to keep the water temperature higher. .If the eels do not feed well during the training and the -r.esidilnl fe, ed wPs -kgs re.mnin at the pond bnttnm i then it often becomes the cause of deterioration of the water quality, when the water temperature rises early in spring. If salt-containing water is used for the pond, this type of water deterioration tends to occur quite readily and therefore, special attention has to be paid to avoid it.. If the phyto- plankton grows thick, then an oxygen content in the pond water may reach a supersaturation level, and the air bubble disease may occur. If a symptom of this disease is observed, a large quantity of fresh, cold water should be poured into the pond at once. On the other hand, if the zooplankton appears in a lare ii.tantity, then the eels suffer from loss of appetite and • start to do "ilria-aen. D:_crefoe, it Lust be re=ved promptly. - 197 -

Spraying an emulsion of dipterex thinly and evenly on the pond surface is quite helpful to achieve the removal. /102 (6) Problematic Points in Rearing Shirasu-Eel The foundation of the eel culturing business lie s . in the rearing the shirasu-eel which is the stock for culturing adult eels, and the possibility of the future growth in a certain area and the potential size of the eel culturing are indeed governed by the quantity and quality of the stock available for further cultivation. It is, therefore, important to study the cause of the periodicity of the haul of the shirasu- eel and grasp the actual status Of the present day haul as well as the long term forecast of the haul. If the haul c'an be forecasted accurately, then the size of business scale can be firmly &stablished,and the lusiness,can.be -operate.da better stability. Production of a better stock for cultivation involves two factors; one is the biological or genetic charac- teristics and the other is technical problems related to producing healthy individuals. At the present tine, the feed is mostly a variety of fresh fish, and securing a sufficient quantity of the feed at reasonable prices is becoming more and more difficult For this reason, an artificial feed or a mixture of this and fish mea must be further examined and production of healthy eels in an excellent Frowth rate should be endeavored. The standard scneC:ule of production of the cultured • eels is feed training in April, and after one year later in the - 198 -

summer, the cultivation,aiming at yota eels, is started. Since 11, the shirasu-eel starts to ascend rivers at the end of October, it should be possible to secure a large quantity of the shirasu- eel by the end of December, although the peak haul may last until the middle of February. Therefore, if earlier feeding and earlier preparation of the stock eel can be achieved, it is not impossible to start the yota cultivation programme within a one year period after catching the shirasu-eel. In order to achieve this, the technique of pounding the shirasu-eel must be improved greatly. If other conditions are good, the shirasu- eel can survive for as long as 150 days without food, but the present status of technology at industrial level is between 10 and 100%, usually between 20 and 50% of the loss rate during the months between December and March. It therefore • appears that a great deal of improvement is to be made in this area also. If the period between the haul and feed training is short, that is, if the shirasu-eels were hauled when the water temperature is about to rise as high as 10°C, the loss rate of the group of shirasu-eels seems to be low. The cause of this large loss is, for one thing, insufficient heat insula- tion against low water temperature of the pound for the cap- tured shirasu-eel, and for another, careless handling at. the haul and during the transportation of the shirasu-eel. By i:dprovement of technology of protecting shirasu-eels during the winter, labor cost may be reduced, the large loss rate can be lowered and the production cost can also be lowered by a • short ocriod producUion 5c,ner;u1c.,, Thee improvements should - 199- - certainly push the status of the eel culturing business forwards and closer to meet the public demand to make the eel as everyday fish diet..

3). Rearing Full Size Eel

(1) Management The eel pond is freshened up every winter and this is called a "winter-haul". This includes disinfection of the pond, grading the eels according to the size, marketing the grown up eels, and returning the rest to the refreshed pond.

When the water temperature rises • o 12 or 13°C in the spring, the eel starts to feed and feed is supplied to the eel pond. Depending on the size of the eels left in the pond /103 over the winter, some fast growing eels can be hauled out of the pond starting early in May. These grown up eels are caught by the "ami-zashi" method or with a drag net. The hauling is done several times before autumn, and later, as the need occurs, younger eels are introduced to the same pond. The - number of the hauling and the quantities of each haul are determined by the managing persons of the . pond and these reflect the final concentrate of the skill in management and technology of the staff involved in managing the ponds. During the feeding period, observation of the pond must be done very carefully. If there is no wind and the sky is cloudy or it is rainini;;, the eels tend to do "hana-age" quite seriously. If there occurs any siim of the chaning- water or diseases, protective measures must be anplied F:l'omptly. In tIlis tIle pond. ',;12ard must; fully exhibit - 200 - • his skill and work very hard. When the water temperature starts to lower in the fall, the eels start to cumulate a thick layer of subcutaneous fat to save energy and nutritional . substances for the hibernation during winter. This is expressed well by the traders' saying of "an eel becomes fat in early fall". Before the eels start to cumulate a thick layer of fat as a source of nutritional substances to be consumed during the fasting in winter, they feed extremely well, and therefore, a large quantity of well examined, fresh feed must be given to the eels. When the water temperature lowers below 800 1 the eels start to hibernate. Therefore, before the water tempera- ture becomes as low as this, or when the temperature is between 12 and 15°Cin between the middle and the end of eovember (depending on the area), the eels are hauled for the winteriza- tion and the ponds are cleaned, disinfected and repaired. In some areas, this is done early in spring depending on the condition of the pond. When this is completed, maintenance and reDairing of the tools and machines, as well as preparation for the next term of eel culturing such as securing a fresh batch of shirasu-sels are done, one by one, during the winter season. (2) Release of the Culture Stock There are two kinds of stock to be turned loose' into the eel ponds; one is the left-over stock and the other is the additional stock. The latter may be further divided into two categories, natural stock and yochu. - 201 -

Left-Cver stock - After the feeding is stopped, the pond is 110 refreshed early in the winter or in November or early in the spring or in March, when the water temperature is about to rise. When this is done, the eels in an eel pond are graded into two groups, one is to be shipped for the market and the other is left in the pond as a stock for the next term of the eel culture. The latter is called the left-over stock. The size of this stock varies depending on the • judgement and plans of the manager, but it is usually between 75 g and 113 g (113 g if the pond is changed in early spring; 75 to 94 g if the pond is changed in winter). Of theSe l the larger size stock may be hauled again in May or June for marketing, and the large majority of the culture stock are hauled around the middle of summer. The smaller ones of this gl, stock may be hauled after summer or may even become a left- over stock again. Additional stock - This is a stock to be added to the near- adult eel pond after May, each time when grown up eels are hauled for the market. It consists of two different kinds of stock eel, each having a different source. One is called yochu, and it is fast to acclimatize itself to the pond and feeds well, but the other, natural stock is slow in catching up on feedinc. The former is a stock cultivated from the shirasu-eel, and the éroup of this stock first hauled in early is called "Iço. 1 childn* or 1 net haul" and this

* "P=s1Jbor's Literlly transln,ted. - 202- group of eels appear to have a genetically excellent growing capacity. There are, of course, Stock eels which do not Grow any larger even after one year of feeding. Therefore, some of the eels of the left-over stock are just about the same size as the "ITo. 1 child". For this reason, the yochu stock should be purchased only from a reliable, honest trader. The natural stock is selected from the small eels /104 captured by the "shibazuke" and "sen" methOds or with a net, and the ones caught by the "nobenawa" method are usually not used as a stock. The size of the eel of this stock is usually between 5 and 20 g. When the eel culturing business is to be started fresh, large sized eels should be chosen as the culture stock .for the ..f.irst yeal.„ 1 .euube1-a then., marketable -,1_ --- produced in the same year, making it easier to recover a part of the capital invested. Quantity of Release: There is a very close relationship between the quantity of released stock and weight increase of the stock eell and the larger the quantity of release is, the more poorly the eels grow, Since the eel .culture is quite an intensive cultiva- tion method, if the fish density per . area of water is made too small, in the hope of higher rate of growth, then the profit also lowers and the profit margin is too small to be a successful business. Therefore, there must be an optimal qunuity of relse. Adjustunt of . tbe best suitD.ble release I n eeri;din eel culuure ponas is perhaps one of the most important conditions to be truly successful in this business. The traders in this business usually set a quantity between 1.1 Kg and 1.9 Kg per 3.3 m2 as the standard, based on their many years of experience. Within this range of the standard quantities, the suitable amount of the release may be determined by the degree of Draoticable tedhnique of caretakers of the pond, availability of the water and so forth. (Table 24) For the purpose of management, by controlling the size of eels after fall, quantity of the left-over stock can be adjusted, and at the same time, it is also possible to make the density Of the eels in a pond high in order to supress the growth of the eels or to make the density low in order to control the quantity of the left-over stock.

.Stock.: The Q•frnrvlarrl nmount ne s tock tn be ndded after hauling out grown up eels may be about half of the quantity of the eels in the pond before starting feeding in the spring. In practice, however, about half of the quantity of hauled eel is added each time when the eels are hauled for shipping during summer season. After the.midsummer days, the traders usually add more quantity of stock eels, but as they usually grow nearly twice as much as the veight in the midsummer days, the exact quantity to be added should be - determined after takinG the price of the stock eel into consideration. (3) Hduling (I)" S=rner iau1irig - There are two ::ethods employed to do

Translator's Note: For the clarity, (1) was changed to (i) and so forth in this section (3) • Hauling. - 204-

the summer hauling; one is "amizashi't. and the other is "ami- biki". Amizashi*: As the eels grow to a marketable size late . in May or early in June, they are hauled for shipping.. The tools and application method vary depending on the area. The net for the amizashi method has a very fine mesh, and is square with a side length of 4 to 8 m. Two opposite sides of the net and the centre are tied to bamboo poles. At the centre of the net, a weight is also attached, and the net is a kind of spreading net. The net was formerly made with cotton twines, but of course it is made with chemical /105 fibres in recent years. Before doing this amizashi, the eels in the pond' • re le, ft starved for one day. As soon as the feeding is started, the eels gather around the feeding post, and when a throwing feed is cast at the centre of the group of eels, they gather tightly at this spot. When the eels assembled, a group of fishermen standing on the dyke thrust the net into the water below the feeding area but not touching the bottom, and another group of fishermen hold and pull the centre pole to lift up the net and haul the eels. . (Fig. 40) It is important not to stir up the bottom soil /106 with the net, because it causes oxygen deficiency. Since a large number oi2 eels iather in a close range, fresh water must • be supplied consbantly Lhirin the oeration, * Translator's Uote: Literally "net-thrusting". ■ - 205 -

Amibiki: This method is applied when the eels do not gather • at the feeding post on the scheduled day of hauling operation, and the amizashi method does not yield a sufficient haul. Size of the net varies depending on the size of the pond, but it is usually 3 to 5 times as large as the net used for the amizashi. It is a kind of drag net with a bag net of smaller mesh at the centre. The net is dragged from the side of the drainage, that is, the deeper side towards the shallow, water inlet side. The hauled eel are placed in a 5 m square pound set near the water inlet. Fresh water is poured in during the operation as for the other method described before. The haul is excellent in a rectangular pond and becomes poorer as the pond shape resembles more of a square. • Usually the dragging motion has to be repeated 2.3 times and at times, this repeated operation results in oxidation of the reduction layer at the pond bottom improving the general environmental conditions of the pond. (ii) Winter Hauling (Pond Refreshening) - • screen door at the drainage is left closed, and the flash board only is opened. When about one half of the pond water is drained, the carp fish, grey mullet and others are hauled with a drag net, and then a bag net is attached to the outlet of the drainage earthen pipe, and the screen door is opened. The eels coming out with the water are collected and transferred to a basket. The eels hidino in the pond bottom may be driven towardr, the draina Te when a none with m3.ny stones tied. at - 206 - intervals are dragged around the pond bottom towards the drainage while there still is some remaining water. There are still some more eels in hiding in the bottom mud. These come out when a wooden T-bar, like the one used to level a fresh cernent floor, is operated on the muddy pond bottom. At times, there may still be some more eels remaining in the bottom mud, because of the weather and the condition of the pond bottom. In such a case, the pond may be lightly refilled with a sufficient quantity of water to cover the bottom, and leaveit until the evening. When the water is drained after dark, the eels may come out more easily towards the drainage. After all the eels are hauled out, lime is applied to the pond at a proportion of 1 bale* per 1 are, and then the bottom mud is stirred well and left exposed to the air.

(Fig. 41)

Since the daily temperature during winter season /107 may -vary following the general pattern of "3 cold days followed by 4 warm days", the day of freshening up the pond should be chosen after carefully analyzing the weather fore- cast. The operation should definitely be avoided if the pond water is expected to freeze. In such an area where the winter temperature is quite low, the operation should be undertaken earlier.

HaulinÉ; of Sinall Amounts of 2e1: During summer, it sometimes bec.:)tr.es necessary to haul only a small amount of eels per day

* Trhnslator's :lote: Probably 60 if not, less than 60 Kg. - 207 - but for many days consecutively. To achieve the objective, it is possible to operate the amizashi method everyday, but repeated application of this method usually causes falling appetite of the eels. Instead, if bamboo tubes are left on the bottom near the water inlet, a nearly constant number of eels can be hauled daily. Three bamboo tubes with 0.12 - 0.18 m of diameter and 0.9 m of length can haul about 3.75 Kg of eel. .(4) Grading Even when a batch of fry produced by the same parents are cultivated under the same conditions, there always occurs individual differences in the growth rate. After three separate groups of shirasu-eels were cultivated for 138 days under the same conditions and feedine methods, there were remarkable individual differences in body length, as shown in the following table. (Table 25) Namely, the deviation in the body length varies between 8.0 and 32.7 cm. That is to say, .even if the same conditions and feeding method areepplied to cultivate a group of shirasu-eels, the growth rates vary between 9.81 and 15.93%. As the pajor factors which cause this deviation, density of the eel under cultivation, amount of feed, biological and L;enetical factors specific to living animals, growth-inhibitory etiolocical factor, size of the eel under cultivation, period of cultivation nr.d so for ;h can be considered. Thus, che of 4 11e _row -th rate bec,-mes - 208 -

more pronounced as the period of cultivation becomes longer. Therefore, if the cultivation is cOntinued under such conditions, the results are to be expectedly poor. It is ideal to grade the eels in a culture pond frequently, and to release each group of eels of the same size in a different pond, but it is difficult to practice that under ideal conditions, because of the labor involved, and various other problems related to the management. Accordingly, the gradings are customarily done at the summer hauling and winter hauling. When the grading is done at the summer hauling, it must be performed quickly in the water using a grading machine. Depending on the market value of the eels at the time, the standard zf the grading .should_be,set tz_choose the _eels with commercial values. If a grading machine is not used, a small number of eels are taken out of the pound set near the water inlet and transferred to a "hanging basket" and the ones to be returned to the pond and the one to be taken out of the pond are selected and separated. The standard of grading is about /108 150 eels per 15 Kg. At the winter hauling, the stock eels to be returned and the marketable eels are separated, and the latter group is further divided into two classes, average (112 - 150 g) and boku (more than 120 g). The stock is released into the pond as soon as the • jradin is completed, and te eels t:o be shippd are. sub,:;ected - 209 - to the "iki-shime" procedure. The grading bench is divided into 2 sides length- wise from end to end along the centre line, and on one side of the bench and above the bench top, a funnel like box with about 1 cubic meter of volume is proveded. The funnel is used to retain eels poured from a basket, and has a small outlet from which eels come out on to the grading bench. The eels are grouped on the bench into three groups, the stock to be returned to the pond, sick eels, and boku to be shipped to the market, and each group is placed into three. separate baskets. Some grading benches have holes along the centre line, and instead of placing the groups into baskets, they are put through the holes which lead to separate containers. When quantity of the eels hauled by the dragnet method or sashi-ami* method for grading is too large to process in a short period, the eels are first placed in a pound basket to let them rest a while, and a small number of eels are taken out at a time for the grading. When this is done, it is important to handle the eels slowly and gently, because a sudden change of environment always causes abnormal excretion of the mucus. To handle the eels gently, the pound basket is lifted from the rest place, and placed near the grading bench and after about 10 minutes, 2 or 3 bucketfuls of water are poured over the cover basket, and let it drain ell. Only when white. butobles (due to the nucous liquid of the ee1s) •sbIrteJ to .1:,cwoIlbth tbey &re placed on the

* Translator's Note: Undoubtedly a synonym of "ami-zashi". - 210 - grading bench. (Fig. 42) (5) Disinfection At least once a year, the eel pond must be refreshed. If the pond is freshened up when the eels in it have been doing "hana-age" or the "changing-water", then the pond must be disinfected after the water is drained off. /109 (Fig. 43) • When the disinfection is carried out, it is desirable to have ample time to spare. Since the haul at the pond refreshening can be estimated by the amount of feed consumed and the time required to complete feeding, an exact number of baskets needed should be ready on hand. As soon as the water is drained off In the morning, the pond bottom is stirred well and lime is sprayed. After a whilel eels which are thought to have been hauled out but still remained in the mud start to make desperate efforts to avoid the lime. When these are captured, there is no more live eel remaining in the pond bottom. If these eels are left in the pond at this stage, when the pond is refilled with water and the new culture stock is introduced, the eels left in the Ponds at the pond refreshen- ing pre.y on the smaller stock eels, especially on warm days after the cold wave of the 3 cold and 4 warm day pattern during the winter. It is also (lei2Dble to expose the botton soil to the sun at least for I day. By doing this, the epidemic diseases which may break out in early spring can be avoided to some extent, and the organic matei.'ial mixed in the soil and the resulting reduced layer of the.soil can be oxidized and

consequently, a favorable set of environmental conditions or the phytoplankton may result. 4) Various Eel Culture Methods (1) Running Water Modification of the Standard Eel Culture Method Productivity of the standard eel culture method, • that is, the still water model, was between 1.88 and 12.45 Kg per 3.3 m2 , average 7.44 Kg per 3.3 m2 1 in Yoshida area before the war, but after the war, the same area recorded the produc- tiVity between 3.98 and 14.48 Kg, average 8.36 Kg. This increase of productivity was mainly due to the improved method of oxygen supply into the pond water. However, this technical advancement does not promise any further imDrovement in the yield. In order to obtain a better yield above this limit, it is necessary to adapt a running water type modification. In fact, already in 1923 and 1924 and 3.180 later, fj.sher_ies testings stations of Aichi and Kanagawa prefeCtures carried out experiments on the running water modification of the eel culturing method. However., the results were not very promising. After the war, Hamanako Branch Station of Shizuoka- prefectural Fisheries Testings Station started reexamination of the application of the runninG water model of the eel culture method, in 1956. It was reported that, when 635 shirasu- eels wece fed with ito-mimi2;u (thread-like earthworm), short- neced clm ment snd fish ret for 197 (b.y . from Pebruary 15th - 212 - • In a small water tank, while fresh water was poured into the tank at a rate of 15,e per hour increasing to 180L per hour as the eels became larger, the yield rate was 70%, weight increase ratio 45.6%, and feed coefficient 5.3 (Egusa and Ohtsuka, 1957). When experiments on the same modification were carried out in a field test scale, that is each of the

three groups of eels, 4 Kg, 3 Kg or 2 Kg of eel in one group, 2 was released to a 3.3 m pond separately, and fed with frozen fish meat*, while water was poured in a rate of at least 1,380 î per hour, the weight increase ratio was between 52.1 /110 and 66. 62%, weight increase coefficient** between 4.27 and

5.30, and natural decrease rate between 0 and 0.55%, all of which were nearly the same as obtained by the still water gl, method. These results indicated a very bright future for thé running water modification, especially because .the quantity of the running water and the . feed efficiency can be improved much More. Later, the Hanako Branch Station group obtained (1966) the weight increase ratio between 66.8 and 83.7% and - feed coefficients between 1.62 and 1..67 by feeding with a mixture feed*** for 135 days at a water poùring rate of between 55 and 60 £/min. (Inaba and others, 1959) The optimal quantity of the eel under the running water model of the eel culture method was proposed to be

between L350 and 2,500 Kg per 100 m2 pond surface at the water

* Uote: For how long? ** 'Jjranslato .2'q. ote: Perhaps a feed coefficient. ** 1' Trarlslator's Altholih not specified, it appears to be an arti.ficial or cIrtificial mixture 1e cd.

ZS" - 213 - temperature of . 0°C (Saeki, 1959). .This modification at this optimal condition has been widely applied in Taiwan and yielding excellent results. .(2) Tunnel Model of the Eel Culture Method This modification is based on the eel's nocturnal and hiding characters. It has advantage of the intensive production which is the same as that of the running water modification, and at the same time, as it involves only a small risk of change of the water quality, management of the pond is easy. It can also utilize the hot spring water to control and regulate the water temperature and therefore, the eel can be fed during the winter also. Although this modified method is suitable to adopt in a narrow land, it requires a large quantity of water. Water is filled into two concrete tanks, one for water inlet and the other for outlet, with 1 m 3 or 1x1x1 m (water depth 60 cm) of capacity and a connecting earthen pipe, 5 m of length and 23 cm of diameter, to 60 cm of depth. This is one unit of the culture pond, and the water poured into the inlet tank runs through the earthen pipe. and overflows through the outlet tank. When fish meat was given to the eels in this system, while the water, 20 - 22°C, was poured through at a rate of 2.0,e per minute, the weiht ircrease ratio per day was between 0.58 and 1.35, average 1.0%, and the feed

coefficient was between 3.58 end ?. .4 5 average 4.4. During winter, hen the water teuir)erature was adjusted to 26°C, the - 214 -

weight increase ratio per day was between 0.43 and 1.27%, average 1.05% and the feed coefficient was between 3.51 and 8.50, average 4.86. The capacity of this system was calculated 2 as about 15 Kg per 3.3 m * if the amount of the dissolved oxygen, at the water outlet, is at least 2 cc/L, and the flow rate of the water is 500,12. per hour, and about 30 Kg if the flow rate is 1,0002 per hour (Noguéhi et al, 1959). (Fig. 44) - Ito (1962) reported that the productivity and capacity of this saine type of pond were more than ten times higher than those of the standard still water pond in Hokkaido, when the water temperature was adjusted to 2300 . (3) .. Circulatory Eel Culture Method • There are a number of restricting factors in securing a sufficient quantity of water needed for the eel culture. In order to lift these factors, and also to develop more highly intensive culturing methods utilizing the smallest area available, this method has been developed. Since the method utilizes the water repeatedly and for a prolonged period, control of the water quality is relatively easy. On the other hand, the investment cost and maintenance expense /111 become quite high if higher filtration efficiencies are desired. Saeki (1958) used a small . circulatory water tank to cultivate the shirasu-eel for neriods between 136 and 203 • days aild obtained the weiFYit increase ratio between 42.1 and * Translator's Note: Could this be 3. 3 m 3 ?

''7!'",rrnrrrrr:' - 215 -

57.5, feed coefficient between 5,3 and 5,7, and density of eels in the tank between 4 and 5%, that is, more than twice as large as in a pond with the same size but non-circulatory, Mie-prefectural Fisheries Testings Station carried out a developmental experiment in an industrial scale, at its Ise Branch Station. The circulatory pond facilities occupied 59.84 m2 of the total. area, and contained 64.27 m3 of the total water, and the water was circulated at a flow rate of 41.022 m3/hr l and the pond water was exchanged at a rate of 18.5 times per day. Of the total area, the pond occupied 50%. The test results showed that, if the pond could produce 38.3 Kg ofeel per 3,3 m2 , the circulation method was economically feasible, and this limiting productivity of the eel is equivalent to between 1.57 times and 2.35 times the eel density in a still water pond (Suzuki, 1954 - 1964). (Fig. 45) The same developmental work was carried out by Nishimikawa Eel Culturists' Cooperative Association for a period of 91 days, and the weight increase ratio was between 41.1 and 94,0%, and the feed coefficient was between 1.25 and 1.50, Saeki (1959) considered that the optimal quantity of eel to be released to a circulatory pond was 350 Kg.' (4) Salt Water Method Since the eel can live in both fresh water and salt water, it should be possible to use sea water in an eel pond. In fact, in the field of natural water where the eel can choose to live on either side of fresh water or sea water,

• - 216 -

the larger quantity of eels can be hauled from the sea water side and close to the shore than from the fresh water in inland water basin. The reason that sea water has not been used to culture eels is that environmental factors tend to vary quite considerably when sea water is used in intensive culture method as in the pond culture. The most hazardous water change of the sea water pond is generation of hydrogen sulfide. While there is oxygen at high concentration, hydrogen sulfide generated can preciDitate as sulfidesand,therefore, it is not toxic to the eel. If, however, the oxygen concentra- tion and pH of the water lower, sulfuric acid-reducing organ- isMs liberate hydrogen sulfide from the sulfides. Since there is much larger sulfides already contained in sea_water than in fresh water, the chances that hydrogen sulfide is liberated in the water is much larger ln the sea water pond. Hedrogen sulfide is not only toxic to the eel by itself at low concen- tration but also synergetically toxic with carbon dioxide and ammonia when their concentrations become higher in the water. Lowering of the oxygen concentration also.inCreases the toxic property of hydrogen sulfide. Therefore, the most serious problems related to the use of sea water as the pond water are oxygen deficiency and pH lowering, and these must be solved

before the use of sea water becomes practicable. When sea /112 water was used in an experimental run of a pond with semi- runnin::: water modification, at . a flow rate of 21., per minute, tbe water (ualiby deterioraed in about 2 weeks, but in a • 17.,ori with ideal runnin wat.:-c modification, the weir2nt increase - 217 -

ratio was 24.0 and the feed coefficient was 6.04. The results • of the latter system were regarded to be successful in meat increase, feeding and growth .(Hamanako Branch Station of Shizuoka-Prefectural Fisheries Testings Station, 1964). Beppu Institute of Fisheries Multiplication Research (1964) in Kyushu was successful in industrialization using 3 sea water tanks, each with 1.1 m 3 capacity and at a flow rate of 12 m 3/day. According to their procedures, the shirasu-eel showed quite normal growth rate until July. The use of sea water would be even more effective if a net-pound method is applied on the sea surface. (5) Net-Pound Method When the eel culturing business is operated, a large capital investment required to build ponds and avail- • ability of a large quantity of water are restrictive conditions in expanding the business scale, In order to reduce this restriction, the eel may be cultivated using a pound built with a net and set in a lake, pond, inland bay, or in the sea near the shore. This method requires relatively smaller amount of capital investment and the business can be operated in a small scale. In Hamanako, a net pound is built with two 2ayers of net; the outside net is a vinyl-coated wire net (50 mesh

per 33 cm) and the inside net is a moji-net (105 mesh per 33

cm) made of saran*. The pound is made in a size of 2.0 X 3.0

x 2.0 m and it is tied to 4 buoys made of foamed styrol. • * Translator's Note: Trade name of synthetic fibre? - 218 -

When the eels in this pound fed on fish meat for one month while the average water temperature was 25.4°C, 77% of the total eels turned out to be marketable, and when an (artificial) mixture feed was used at water temperatures between 19.1 and

24.8° , the meat increase ratio was 79.04% and the feed coefficient was 1.56 in a one month period (Hasegawa, 1964). According to the results. obtained by Akita-

Prefectural Fisheries Testings Station (1968), small eels With about 20 g of body weight can be released into a pound built with a 3.8 mm mesh. If a resting place is built at a half depth, i.e., 1 m if the depth of the pound is 2 m, then more than tWice as much of the culture stock can be accommodated as the rest place assists the eels in avoiding the deep, low oxygen layer in the pound. Tanaka (1967 - 1968) reported that the density of the accommodated eels in this pound in the sea could be 7 to 14 times as much as in a fresh, still water 2 pound per 3.3 m water surface in 1965, and it was 33 to 132 times as much in 1966. The weight increase ratio was between 46.4 and 140.0% in 1965, and poor in 1966. The feed coefficient in

1965 was between 7 and 15, and in 1966, between 8 and 12, which - were not greatly different . from those in the fresh, still water pond, eventhough the density of accommodation was extremely higher in this pound method. ) Eel Culture 1:ethod Usin=- Hot Spring ';Jater As the eel is either tropical or temperate, it re,)uirc2s at least 10 °C for feedin activity. In this country, nnly hnt ;-,3 -)2ij water or rour,t:lin water can be utilned to keep the eel under feeding conditions in winter. In Shishuku

" - 219 - • area of Kagoshima-prefecture, high temperature water, between 40 and 45°0, is available throughout the year. Using this hot water, the eel cultivation can be carried out .during winter with excellent results, but during summer, the water tempera- ture must be lowered. This is done by spraying the hot water on a pile of brushwood*, and it cools down the hot water to about 30 0 because of the loss of heat of evaporation. In addition to the hot water, either cold or normal temperature - .water is required in a very large quantity. (7) Planting in Lake The first example of transporting eels and turning /113 loose in lakes and ponds at the destination was recorded in 1883 and 1884, when eels were transported from Tokyo to Aomori-prefecture. In later •years, paanting of eels became quite popular in Tohoku prefectures specifically along the Japan Sea coast. Major lakes and inland bays where the planting has been carried out often are the Lakes Biwako, Suwako, Kamoko, and the Inland Bays l Hachirogata, Hojozugata, Tomochigata, Kahokugata, Imaegata and others, and the eel stocks turned loose in these lakes and inland bays have about 10 g of body weight, hauled or prepared in Aichi, Chiba, lbarakr . and Miyagi prefectures. They are planted in spring and harvested when they wed41 about 100 g. Tools for hauling the product eel are bamboo tubes, sen, and nobenawa in the lake and a weir 2,-nd lon bas net for the eels swiu, towards the ocean.

* Translator's Eote: Probably placed on a scaffold over.a pond to let - watr run U1-1;»,-)uh. - 220 -

The effectiveness of the planting in the natural lakes and inland bays is expressed.by the ratio of the number of eels hauled against the number of eels released. In the Lake Biwako, it is about 21* and by the weight ratio 5, and in Suwako, it is 7.2 by the weiijlt ratio (Tauchi and Miyoshi, 1936). The number of lakes in Which eels were turned loose in the years between 1929 and 1931 were 28 in 18 prefectures out of the total 723 lakes in this country, and quantity of the stock released are about 910 thousand eels. In the Lake Yogo, the ratio of the haul against the stock eel planted was

(8) Planting in Rivers Fresh water hauls in this country amount to 97 thousand tons, of which 54 thousand tons are hauled in rivers. The quantity of eel hauled in fresh water basins is about 17 thousand tons. The eel hauls of all the fresh water basins in this country excluding the Japan Sea side and north of Mt. Kinkazan along the Pacific Ocean Side before the artificial plantinÈ; was started and the same, but after the artificial planting age were compared. The data showed that the amount of hauls resulted after the artificial planting should be about 4'.),1 tons, by the difference of the afore-cited two sets of data. Since the nunber of stock eels turned loose in these rivrs was about 100 thousand eels per year, and therefore,

* Translator's rote: Per 100 stock eels? ** Translator's Note: it is not clear if the figure is based on weitsht or number. - 221 - even if there were some stock eels released to these rivers by private source, not belonging to the fishermen's association or cooperation union, the rate of natural loss during the period in which the released eels stay in rivers was estimated to be quite small, that is,.the rate of recovery or the haul was very high (Tauchi, 1943). - 222 -

II! 10. MARKETING 1) ikishime (ikekomi) Ikishime is applied to the marketable eels before shipping in order to remove the fat specific to the kind of feed given while under cultivation and cumulated in the eels' body and to improve the taste of the eels, and also to prepare the eel to be transported safely. The effects of ikishime on the eels are làss of body weight and change of meat quality. The weight loss is the more pronounced change of the two. First, within 10 days of ikishime the eels loose weight dramatically, and about 80% of the total weight loss occurs in this 10 day period. During this period, the earlier 11› the date is, the higher the weight loss is, and after the 20th day of ikishime, little weight loss occurs. In fact after the 20th day, the loss is only 0.1 or 0.2% per day. The weight loss is also related to the water tempera- ture, and it is average 0.2%* per day in summer and 0.1% in winter.

(Table 26) (Fig. 46) /114 Death of the eels during the ikishime period is /115 also related to water temperature and season. During summer, while water temperature is high, death starts to occur after the 20th day of ikishime and on around the 50th day, the

morbality reaches as high as 7 0% . Regarding the change of the meat quality, as the

* Translator's Note: It is much larger than:this by Table 26 and Fi. 46. - 223 -

period of ikishime prolongs, a relative quantity of the water content in the meat starts to increase, and a relative amount of dried matter in the meat decreases. In the dried matter of the meat, relative quantities of ether extractables decrease while quantities of ash and total nitrogenous matter increase.

This is to say, decrease of the dried matter during ikishime is caused by the loss of ether extractables. The fact that the loss of body weight, that is, .loss of various bodily components during the initial period of ikishime is quite large means that the effects of hauling the eels, transportation, pond refreshening and other handlings of the eels are quite serious, and therefore, it strongly indicates that the eels must be handled very carefully and ,gcntly.. _Degree of.the loss of various meat component is also governed by the degree of metabolism at the temperature of the water, and therefore, the rate of loss is high in summer and low in late autumn. However, the progress of loosing these body components does not proceed uniformly but rather quite irregularly. • (Fig. 47) During the ikishime period, it is known that the body fat is always consumed more than protein is The calorie /115 consumption of the eels during the ikishime period is between 10 calories and 33.4 calories per day per Kg body weight in summer and between 7.4 and 24.1 calories in winter, while the eels l'recedure of 'evural rethods are applied to achieve - 224 -

the purpose. They are, to place a basketful of eels in a cold running stream called "soaking place" after several days of fasting, to place the basket in a small pond to which fresh oxygen-rich well water is poured constantly from one side, and to pile up a few of the baskets and keep the baskets showered with cold and fresh well water from the top and let it drain through the bottom basket.

(Fig. 48) When the baskets containing water have to be piled up, first a rubber plate is placed on the bottom of the basket .

and about 4 Kg of the eel is placed in it. Lately, however, a very durable, light-weight container made of synthetic resins has been used more commonly. It is important to make it certain that the fresh water runs throu.gh the basket when the hn..kp-hs are placed in a stream or pond. It is also important that at least a portion of the basket is exposed to the air, when the basket is soaked in water. By doing so, eels can breathe the air if they need to. Therefore, the bamboo basket should be suspended in such a way that the water level is below the cover of the basket. It is to be noted that, if the basket is placed on the bottom of the river or pond, then the oxygen cannot be supplied from the bottom side of the basket. The important

points of ikishime are to reduce the fat and chan g e the fat

quality under a condition in which oxygen is fully available , nerefore, whatever procedures-are taken, these key points should not be for,ptten. ni;s,-ht Èlso be L;ood to spray water • 1311 around th basket by of a jet spray device, - 225 -

When shower is used, usually 1 or 2 daYs showering is sufficient to fulfill the purpose of the ikishime. Under these conditions, about 4,000 Kg of adult eel can be processed for ikishime in 3.80 m 2 area. 2) Packing and Transportation The most commonly applied method is to divide 19 Kg of eel in 4 baskets to be piled up one on top of another, in such •a way that the top basket contains the largest quantity of eel and the bottom basket the smallest que.ntity, and place 8 Kg of ice on the cover of the top basket in summer and in other seasons, 4 Kg of ice. The-whole set up, baskets and ice container, was then tied with a rope and shipped. This method guarantees survival of all the eels for about 10 hours of transportation Modern method is to use two vinyl bags, 70 x 26 cm, each containing 10 Kg of eel, and fill up the bags with oxygen and a small amount of ice, and to pack the two bags in a cardboard box, 30 x 35 x 65 cm. This method is quite reliable and all the eels packed can survive for 30 hours during the transportation.

•

- 226 —

11. MANAGEMENT In the eel culture busines, technology and manage- ment are inseparably related to each other, and only when both of them rotate like a pair of wheels of a wagon, the business becomes stabilized. The technical part of the eel culturing business involves a prompt, correct and accurate handling of various changes caused by weather and other natural environment based on the substantial experiences cumulated in many years and steering of the sequence of the eel cultivation steps along the line of the providence of nature. When the operation is to be newly started but, both capital investment and operational expense must be • -secured, bu l-after the econd,year, the-cost is-mostly in the category of operational expense, of which feed cost and cost . of culture stock are the major items. Particularly, the feed cost takes almost 70% of the operational expense, and there- fore, the quantity, quality and cost of required feed are the most important items in the management of the eel culture business. Among the capital investments, the major portion is expended for building the ponds. When a modern bulldozer is used, the pond building can be done in a short perio4 and it rental including the operator's labor is about 3,500 to 4,000 yen per hour. The,time needed may be about 18 hours - to build one 99 m 2 pond, and for building dykes and facilities 111› Cor water inlet and drainage may require between 10 and 13 - 227 -

2 2 man-days for one 99 m pond. A simple, 3.3 m wide feeding

post may be built at•a cost of about 10,000 yen. The well

with a 3 HP motor and 4 inch pipe may cost about 150,000 yen,

if the pipe length is about 50 h. In addition, several items of equipment may be required. They are nets, baskets, motor, water-stirrer, vertical pump if required, wagon and others. The cost of the culture stock can be calculated,' if the size of the culture pond is determined, that is, by taking the standard quantity of stock to be turned loose at

a range between 750 and 1,900 g per unit* pond surface, and multiplying the total surface area of the pond with this standard culture stock quantity required. Although the amount • of additional stock to•:be -released into -the pond later varies considerably depending on the skill of the technique, it may be assumed roughly as one half of the original culture stock. Of

course, this quantity is deeply , related to the quantity of the eels hauled out of the pond. It is extremely important not to economize the cost of the culture stock. Poor stock for cultivation should never be purchased. Since the quality, good or bad, of the culture stock is directly related to the results, even if the

cost is hizher, only a better clality stock should be looked for and purchased.

* Traslator's 1:;ote: seciried here but perhaps 3.5 :a- • uFually quotcd by the author. - 228 - • Selection of the size of the stock eel and determination of the release quantity per unit area are deeply related to the technological and managerial capabilities of an eel culturist responsible for operation of the business. Generally speaking, it is desirable to choose large-sized culture stock in the 1st year of the operation but after the 2nd year, the size should be determined based on the left- over culture stock, that is, the eels returned to the pond after grading for further cultivation. If the left-over stock consists of fairly large-sized eels, then the new batch of stock eels must be rather smaller ones, because, otherwise, if all grow well in the following cultivation period, a large portion of the eels in the pond are to be marketed before the • midsummer days. The price of eel varies throughout the year following a certain pattern. It usually is highest around the midsummer days, and also a little high just before the New Year's Day. The lowest price occurs in the middle of November or the middle of March when a large quantity of eels must be shipped out because of the pond refreshening. Therefore, the timing of the pond refreshening is certainly related to the managemental problems in this business. In short, the marketing should be done in a very positive attitude and quickly, if the market nrice and its change and the comoetitors' attitude on the shipoin'are a Food price for one's product. 'D 'DO ••••

An annually required quantity of the feed can be obtained by the following equation. . Amount of released culture stock x (3.5-1) X 6 where, the weight increase ratio is taken as 3.5. If a few different kinds of feed had the same quality, of course, the cheaper feed should be chosen. Feeding the eels with high quality but cheaper feed efficiently and economically is the key point in the eel culturing business. Securing a sufficient quantity of such a cheap and yet high quality feed is the managerial skill required for the business, and feeding the eels with the cheap and high quality feed most /1 19 economically is the technical skill also required in the sUccessful eel culturing business. It is no exaggeration to say that the proficiency • in technical matters related to the eel culturing business can be judged simply by the skill . of feeding the eels. Since the annual quantity of feed consumption is a sum of day to day feed quantities, the quantity of daily feed can be regarded as the fruits Of one's technical proficiency. Generally speaking, the standard quantity of daily feed is between 7 and 12 percent of the quantity of the eel in the pond, if the eel is adult, and this standard quantity varies depending on size and age of the eel. This is, however, strictly a standard value to be fed in one day, and it should be chanif,ed in consideration of the weather of the day, the

feeding condition on the day before and earlier and so forth, • In short, the hiCest standard of the technical nroficiency in - 230 -

ecl culturing business, which is reflected exactly in the :c, fitabilitY of the business, is to feed, the eels four-fifths full everyday depending on the day's miscellaneous conditions which vary from day to day. The number: of summer-hauls as well as the quantity of the culture stock to be added each time after the haul are also very important technical problems to raise the profitabi- lity of the business. REFERECES

• Toshi INABA, 1959: Eel Culture Illustrated (Yoman Tokuhon). Published by Narahara Fisheries Multiplication Cooperative Association (Narahara Yoshoku Gyogyo Kumiai).

Isao MATSUI, 1952: Studies on Morphology, Ecology and Cultivation of Japanese Eel. Research Report of the Second Fisheries College, Department of Agriculture and .Forestry (Norinsho Daini Suisan Koshusho Kenkyu Hokoku) Vol. 2, No. 2

Isao MATSUI, 1961: Essay; Lifelong Journey of the Eel (Zuihitsu; Unagi no Tabi) Published by Zitzugyo no Nippon Co., Ltd., Tokyo.

Seminar of Fisheries Multiplication (Suisan Zoshoku Danwakai), 1959: Fisheries Multiplication, Special Issue on Eel Culture (Suisan Zoshoku, Yoman Tokushu). Fisheries Multiplication (Suisan Zoshoku) Vol. 6, No. 4. • isao'MATSUI, 1967: -CUltivation of Eêls '(Unagi no Yosei). Fish Culture (YogyoE.aku) Details (Kakuron).

• - 23 2 -

11, Brief Surveys of the Author's Career

Isao MATSUI

Graduated from Fisheries College (Department of Fisheries Multiplication), Department of Agriculture and Forestry in March, 1924.

Research Assistant of the Same College in April, 1924.

Assistant Professor of the Same College in 1941.

Professor of the Same College in 1947.

Presently Professor of the Fisheries College (formerly the 2nd Fisheries College of the Dept. of Agr. and Forestry) and Chairman of the Dept. of the Fisheries Multiplication of the • Same College, Doctor of Science: February, 1952; Title, Morphology and Ecology of Japanese Eel.

Award of the Agricultural Society of Japan: April, 1954; Title, Studies on Morphology, Ecology and Cultivation of Japanese Eel.

rAMTleellPfnMee7eXer7:5M ;N - 233 -

Publications of Japanese Association of Protection of Marine Resources (Nippon Suisan Shigen Hogo Kyokai Kankobutsu) (Already Published) [Fisheries Research Series (Suisan Kenkyu Sosho] (1) Yellowtail Fish Resources in the Vicinity of Japan, by Fumio Mitani (or MITSUYA) of Western District Fisheries Research Institute. (2) Studies on the Mesh Sizes of Dragnets, by Tsuneo AOYAMA of Western District Fisheries Research Institute. (3) Bottom Fish Resources in the East China Sea and the Yellow Sea, by the Bottom Fish Group of Western District Fisheries Research Institute. (4) Mackerel Pike (Cololabis saira) Resources, by Hideyuki HOTTA of Tohoku District Fisheries Research Institute. (5) Ecology of Ma-sardine Fish, by Keiichi KNODO of Tokai District Fisheries Research Institute. (6-1, 2, 3) Salmon and Trout Resources in the North Ocean, I, II, III, by Tomonari MATSUSHITA of the Fisheries Agency of • Japan. (7) Retention of Freshness of Hauled Marine Products, by Eisaburo (or Eizaburo) NOGUCHI of Tokai District Fisheries Research Institute. (8-1,2) Ecology of Bonito and its Resources I, II, by Ken (or Takeshi) KAWASAKI of Tokai District Fisheries Research Institute. (9-1,2) Nutrition of 72ish Culture Feed I, II (Enlarced and • d), by of Tokyo Universit and Tomotoshi OKAICHI of Kagawa University. - 234 -

(10-1, 2) Tuna Resources of the '::orld I, II, by Hiroshi 7:A1ANURA of Hoko Fisheries Co. Ltd. (11) Bottom Fish Resources in the Korth Ocean, by Osamu KIB7MAKI of Tokai District Fisheries Research Institute. (12) Floating Fish Resources in the East China Sea, by Tokimi TSUJITA of Tohoku District Fisheries Research Institute. (13) Usefulness of Drift Seaweed in Fisheries, by Tetsuji SENDA of Okayama Prefectural Fisheries Testing Station. (14) Live Fish Transportation by Hitoshi MOROOKA of Nagasaki Prefectural Fisheries Testing Station. (15) Effects of Industrial Wastes on Fisheries Industry, by Tadao NITTA of Tokai District Fisheries Research Institute. (16) Sagittated Calamary Resources, by Hisao SHINNYA of. • Northern District Fisheries Research Institute. (17) Live Fish Transportation of Fresh Water Fish, by Takayoshi YAMAZAKI of Nagano Prefectural Fisheries Guidance Office. (18) Ecology of Mackerel and its Resources, by Shuzo USAMI of Tokai District Fisheries Research Institute. (19) A Study on Estimated Fisheries Hauls in Rivers, by Seiichi KATO of Developmeht of Power Resources Co.,Ltd. [Fisheries Itiltiplication and Cultivation ,eries (Suisan Zoyoshoku Sosho] (1) Construction of Fi.sheries VultiplicatiOn and Cultivation Grounds based on Civil EnGineerin Technolow, by Tokuichiro TAivERA of 4. ricultural ..esearch' institute, Shieki • vAADA of Aricultural ThCineeriesea1ch institute, - 235 -

(2) Uakame Seaweed (Undaria Dinnatifida) Cultivation (Revised Edition), by Yunosuke SAITO of Tokyo University. (3) Improvement and Construction of Seaweek Culture Facili- ties by Civil Engineering Technology, by Takeo KURAKAKE of Aichi Prefectural Fisheries Testing Station. (4) Theory and Practice of Eel Culture, by Isao MATSUI.of Fisheries College. (5) Artificial Hatching of Trout and Salmon, by Takeo MIHAR and other(s) of Hokkaido Trout and Salmon Hatchery. (6) Culture in Mutsu Bay, by Gotaro YAMAMOTO of Yamagata University. (7) Scallop Fishing along the Coast of the Sea of Okhotsk, by Shigeru ITO of the Department of Fisheries of Hokkaido Government, (8) Artificial Fish Reef, by Yasuo OSHIMA of Tokyo University. (9) Cultivation of Coastal Seaweed, by Toshizo SUDO of Tokai District Fisheries Research Institute. (10) Prospect of Fisheries Industry in the Ariaka Sea by Ya IKESHE of Western District Fisheries Research Institute. (11) and its Multiplication and Cultivation, by Shun INO of the Fisheries Agency of Japan. (12) Culture by To MATSUI of Fisheries University. (13) Swellfish Culture by Atsushi FURUKAWA of Tohoku District Fisheries lesearch institute and Tohoru OKAMOTO of Naikai District Fisheries Research Institute. (14) Artificial lic.tclrij of ':)alnon in Japan, by Tetuyuki AU-n of Ho',;kide 2rjut; L:m1 :S.airon Hatchery, ":.: , eizo nUO of

- 236 -

Hokkaido Trout and Salmon Hatchery, and Kisaburo TAGUCHI of Nichiro Fisheries Co. Ltd. (15-1, 2) Environment of Shallow Water Culture Grounds I, II, by Tadashi TAMURA of Hokkaido University. (16) Design of Fisheries Facilities, by Yukimitsu YOKOYAMA of Nippon Steel Pipe Co., Ltd. (17) Fish Road and Fish Ladder, by Seiichi KATO of Electric Energy Source Development Co., Ltd. (18) Cultivation of a Yellowtail, by Atsushi MINAMISAWA and Hiroyuki SAKAI of Ehime Prefectural Fisheries Testirw Station. (19) Various Problems related with (Penaeus laponicus) culture Technology (to be published sOon), by Kunihiko'SHIGENO of Kagoshima Prefectural Fisheries Testing Station. (20.) Multiplication of an Octopus, by Kiheiji INOUE of Suma gl› Aquar um. (21) A Sea Urchin In Hokkaido and its Multiplication, by Akira Fuji of Hokkaido University.

[Overseas Fisheries Series (Kaigai Suisan Sosho) (1) Artificial Reproduction of Trout and Salmon in U.S.S.R., by U.S.S.R. Literature Tram3lation Group of Fisheries Ai_ency of Japan. (2) Oceanic Fisheries of Communism China, by Shigeaki SHINDO of estern District Fisheries Research Institute. (3) Pisheries Policies in nritain, ',lest Germany and Uorway, by Akira A2r2,2U of Fisheries Acency of Japan and Punji • IY=1= of 77tional Feder{ltion of Fishermen's Association. - 237 -

.M Fisheries Industry of U.S.S.R., by U.S.S.R. Literature Translation Group of Fisheries Agency of Japan. (5) The Course of Development of Passing Kihada-Tuna Control Law of the U.S.A. in 1962, by Ryuzo OMURA of Fisheries Agency of Japan and Tatsuya of MIMURA (or MITSUMURA) of Fisheries Agency of Japan. (6) Reserve Fish Policy of the U.S.A., by Kazuo MIYAZAKI of Japanese Association of Whale Fishing. (7) Circumstances of Protection of Resources for Inland Water Fisheries in North America, by Giichi YAMANAKA of Fisheries Agency of Japan, Ryoichi YAGI of National Federation of Fresh Water Fishermen's Association, and Raiei TSUCHIDA of Kaigai Gyogyo Co., Ltd. • (8) Policies on -Prevention of Water PollutiOn in Western European Countries, by Kazuo INOUE of Fisheries Agency of Japan. (9) Bartlett Law, by Gonji ITANO of Fisheries Agency of Japan. (10) Tuna Fishing in Taiwan, by Hiroshi NAKAMURA of Hoko Fisheries Co., Ltd. (11) Fisheries Industry of Cambodia, by Hoichi SHIRAISHI of Fresh Water Fisheries Research institute. (12-1, 2, 3) Fisheries Industry of Korea I, II and III, by Korean Fisheries Research Group of Fisheries Industry of Japan. (13) Anchobi Fishing and Fish Meal Production in Peru and Chile and Shrimp Fishing in Mexico, by Katsumi SAKAMOTO of japanee t:eder3ion, of 7ish,,.12 Association, Yukio WU (or Gi;DA) of risheries Agency of Japan, and :)etsuo WATAbE of Taiyo Fisheries Co., Ltd. - 238 -

(14) Problems Related to International Fisheries Industry and • Oceanic Law, by Fukuzo 1;AGASAKI of Tokai District Fisheries Research Institute. (15)Fiàheries Industries in Western Malaysia and Singapore (Malay Peninsula), by Masao AKAI, Shunnichi HOZUMI and Masatsugu FUKUYA of Fisheries Agency of Japan.

[Fisheries Policy and Administration Series (Gyosei Sosho) ] (1) Present Status and Problems in Policies of Water Quality Retention, by Motokichi MORISAWA of 2isheries Agency of Japan. (2) Present Status of Improvements 'of Fisheries Industries, edited by the Second Research Department of the Division of Investigation and Research of Fisheries Agency of Japan. (3) Off-Shore Dragnet Fisheries, by Shinji ENDO of Fisheries 1110 Agency of Japan. (4) Current Status and Problems in Hamachi Culture Enterprise Developed Around the Seto Inland Sea, by Fumio MATSUO, Katsutoshi YASHIRO and Manzo TACHIBANA of the Office of Fisheries Administration and Adjustment of the Seto Inland Sea. (5) Reclamation of Oita Coastal Industrial Zone and the Policy of Trade Change of the Fishermen involved by Majime TAKAKA of Fisheries Section of Oita Prefectural Government. (6) Routes to Development of Recreation Fishing, by Kashun YASHIRO. (7) International Law of Conservation of Tuna Resources in the

Atlantic CGean, by YUO of Fisheries 4.ency of

11, Japan. (8) Present Status of Forecasting Fish Catches and Conditions of Sea, by Toshio YASUEDA of Fisheries Agency of Japan, - 239 -

(9) Conservation and Management of the Fisheries Resources • of Tokai in the Northern Atlantic Ocean, by Fukuzo NAGASAKI District Fisheries Research Institute. - (10) A study on Compensation for Damages of Fisheries Industries Caused by Pollution, by Yoshihiro NOMURA of Tokyo Municipal Univ., Takayoshi ITO of Shiga University, Minoru KIMURA of Tokyo University of Education and Katsuyuki MIYAGAWA of Research Institute of Citizen's Life.

• - 240 -

Fisheries Multiplication and Cultivation Series 4 Theory and Practice of Lei Culture (Revised and Enlarged Edition) Published: March 20, 1970 Publisher: Corporation Aggregate, Japanese Association of Protection of Marine Resources (Nippon Suisan Shigen Hogo Kyokai) Zenkoku Choson Kaikan Hall, 6th Floor, l-11-35 1 Pa„2:atacho l Chiyoda-ku, Tokyo.

Prepared by Ishizaki Pub. Co., Surugadai, Kanda, Tokyo

•

•

Wer,11,,f- • MM'71

XIONL • 241

22

20 - tiOtal Ç.roduction 181.. - . CU. n jet - na ura 16

14

12

10

• 8

61- 4 ...... 2

or III , 1111111 I11 111, 1 3 5 7 9 11 13 I 3 5 7 9 II 13 15 17 19 21 23 25 27 29 31 33 35 37 38 39 40 41 42 r year . -I- , . . ..i'.). - tb ..o MD ' C\1 - VD Crl - ...- . 1-r ' , \O ' H • 'C\I 0\ '0 \ - 0 \ C>+ 0 \ H i--I H H H ei g .1 HAnnUa1 Eel Production in Japan

Table 1 *World Eel Hauls 0.'000t ton FAO staticS 1 681 •- - 1938 19-181 9 aot1 19. 6 'f9 19611 ' 1 196-11.96311964196D n1 1 • ' ; ' ..' ! . COUNTRY -. - 1966:196fi 1 .-19 1,68 • -- 1 . t • ■ i natural 3.2 2.8 2.9 3.4 3.1 2.7T 2. 8 3. 8 ' 2. 81 3 9' 3 I 1 1 1 1 1 1 --. . ' japan cultured 7.2 0.2 6.3: 6.1 8.1 7. 6 9. 91 13. 4 16. 0 17. 0 19. 6 '23. 6 10.4 0.2 9.1 .q . 0 IL S 10. 7112. 6 16. 1 lb. 8. 11 b, :_..,. 8 -6. 7 L total , USA 0 6 0.9 0.6 0. 4 0.4 0, 31 0.4! 0. 5 : 0. 7 0.6! 0.6! Canada: • 1.0 0. 2 0.61 0.5 0. 6' 0.61 0.7j 0.81 0.8 0;71 0.8 0.9 Morocco , _ o.31 o. 31 0.3' 0.31. 0 3 - 0.3' 0. 3: 0.3 3.6 4.2 3. 3 4.7 3.9 39! 4.0! 3. 3 3.2 Denmark ------1 1 France- _--- 1.0 1.0 0.1 1. 1.41 1. 4 1.41 1.5 1.7 L 1 2.0! 2.6 Urastest n%..v ,...rmany ...1 ... 1.61 i 1.41 1. 1 1. 31 (« 0.51 -- 2. 6 0. 1 0. 4 0. 4 0.5 0.4 0.5 0.1 0.4 0.6: 0.6 Ireland 1 0.1 0.2 0. '..;1 1.3 o.1 0. 11 O. 11 0.1! 0.2 0.1 0.1 0.2

. ItalY - . 2. 8 4. 2.5 2.7 3.9 3.5 4.0 3.F 3.2 3.1 3.1 3.2 ` HO 12..c,lid. ' 2.9 5.01 2.9 :3.0 2. 5 1.6 1. 9; 2.41 2.7 2. 81 3.11 2.7 . yoryray . ______-_-__..._ 0.51, 0.31 o. 0. 41 0. 51 0. 4,1 0. 5.' 0. 4' 0.5r 0. :),- 0.5! 0.6 ' Poland ---f------•- 0.11 o.& 1.2 0.11 0,9 1.01 1.6 1.11 0.9 1.01 1.11 1.1 S pain _ ..___ _ 0.4j 0.l 0. 6 0.5 1.1 1.6 L9 2.3 1.7 L7 L6 1.5 Sued en • 1.9; 1. 9- 1. 8: 1.51 n. 1 1. (9- 1 1 2. 11' ''- .3'. 1 '‘;" 1• i"l. ' I C )!1 1 '7 Eritain ... o.3. 0.: 0.5 0.8 0. 7; 0. 7.1 0. 7, 0.1, 0. :N. 1. 0: 0. 6 0, 6 ___1_ I_ ; -.1 0. 3 0. :I 0. 3 O. 4 O. 4 (9. 4 ' 0.2 0.1 0.1 0.2 0.2 0. 2 0.3 0.6 0.9 0,1 , . - 0.0 0.0 0.1 II. 1 0. 1 (. 1 (9.2 Arti11 tra .1- .-1_0.: • • - -- . - i - - (). 1 0, i i', ,..'. 0. 1 . 0.1 Ëew Zea:lard- ; 1 . • (1, .1'. 41. I 1).'. ,•• ••• ••• Ind. one s 1 -a' - • ... 7 -1 1. 0 -10. 0 31.01 .1. lb ;0,44 ti.„ l'.. „ .1, „ • .TOTAL - - -:•------2.L 1) :::-.: -.4 7

•■• - 242 -

14 ti

1-D •

-94

Mg. 2 Long Dorsal Fin (upper) Short Dorsal Fin (loNer)

Zu • 60' 90 120' 130' 130' 150• 120' 90 6 30' Fig. 3 World DistribUtion of Various Species of Eels A. australis austral', A. n. n A. nebulosa nebulosa A. j A. jaPonica A. o A. obscura A. a. a A. anstralis ubtniiiti A. h. b A. bicolar birolar A. ma••••-1. marmorata A. in •••A. interioria A. a. s A. rostrata A. mo A. mossambica A. c A. celebesensis A. me A. mcgastoma A. ro angailla A. r.. 1 A. nebulosa labiata A. b. p".4. bicolar Pacifica A. re •••A. reihardti A. an .A. .1. Lo ...... A. bornecnsis A. an —A. ancestralis A. d A. dieffenacitt - 24 3 -

Ja»van ■ 177 e' r

f / ,..•.. I 49-n p.' 92 ...•---..... , 7J-,2( -_ „ Pr ;IJ -• °:-1-1.,),t‘-',-..--....7.-- ,- c•,...,/i1Ci.11 /.... • • I / \ b 0 -- --- ■ -7=-1 - - e 1 ,/ \ 1% ■ 01 1 i " 1 ---, // -r - /-"/ // /». /..-,115-. 1 1 ,...,..: ...s...-- 30. 1- •:.3 ,.... / ,,,, .!".... \ ...../ / ‘....,...././...-;...... D., .../.. ,.;),1 •- ■ . '• - - -, , " ----1 Okinawa „...."---,--,-...,2,0_.A.;.% ;..7>e - • % .2' - ';7,,us t ... tslit S• 1----1-N--- Iwojima e'. - - I I i- . './ - e , \ , •• 25. .te,e;-' .:- :-.>-.';n )' ''-' ---,&=, / i '1,41eAlfri /' +r"e4 .//,',/i/ • ..• ' O / w ...... ,...N.Nr..+ ..... I I\2:.{.412:%.> • ‘ • ••• .--'' • • •, "›,,S.Xese , . • .... -, ... ".. .., '' I l • 1 / ‘ \ I ■ PhillPPin2 ,e19el' ` .' •••• " • % •-• ‘,. • 145 * lug. 4 Spawning Ground of Japanese Eel where descending eels were hauled ; where leptocephali were collected o; possible spawning ground ; likely spawning ground o *Translator's Note: Only a few names were typed in. The 145 longitude is approximate.

Table 2 Average Body Length at Ascending Season (unit; mm) Yoshida-town Fishing Port

r.aranra - county Kaisaka-town Shizuoka-prefecture Hamana-county Shizuoka-prefecture variation variation 1 average average

L f month day month day ' 1 /I 22 n 55. 2-62. i 5. 766 -4 0. LI 2 12112:111 51. 7-61.5 511. 612±0. 255 2 11 5 II 52.1 -61. '• 690:.': 6. 116 . I )1 inn 53. 2 - 53. 1 :21. 725 J.: 0. 22;2 3 111S 11 *1 III 52. 0 1 56. 1,80.1:0. 182. 2 31 8 H 52. 5-52. 0 W.609-10.266 411111. -FIl III 51.1-61.7 96. 720 +0. 166 3 )11311 51.7-41.7 56.715±0.222 - 244 - Kg haui

7. 4- 0 Pig. 5 Periodicity of Shirasu- Ce.4 eel Haul near Rome, Italy 1-- (Champee*) 5, NO

I. *transleterated

it-41 I , — -

2. 0

1 , 000

--,

o year

, - /1\1\ .. â 11 i t.> g ,.. Eu,,,,.... , ..,..1, I f3/Aj 0.10 ..,.\ . - I v IY\ f. l■ ■ 0.05 . „ \,/ -'1 i i \ i1/4 I \ / ,fs'&, V 1\1 '‘‘ 1 -\ 11/4k l■ 1 - f v,i v , Y 0.00 I/ t hu;s:l'y[ \f 0.05 iw•„1„i. -18t 4 , 1910 195 1920 1925 1930 1905 1935 1940 1945 1950 1900 1910 1915 1920 1925 1930 1935 1940

Fig. 6 Relationship between the Haul af.Shirasu-eel and Salt Contents of the Sea Uater 10 Years before the Haul (Brun or Brown*) *transliterated

Head Eel Eel and Narrow - 2115 -

* Fig. 8 De-Velopment of Genital Gland (Brun or Brown)*

1.- lecomes B and C.

A 1 and 2; beginning period •3; , egg cells are formed around. the glPrd wall A 57!iIA 4; monoecispu.-- ,t 5; male testis s, 6; - female ovary . , I" • f. I p e)..t. translitera%ed C ;Jî

• body weigh% Fig. 9

Gwowth of Shirasu-ee1

Q; Mat sui

; Tokuhia Inaba

; Egusa & Oye

; Yanagimoto

- 246 -

Table 3 Growth Limit of Shirasu-eel • ( unit; mm) /I 2 3 1-4 7 8 n m( nth e.A 516 9 1 10 thor i 0.15 53.3 0. 15, 1.4 35.6 f.* ...1 0.15 29.3 r. okuhisa 0.15 17.7 , 0.15 3.8 0.2 9.3 1 4(0 * 0.2 2.4 ' 13.1 anagimoto 0.9 2.6 5.4 10.0 16.3 20.3 21.4 : Y: 1 0.3 naba _.. O. 1 0. 8 2.5 _ 6. 2 10. 3 , 18. 0 _ 26. 1 0. 18 21.85 / atsul U.:t0: • .--4..,. 0.14 0.38 .1;14 2.09 4.5 6.1 8,2 10. 9 1.-2:11:1-.T -30:9- j gusa, Oye

Matsui measured the size of overwintered shirasu-eels cultibayed for one full year. There were 1 eel with 110 g weight, 4,102g; 11,85 - 115 g; 36,85-115 g, and 5,30 - 45 g.

• , •

,.....-- Fig. 10

ia...... , . , ., . Equipment of Capturing, a 1.' • - 1 Pounding, and Transportation of Shirasu -eel 1. A' set of equioments to capture .,., shirasu-eel. The wood box Y ‘".74 ' contains shirasu-eels. • 2. Shirasu-eels in a pound. /44" • • b. ; 3. Transportation basket. 1

• 1

:1 (Hamanako Branch Station) L.1.1

-`7

) i À , i • , 1

. .eue - 247 -

Table 4 Hauls of the Culture Stock in the River Basin of Tonegawa (unit; Kg) sen, hand •-,tool hauling net, , prefecture-__ 1 long-bag nobenawa etc.: total net

Ibaragl 16, 900 65,600 • 82,500 Ciba 9,400 80,600 90,000 total 26,300 146,200 172,500

Table 5 Quantities of the Culture Stock Handles by Traders in the River Basin of Tonegawa

monthly handling quantities (Kg) - ----7 . ,1 2 3•J I A• 151M I 6a 7 8Si 1 9CI 101;1- TT -11717 . _ fatal, .-...olace Lj: Al mil 121 6, 466, 3, 621 3, 700 2,592 3,561 2,2, 423 4231 1, 1, 439 439 1 241241 24, 167 US hi bor1i-t omit 311:. 1 (321 1, 419 2,310 1,547 4204201 I 6,317 Namizaili-town Z L1 g 200 1,1, 72517251 3, 81814, 7, 997 10, 428 10, 3 10 4, 255 8, 003 375 47,137 Tosho-lcwn .Ut [13( 2, 8756, , 7001 6 630 6 709 6 630 4, 660 4, 308 4, 308 3, 850, 4, 3901 2,975 40, 606 Sahara! 1 ' ! :f ei 4,125 5,5, 250, 250,1 8, 500 9, 375 8,750 7,000 4,125 1 3. 50( 2,500 53, 425 Choshi-pity 3.000 5,5, 009 000, 1 5, 5, 500500 (3,000 5,000 4,000 3, 5001 3, 5((0 2,500 38,000 Komiketown 11 4q- 10( 30 400 10010 100 50 50 81 2 4111 1 Iacm Kansu-viillage Ul• 100110, 621 25, 541128, 786.33,. 251.33,' 438 30, 809 18, 95320, 762 8,591 210,852 :total

Table 6 Hauls of the Culture Stock in Ibaragi-Prefecture in 1961 (unit; Kg)

!no. of fishermen engaged: type of in the month I tools haul 4 1 5 6 [ 7 8 9 I

total , Ung-bag-net 36 3, 41 2, 778. 6, 153 32 586 6. 998 1 , hand-hauling net 82 1 3, 559' 3, 5 19 1,2(32 8, 379 I eel sen 89 2001 329 1, 197, 1, 75.4 8211 596 .1, 897; i 1 i sasa-hitashi 60 20() 1, 500 , 2, 829 (5 17 289 5, 465 , bamboo tube 68 70 . 617: 777, 323 .1:1 1, 832: tsutsuL;o _ '32 183 . 11,1 _444 . 409 63 128 1,040 total 1 367 3, 828 3, 488 3, 464 9, 481 5, 13 3 2, 002

• - 248

Table 7 Recent Hauls in Chiba Prefecture • (unit; Kg) [. 1961 1962 1963 s t y t consumed'release to river 9% - 527 - 847.5 within eel culture 562 1,248 -- 3,2101 prefect. 'other L_:17 to ShizuOkâ--- 5, 625 20, 000 3, 750 20, 000 11, 475 3,500 21,750 exported to Alchl 1,875 5,000 1,875 5,000 3,000 Ito others 10,000 -10, 0001 price(yen/Kg) * 2,600 700 3, 200 7001 2,000 2, 000 450 700 4,700 3,000 H12, -000 6,000 6,400 5, 000 1,100 3,000

s; Shirasu-eel t; tenbiri y; yobirt Export in 1963:data not complete for tenbiri. data on yobir5 . expected to eXceed slightly over 21,750 Kg.

* Translator's Note: No explanation on two sets of prices. • Fig. 11 Fishing nets to capture culture 4_15 . x stock eels (original drawings). 1. Shirasu-eel waiting net in the river Tonegawa basin .

!

2 2. Shirasu-eel stretching net . in Chiba prefecture. 3. Long-bag net 3 4. Isari-net of the river Tonegawa basin. ï 5 5.,Tamo-net of Chiba prefecture. 6. Buttai net to capture Shirasu- eel in Shizuoka prefecture. 7. Is2ri-net (Shizuoka preeecture) •

Fir:. 12 Structure of the Digestive Organs (original drawings) 1 1. anterior view 2. posterior view 1. details k , cystic duct A. air bladder AD. air bladder duct D. duodenum G. call bladder Et. heart 1. intestine L. liver O. oesophagus P. pancreas S. stomach SP. spleen

PH PH 2 3 4 5 4 6 8

N A 77'"\c. S t omach 2 - x21,7( 0" V‘i, \ ble \x. lu - Ho '

so ■ e 20 40 GO Oc 20 30 40 50 °C temp. - • pH pH 5 6 7 8 6 7 8 i 1 a t r E X v \ P"' .7-i -X.-- ., ..--/ X ...... x o 2 /o7K Q\ H ...... --, t...) • C4 "-i 0/0 • intestines ,1: ,...1 :.; / gi i- U I -i . ri tv . , . Li C )) 4) 5D'C Ul 40 60 80°C ,-, O

11 1- elationshill betueen Digestive Enzymes and Temperature-rE • stomacsh rensire B. •Pancreas trypsine C. liver-pancreas - _ I', t ne ri-r.tez:3 se

- 250 - • 100 fish -*-m A M Inectrt- - •. 410 _1._LUF- Ca o..- xxrucx Orustacea so- \. / X \ • . 4., e •/. \4 ,--0. N. / ,-' - ,ie \\< e' • , -, ....,,. /,•• • ,p,..e.- ,,x, '1 ,•.. 1 'N4: . 9(1-15) 9(15-30) 10(1-15) 10(16-30) 8 (15-31)• month(days)

liff //p rat'( 1)11A\M\ , Fig. 15 Seasonal change of natural food for eels Fig. 14 Relationshir between eyes. and olfactory organs •

Table 8. Consumpti on of different kinds of feed

(unit; ton) _ rtificial • _ eed etc. n- i13-1 1 1 lal I e I a 'total' w Ifp sd 211 14, 78-.11/ 14, 7691 7, 500 15. "431 .5", 298! 1, 8131, 68 15 1960 i 1 II 1 1, 209 101 1-1, 950 18, 795 9, 118 26, 3791 69, 2.13 2, 429, 25 16 ; ■ 1962 41 51 8.178 38, 2911 2,051 12. 0121 60, 53.21 609, 0 4 0 11 17,023 "5 631 3, 1ri1 33.0.10;8 78, 50' 7871 12 678 _1963 1 ' ' 1 - -- - 1 - ! 1 01. 23, 297, 37, 2651 2.389. -15, 327108, 280, h 4091 0- 403, 28 1964. I _! .196 5i 1Y. 10, 827; 16, (102, 6, 306 . 68, 5301 101, 666, 01 1,021 4,912

01 61 6 399• • - 1 19• '1(*•• )11-1 8 0- 11 11 fir"' 78 .1"• it 9 1 dI "918%). • 36C) 196 1 O 6. 3, 397 9, 565' 24, 58.1 1 37, 909 d 528,268 1967 1 . 1 3631 1 1 1 1

fi; fresh larvae dl; driod lar7ac 1; leckineton m; macIzorel s; sardine o; others • w; fish ;;aste fp; -nowder. and residue of extract 251 - t n e l_ 1 ic ff e co

ti

4-1 100 200 3101 1 4:00 5110 600 dys pe.e.eq4.4g.

Fig. 16 A group of eels Fig. 17 Relationship, between at feeding time feed coefficient and feeding days

cri 44:1 0 -P summer c5 Q) 3 N P. F-f x vinter •r-1 c0 • 2 Pi bD 0 in Jo A /V-V r-1 « PI r-1 11:0 100 200 200 400 000 000 700 800 900 wàtt3_12 _06 ‘.20 24 23 32 36 10 .l'ataPeC) (g) ce body weight 4.( 00 • P4,-1 • Z. 1.) / Pig. 18 Relationship 200 between number U.; a) ,summer/ •o 200 wintr of respiration bO and water temp.. • 100 x (original o • G) .1. drawing) 40 ›.4 water temp. o Fig. 19 Relationships between amount of oxygen consumed and water temperature and between body weight and area of gills (original drawing)

- 25? - •

Table 9 Relationshil:, between body weight and amount of oxy,7en consumed

5 10 20 50 100 150 200 300 bOdYITT,Q1'71 -1t (e) OXYgen C 011S11/11:01c/hr) 0.75 1. 2 2.0 3.8 6.2 8.3 10.2 13.5 11 (ceilcg/lir) 150 120 100 76 62 55 51 45

• • Kasahara 8: Nakamura (approz.25' 20 0 San° (WO (1) Sanu C)

tion 0 Takahashi (15 . c) .31 e Van Dam (a02r 01 . 18'C) fEs Gardner & King (25'C) ‘,1 Gardner & King (15'0 4-4 • Egosa (25'C) ;4i 5

consump Pi n e

F-1 Saito (25*C., running water system) Oxyg Q Pi Cbee CI* Saito (25t., standing water system) e Saito (appros.16 .C., running water system) e- Sait0 (approsleC., standing water system) 0.5 Ick5 I I I I I,/ LA LLL 1 1 I 11111 10 1.000 body weip:ht (g )

Fig. 20 Amount of c)::yen consumecland body reight (by Tua) • D E F I bp

0. •-• tt

...

pig. 21 Underground Water

A sea level well spouting seawater seashore (h) self spouting alluvial plain _e_ pipe well terrace d hand-lad ling well fan e. pond-like spring mountain district f. pump well G sea-bed (g) power assisted boundary between sea,-water.h. gathered water in underground and fresh.water 'bucket weIl -pocket rock layer gushing spring underground water level hidden stream 1 mountain stream - 254 -

Table 10 Maximal and minimal amcunts of soluble oxygen in. -A . ater 0 maxl.mum minimun ITobiio .0=1, 7 5-59 Hi'rashi WATANABE 1-1 .12 0.43 TAKII?:A7JA and SUGITA 14.10 0.75 9. 1 8 0.74 Toshi InABA 22.39 o.o6

Fin:. 22 Plantors in an eel cultrre pond 1. liraehianne bàeri. 2. 17, nrcenlens. 3. Il. Para rar. bbirerns. 4. ii. para. 5. B. Plirdtilis. 6. Kern/Ma ralga. 7. K. urenlar. 7. K. rat ea J. must rum, 0. K. xra ! • I , f ■ ica.manal roa. 10. K. ral ea a,: yawl. trim. 11. K. qua! ridentaluç. 12. A'. rat ga herie.z.asynanetrica. 13. K. mehl,•alis. 11. Triarlbra Mal ,v1b.ra re 17. 8 17. T. 17. T. lermiralis. 10. Filinia loarisela. 19. Itoçptina longirnitrii. 20. ". Jot.. lil ,,1113. 21. Cyclo.as rietnus. 22. Paramecium sn• 23 . SI 7P. 24. Pyre:nag/or/tot:a telrarl ynchue. 25, Peraliurn hirundinella. 26. M ridiniunt ;red unense. iç rujnle,,a. ,,1)• ?A. • margi tuna. 30. i'Mia.tium duPic.r• 31. Imnelicus var. su&alsus. 72. 4 nkistradesInus op. 33. Selenaçtrum gracile. Scenerlems. quadricauda. 33. FM4071. 41,7 op. 36. Pandorina op. 37. Pleadurina L'oeystis op. as. Narks, la sp. 40. syn rang op. 41. ().ocilia feria op. 4 2. 21 11 ■ 14(letta SPitindel. 43. Chlarella Pyrenuiclusa. 44. Lyngbya limnelica. 47. Pediastrian Talc :1.1 Eeasonnl veriation of the eel.pond plankton (unit; %)

• summer winter species* sPrirel fall

0. 7 . 0.7 1 1.5 2.9 Zoo ) 1 all gPor-l o a 1.0 1 0.3 Rotatorin 35.9 58.7 71.4 63.2 CoPePoda 12. 0 22.0 10. 2 36.4 Claxl.qcrra 52. 0 15.0 1 18.2 0.6 Phy 99.3 99.3 1 98.5 97.1

{ Myxophccaye 6. 2 86. 3 92. 4 29. 9 Diatomaceac 55.0 10.2 3.2 8.5 ChloroPhyceae 38. 4 3. 5 4.4 61.7

•

Fig. 23 Major zoopinnkters Table 12 Relationship between that appear at the Growth of Mcrocystis changing-water and 01 content of pond water. ther degree of grcuth rphyto- of Microcystis plank- ' 1. Brachionus calyciflorus PALLAS 2. forma amphiceros EHRENBERG ton 3. if. amphiceros EHREN B. 01 4. f. anuraeiformis BREum. Brachionus plicatilis 0. F. content very aver- ;little MOLLER (.o/no) rich rich are little ■■■•■• 0.1-4.0 5 10 3 1. 0 2 7 15 11 3 2. 0 3 6 5 3 1 13 3.0-4.0 1 2 3 4.0-5.0 2 1 1 5 5. 0--6. 0 1 1 3 6. 0 8 7.O-8.0 8

C..tej.1 10 23 26 18 9 51 - 256 -

•

FA

re:1 ïti

■ ■ 1 1 ■ ■ 1 1 0.3 0.4 0.6 0.8 1.0 1.2 1.4 multiplication coefficient (b ) oft: Potifera _ Fig. 24 Curves to be used to estimate the number of days to come before the "Caneirc.;-uater." takes Diace,,basod on te current C.crzity of Ectiferc. inc71_7f.uals (N n ) and their multiplication coefficient -() (by Ito)

abscissa;multiplication ccefficiont ( C) of LotifiDn'a ordinate:nurber of days to come before the "C-haning-uater" • likely occurs ro . 1,5,10,20 sbor number of the Individual- Rctifera by a density unit (per lee). Louer•limit of eac.1.. band correspLnds to 0 inc'ilfiduals/cc. and the u7-rer lfrit to 50 irCivicluals/oc. Thercforo, the number• of days estimated by this figure is barcd or the ep,7 1:lor n tlo re..1;c1 c2..ie rtartr". It is not to estimate the nlength af period by number af days":

Olb Table 11 Lethal concentrations of various chemicals against Branhionus Plicatilis chemicals lethal concentrations 1 note 01«•■• bleaching powder 0.75 — 1.0 PM as effective Cl (effective chlrine) copper sulfate (CuSO4) 2 — L. PPM 0tt04. 51120 calcium hydroxide 200 Mom Ca(01-1) 2 (0a(OH)2): salt water or fresh. 10% (hid). salt) 01 water (salt content) saine 0.5 - 1.0% (low salt) u [ Table 14 Deepness of the bottom mud of eel culture ponds in Kawajiri area and number of Ponds Shallower deeper than than .depth (cm) 1a 1/117 1920 total 3 3 a 1 57 79 9 11111 1313 151 no. of ponds 13 31 24 20 17 6 2 1 4 4 4 125 er centage 10.4 24. 8 19.2 16.0 13.6 4. 8 1.6 1 3.2 3. 2 3.2 100

Table 15 Concentration of Organic Matters in the • pond bottom mud

1Toyohasb± Hamanakol conc. of area 1 area-. 1 total orpunio Inc.. inc. I 'no. 1 matter in lof % 10f.. 'i ,/,`I • !of ,oce bottom mudipond . .â, ondi. <5 (%) 9 : W. 5 12 , 14. 1 . 1 M . 16-2 ; 5-10 15 ! 31. 0 38 41.7 1 53 ! 41.1 i 1015 11 25.0 27 1 31.8 38 1 29.5 >15 . 9 20. 5 8 i . 9. 4 17 1 13.2 . I .

•

- 258 -

Crl Cr\

If1 * c..-%

Fig. 25 Productivity P>a 2 difference between -P • • Yoshida area. (•) and Haman-Tim -P , • area (o) 0 - o 0 o • o 0

00 110 115 n wt. losa by combustion (»)

Table 16 Area of eel culture Ponds in Yoshida district (by Uehara) • aree- m2 I - I -826 826-- 1022- 2611- 396i 5289-- 934 -0256 1-1 1322 ; 264.1 3967 5289 6611 7931 .9256 9917 -t otal

before the 7Tar 1941 number 1 9 •,8 1 71 20 4 4 1 141 or as figured by Matsui /0 •). 8 6..1 19,8 50. 3 11.2 2.8 2.8 0.9 100 (10 52) 1956 number 1 18 1 28 1 58 16 1 1J 0 0 125 . 0.8: 11-1 22.1 16.4: 12.8 3.21 0 0 100 % -- after the Nar number 71959 1 2j 121 7 J 2 0 0 {-5-7 I 3.5 21.0 59.7 12.3 3.5 0 0 100 1962 number_;___ 57 el 80 1171 177 54 9 31 0 ree of 10.6 •• 7.6 14.9 21.7 32.9 10. 0 1 1.7 0.6 o 1 100 * Mot including the culture stock pond which belongs to Marahara Fisheries Multiplication Cultivation Cooperative Association. Only ponds used for cultivating marketable eels are counted. ** Only the number of ronds owned by fishermen who own only one single pond was counted. *** Total eel culture pond area in Yoshida district. Calculated by aerial photo taken by Osaka Airlines Co. Titd. on Sept. 5, 1962. 1/4000. - 259 -

• -4.4- e4444.4,,, -aerm.a.. • - Fig. 26 Various designs J. and structures of • rest areas. 1. Gravels are placed near water inlet. 2. Oigawa Eel Cultivation

r Co. Ltd. : 3. Kawajiri district

1r)

' 14›4.

• "

try • •

•

-,-=-1. -7741: '..'..2-\:4= 1,..44 ,,,,e • • - • .4.: . .. • -.; t w:•r,leeenete "--' I Oki 4. ... './... • , .-,

y •

; • .

F . P: *: 4 •

. . 4.14.44

Fig. 27 Water stirrer 1. Water stirrer in adult eel culture pond. 2. Twin stirrer in a. shirasu-eel culture Pond. 3. Under oreration. L. Stirrer orerated while fresh water being Poured in.

. . • • .1 • • ' • '41 ' ' • - r : •.

•

FiP:. 28 Arteisian uell af Fig. 29 Shallow well Oigawa Eel Cultivation of Yamakawa Rel Co. Ltd. Cultivation Co. Ltd . in Kagoshima Prefecture.

. , ....,.,.. .. , . •.. - ..., t : -,•-••,.., . ,,... r.,...-: ,:,-;.7..14.,:.`', ',....:, :::,_ ..-.....-...... *,.. 4 ".•.'..'.. - ...-e.,••-e : '.e.t.".,1 F :-...... A .: ,. . . ,...0.

. t . •.•—„..i.,• -.:...e,.,- d_;....., ."::t - ";* t ' . . ,i';.- • ,. I... r ‘•,;.;!. 1:1'm ••" •: - '.. • ' - • ' , ,t . '.--„,.. :•• .„ ..,...z,„..-;,:„..... ; 1 . 1, T ,:,....„ i';:.-:.,,,t, ï •....., : T . ; ^ i. . 4 '). 1 . ..1›,,;. • i. \:•,r, R ',;(e.',. -• r -1. it!' . .... N •-• 4 . • 44 '.,.' .. t... „ 4" ■ .`• •• ., p 111 ti

,

"*.t. t

..fe•-•'..11„›..,41 J1 i - • : - - • - - • . • •t, ; :•••••. • ;.S ^. 1 • '•1' • •;" ■•• •

• ••• • • • . •••, 1 ' • » ,..r • ■./1 • • • • \ • • ' — - ••;. : , • . • •

, .,.,,„....„ r.g:••__ • à r,,,,,, ,,„ , • • ,.....,,,,,,•...... •._ .".,,•._•••,...._...... ,. • . ''..-• ; .,./•:, 7 t . ' - :1 ; . e „ .4 ' • ....i .•.- -,..."-;..m. : 1 • i , :,.., .. 1 . é1t' P,`,.::9;£.i '-•-• ."'.' ,«-:..- ' « . ",.. - ,....,:f ;• ,7- `. •• % . • : é . ..,',,,' . • .•• • • -. .... • • •.„, •,, . 1 ei ,• - ri.4.'.. ..::.: ...,, ,i: . 1 r•:•- • . . f. . ....-.,-i . ".: , ,.1,•,,,,,! ; . 1`. • • 2 r..., • -I i'• .' . ' .k F. ., '•1 ■ .7.' . .i..•. ' • ,.... , .,..• • -. ,•• ; „) it . . ••• :. :. . 1 . • ; . . . . . ' - - • I 5 • Ir• • À e • `

t • •. ' • - • • . • ,

,,• Q.• ;./ • • .‘ . tee • • •• • • -• ; 1e.r.4• r .1- • - , - ' • . . " . , .„ . '. • - .:.• "1: , • ' ■ 1:...;•; , ,,,.. .'-.: , ..:, , ■ 1. - ...,.. ••• -.% ' . . • . : .• ‘ • . ,,....••••( '•' , • 55 '• .‘ •• 5 • • • . ._...15:+5•- • »2› : • • ' .. J • l. • • - . • " ..‘'' 1.. .1 ' . ' 5

.,, / ; N'...... ',....›'`': ' ;%.• .••■.:;:-‘ .. _ •i: — - • .. ....

Fig. 10 Pond huildi (tiohara) - "D(. 1 -

Pig. 12 Metamorphoses af Anchor-worm (rasahara) 1. naupltus 2. metanauplius 3. co1)e-Do:1d 4. after copulation and before enterring into eel muscle 5. immediately before- entering into eel • muscle Fig. 31 6. immediately after entering into eel Anchor-worm mescle 7.- spawning stage

Table 17 Metamorphosis of Anchor-worm

213 I 4 5 note 1;cdy length (mm) Œu 0. 53 0.69 0. 83 1. 10-.1. 29 In the 5th period, 1st antennn 2 2-3 4 4 4 male and female are 2nd antenna 2 2-3 3 3 3 differentiated and thorax 3 4 4 4 4 . they copulate. abdomen 1 I 2 3 After that, male dies swimming legs 1-2 1-4 1-5 1-6 1-6 and the female under- genital organ .1 - yes yes well I goes further develoiDeà phosis. 'formszorms its body csrld t and enters into an eel t s body. Table 18 'Relationship between temperature and number of days of cultivation (untt;aayl

average water temp.0 321 30 1 28 26 1 24 22 1 20 1 18 1 16 14 hatching stage 0. 1. 1 1.3 1. 51 1.7 2. 01 2.4 2.8 3,31 3.8 91 1 lst copeppid stage 1.6 1.9 2.3 2.8 3.4 4.1 5. ( 6. 11 7.4 9,0 5th corepoid stage 5.1 6. 2 7.5 9.0 10.9 13. 11 15.i 23.1 27.9 1 19.11 female at metamorrh.. 7. 4 9. 1 11. 1 13. d 16. 5 20. 1 1 24 5' 10 0' 36.5 4.1.6 1

Table 19 Survival rate of anchor-worm larvae in dilute sea water dayb -01 conc • o/on 1 2 3 4 5 6 7 8 o/oo fresh wate .0 e4z. 100 97. 4 97. 4 96. 2 9.1. 8 94.8 94. 8 91.4 • 1.0 100 100 100 100 92,9 92.9 85.7 85.7 2. 0 93.8 93. 8 93. 8 93, 8 93. 8 93. 8 87. 5 87. 5 3.0 100 100 98.3 98. 3 95.0 95.0 91. 3 91. 3 4.0 100 96.7 85.0 79. 0 76. 3 68. 0 49. 3 39. 0 5.0 95.7 72. 1 48. 0 42. 0 32. 3 20. 3 7. 7 2. 7 6.0 100 71.0 54.3 • 12.3 5.7 0 0 0 7.0 100 44. 4 22. 2 5.6 5.6 0 0 0 8.0 , 88.2 11.8 0 0. ..0 - 0 0 0 water_temp.; 17,3.-1_22.8 00

x 3.3 2 perchlorine Kg

8 1 2 1 1 0 2) 2 4 6 8 0 2 4

4,500

4,000

3,500

3,060 , • m 2 500 i\ .8.000 10 kg 20 40 50 60 70 80 90 m bleaching «Powder Fig. 33 Amounts of bleaching powder and perchlorine required to exterminate anchor-worms (relative to the area and depth,of rond) * Translator's Uote: -,There are 14 x 2 Ohlnese characters in the graph. They.are all identical and mean water depth (in cm). - 263 -

Table 20 Survival rate and activity of anchor-worm larvae in dipterex solutiow.7

_survival. rate c:t" rate of. conc. _ anchor-worm.(%)successful after after after after metamorphosis 24 hr 48 hr 72 hr 120 hrto 1st • / conn -hoid contre '. (0 08.1 i 97.7 91.0 i 89.9 88.9 0.1)5 05.0 91.5 91.5 90. 5 90. 5 0.1 41.3 22.5 • 21.0 15.7 13.5 0.2 12.0 3.8 0.2 0.5 4.2 0 LO

Table 21 Rafety concentrations* of various apreicultural chemicalsainst agricultural fish safety conc. cEemicals pum. parathion ;eel, carp, crucian carpi gold fish, killifishi a 2-0. 4 chlorthion 'eel,_killifish . , 0. 03-.4/. 17 tcruthione**, carp, crucia, carp, iciliiiisn malathowr** . ic:arp, crucian carp,_ killifish 0.3-1. 3 enctrin 'carp, crucian carp, killifish am-aom T.E.P.(T.E.P.P.) carp, crucian carp, killifish a 2--,0. 7 diazinon 'car Pi crucian carp -, killifish 0.3-a 4 aipzerex leel, carp, cruciau carp, lialu.lïish . __ „ . , _ . . _ _1 6--7. 9 * TLm (96 hr) x 1/10 . • **Translator's IJote: The author uses a word e guthathione or gusathione* - which this translator cannot find in various - handbooks and indexes. Accordingly, the chemical sounds close to it, assuming a misprint, is typed in the table.

- **Translator's liote: lualathion is the more widely accepted name.

et,

2ig. 34 Pathogenic organism of 'fin-red disease' by electron microscope),(Hosbina) • Paracolobactrum anguillimortiferum Hosblna '62

• N

- r .e'eïe: I I

V.' 5"-- • *

• .J41,

( 7/ to*. • 'III\ II '1 • /74 " 1 sr — 2V-•%'' . / t

Yi, , 735 Wàtem-rungus disease Pr d its pathcŒen (Hoshira) nung hyphae of Saprolegnia Darasitica

. A

'

• • e; , ,4 • • I • 4.e. .

î

•

:erg. T36 Aïr-bubble disease of shiratm-eel u1or.lh1na)

• . - 265 -

Table 22 Characteristics of Each Parasite Myxidlum M. Lentospore . L. .anguillae matsuii ermatobia 7 anguillge sporangium Iformed in formed in buried deep in several of them •connective connective connective . . scattered in tissues, tissues, tissues, 0.14 connective tiss- !1.2 x 2.0 mm 0.79 x 0.41 2.76 mm. ues. not agglu- tinated. 0.8 x ; large. mm large. circular or attached to oval. irregular. 0.7 mm. mainly outside skin attached main- on back of of host. ly to outside host. skin of host. spore spindle-like, oval or x 5 pL. 8 x 9». thin straight or spindle and thick wdll membrane, surface twisted straight. with several flat and smooth. slightly in 12 x 13p.. wedge-like several short S-shape. 9 large. ' promontories wedge-like pro- x 2.8)›.1arge. near rear montories at rear : 22 fine end edge. edge. thin membr- stripes on round. side ane connecting surface, view like them extends terminal ends, convex lens. slightly towards piercing out front. of shell. (4 Pplocyte 2. each 5 3.5 5p' long. . )Ji. always at both front and rear ends. polar thread long and fine. 251.4 . length un- 28)e. known. growth of starts to same spores_in multiply on sPPrangium inside wall of sporangium and pile up towards centre, centrally situated spores. maturing faster. enlarged sporan- • gium breaks down expelling sporos to out- side of sporan- glum.

- 266 -

Table 23 Kind of parasites and their parasitic ratio

par. sitic para- ratio sitic [Plistaphorai MyxicliamMyxealteNerawa- p+ ',A- myx organ ratio Sp. sp. sp. clasp. i Illy Myx +My muscle 53 45 6 4 2 kidney 74 28 48 13 7 1 4 spleen 25 15 3 1 3 1 gall bladder 30 11 15 1 5 3 liver 21 16 4 1 1 intestines 40 12 10 13 9 1 1 1 air bladder 32 32

• '

,

, CM 0 .5 i. f 1--1...... 1..—t—L-1 ...... , r.,. .'-, . • . e .' ‘'..7‘ 3 ..—.... • : ..e , I. ,.. ' 1„ ., „',.. ,,,L . p' e' e,..■ 1:-...„ ' ,i. ., , ià et; 4,4. e,., . : .....:- '.:.` .'!....„°.•'D el....,..::::,;:„. 5:.,....;:r> ''. ... *.>4 ' -‘...'..? ":e• •'. e' . fa s ■ - s . :f r 1« ';'4 ' . ..z. . r ' „ Da, , - . • 4, S...... '.7.41.1 I.:, ;;Y:,,,, ,*••• ,e ,.,1,, es, -...,„, ,,,!,,,:• 1 '',. ....,..) e....,,,,••;;; y,.:•.' ..,. ..1.«.•.' .. ell • ; •.: e.,. ..i. ''4 . • ...,.. 4., '‘,., '"*"; 4, -i . , e-...,- ' : ' ,,,

. ; density of cultivation , I' -:. `.1 4 • , , "-. ... s:4 . à " _ • ‘m. 1r • ' ' t. ' 11g. 38 _ ,,....r RI ..id.. , ...... %ib1,,..—.1A...... - ' r . ...1 lielationship between density2 Of cultivation (3.75 g/3.3 m )* and weight increase ratio :01g. 37- .èiuscular necrosis (Hoshina) ulceration of muscles and the lower photo *Translator's rotes is one of the patho- There seems to some error. genic organisms, In comParison with Table 24, rlistophora il.11 ,11.111um. .the unit of abscissa should be a g/3.75/3.3 ni) - 267 -

l'able 24 Relationship be -bweon density of eels in a- . pond and uelf:h-t, increase ratio

density or . . ' I tin '• iss I 3no 1 375 I 430 ....,—....—.....— re...U..1:USSLti_ On weight i.norease ratio • 1. 20 1 0.82 I 0.89 I 0.63 i 0.80 I 0.49

Pig. 39 Ani-zashi• (or Amisashil 1. ..")coop, up eels gathering at the feeding post with a net. 2. Eels hauled are graded irnmedia-,tely.

•i; 1

• • . t11\ ..1 , t ei I , 1•\ -1•

• f

, • •

, . 2

. • n • 1 h.. ,.• , .'

i '•

• .

3

40 And-biki or ranihiki) 1. Ami-biki- under operation. 2. Bull .the net towards sLallciererds cf the iz.,: crd. Prerare a pcund in the pond with a net, and place the hauled eels in it and grade the,n-i. L. Suppl:v- f:resh wate -r conmtantly so as t • p.:Nro-ld "ana'-'aree ft . ( rir 'e T'F-.-t '3 rhotns by T.Telia-rel) - 268 -

Fig. 41 winter haul and Pond refresheni ng

Table 25 Degree of size variation of eels_ cultivated_ under the sanie conditions A width of variation. L 7 I 9. 19. 0111 I ,4 average body length.. -L '''"e I 13.7"'-' 11 om standard deviati van l ati on c oeffici ent 15' 76 11(1 ±°. 7:1 9. 81±0.47

e- 42 Grading 1,2. Gradin g at summer haul by.ami-biki method .. • " .s (in pond) 1 3: aradin g at winter haul and pond refreshening - t (oh grading bench) (Photos 2,3 by Uehara) 1 z

3 - 269 -

Pig. 43 Disinfection of pond bottnm by spraying lime at rond refreshening

1.././/////////////1//////////////1 (C) (L) (K)

Figs. 44 Tunnel Model of eel culture rond (Tto)

.water InIet tank locle B. drainage tank K. drain pire 14 drain ditch C. tunnel pire

iron drain drai plate /

drain tration.

room. culture pond -1 j rate'r 4ter rreciritation inlet distribution ditch tank

Fig. 45 Circulatory eel culture pond

- 270 - Table 26 Loss of weight of eels during i Tkishime t tl-eatmnnt

X )([ m month._____4. 25.0°G-34.0°C avc-nrc 11.6°C-17.9°C 8.6°G-15.2 °C 3.0°G-10.6°C water temp. 1 . . . 1 2 3 . 4 5•• 1 2 3 45 6 7 8 b ; month/day a b. . ,‘ . 0 . ,m2d a- 711/19 3 3.60 3.39 1.87 3.13 2.17 2.91 0.933 X127 5 5.18 3.97 4.07 4.02 3.83 4.15 3.92 3.55 4.08 0.816 711/24 8 4.96 5.23 3.62 3.42 4.12 4.27 0.291 XII 1 10 5.81 5.39 5.01 4.68 4.81 5.03 6.03 4.89 5.21 0.226 711/29 13 7.13 6.15 6.87 4.30 5.19 5.93 0.313 XI/ 6 15 7.14 6.30 6.53 7.23 6.80 6.81 8.44 6.95 7.06 0.310 S111/ 8 23 7.85 8.51 10.55 7.49 8.65 8.61 0.260 X1/11 20 0.18 7.79 7.00 7.36 7.81 7.03 9.04 7.81 7.73 0.141 W/18 33 9.31 9.62 13.30 8.95 10.16 10.27 0.165 X1121 30 10.13 7.95 7.80 7.63 9.15 7.70 10.54 9.15 8.76 0.093 70 /28 43 13.78 13.16 17.32 12.02 13.70 13.98 0.311 MP 1 40 11.04 9.13 8.27 9.10 11.44 9.81 13.32 9.62 10.11 0.133 .t 1X/ 9 55 14.57 16.08 18.72 12.72 17.06 15.83 0.155 Mill so 11.55 9.901 9.00 10.37 12.65 9.03 11.16 11.52 11.07 0.093 a; number of days elapsed b; average loss rate e; average daily loss rate

watez 10 Fie:. /46 ,Chatga of' body composition during Ukisbime t treatment 10 dried matte

CO -Cl) her 0 10 r-1 solubles

. . total It • " Iv 10 -P . cd .--• m 1.0 U1 •„ 0 - 8-i • 1. 0.6 - • summer .14 x winter. çd • . nzt 0.2

- . Ci Fi 10 • • sunrLler winter 10 20 30 40 à 6'0 days number of days of tikishime t treatment - 271 -

1. . '7,, 1- • „ • -

•

/ • i. / •

/ . 41 )',. '....e.--e•\,:. 1..e,?.' '.''. .,.... 1.1.il .'''.: ." ;

.e• . , L".. ' 1,4›,.,..b..\,...... Iste•:'. ,,.,!.• ,..

exe.

'"4111

) ,4W4,

Fig. 47 'Ikishime r operation by Elarahara Eel Ouitaral :Fisheries Cooperative Association 1. View from the site of I 1kisnime 1 operation. Water sprayer can be seau at the centre ()J tue pand. 2. Grading and preparation for shipping taking place after 'ikishime'. J. uels already-placeu jja a, wooden shipping oox are kept in water waiti.ug 1 or trailsportation. .4. Gradin anU weighing.. Fig. 48 t Ikishime t and Packaging

1. t Ikishime l room. Water is showered to baskets piled -up from the top. 2. A container made of synthetic resin and used by Hamanako Eel Cultural Cooperative Association. It has a long and narrow slit on the side near the bottom. 3. Cooperative f ikishime r treatment of Narahara Eel Cultural Fisheries Cooperative.Association. After weighing, transferring eels into a wooden box for transportation. 4. Ice cubes are being placed in each bamboo basket, when a basket is to be used for transportation. 5. Ready to be shipped in a basket. 6. Eels are placed in a polyethylene bag. Two of the bags are placed in a cardboard box and packaged. (Photos 1,4, and 5 by Uehara)