In Body Size, Brood Size and of a Freshwater Shrimp

Jap. J. Limnol. 41, 4, 185-202, 1980 .

Geographical Variations in Body Size, Brood Size and Egg Size

of a Freshwater Shrimp, Palaemon paucidens DE HAAN,

with Some Discussion on Brood Habit*,**

Machiko NISHINO

Abstract

The variations in body size, egg size and brood size of berried females among populations have not been known in Palaemon paucidens. These were examined among 28 local populations from various inland waters over its range of geographical distribution. Body size differs among the populations. Egg size is almost constant regardless of body size within a population, but differs among the populations, and the largest from Lake Akan is about seven times as large as the smallest from Lake Biwa. Brood size increases with body size, however, relative brood size is almost similar within a population. Among the populations, mean brood size and mean relative brood size vary, but fall within a limited range, except for the mean relative brood size in Lake Biwa, which is exceptionally large. Relative brood weight is almost similar in a population, as well as mean relative brood weight among the populations. Thus, mean relative brood size is almost inversely proportional to mean egg size. A geographical trend is noticeable in the variations of these two values (i. e., larger mean egg size and smaller mean relative brood size in colder waters), except for the populations in Lake Biwa and two rivers of Boso. The small body size of the population in Lake Biwa can be related to its life history, in which a longer period is spent in colder conditions, and the high relative brood size can be regarded as its adaptive strategy of allocation.

described by YOKOYA (1931) from a pond 1. Introduction in Tokyo, besides the apparently smaller Palaemon paucidens DE HAAN is a sizes of their eggs in comparison with that common freshwater shrimp in Japan, dis- from other localities. tributed widely from Yaku Is. to Hokkai- It has been already recognized by KUBO do, as well as in Sakhalin, Etorofu Is., (1942) that there are two groups of species and Korean Peninsula to the north (RATH- of the genus Leander (=Palaemon) in BUN, 1902; KUBO, 1942; SHOKITA, 1975). Japan and adjacent areas that differ in egg It inhabits various kinds of inland waters, size, and Palaemon paucidens belongs to the group of large egg size. KAMITA from small ponds to large deep lakes and from the mouth to the upper course of (1961) extends KUBO's finding over the rivers. During the course of the study on Japanese freshwater shrimps through his the life history of this species in Lake extensive survey, and indicates that the Biwa, I noticed that the newly hatched eggs of the present species are larger than zoeae released by the females from this those of any other palaemonid and atyid shrimps in Japan, although this place has population were much smaller than that been taken over by Macrobrachium shoki- * Contributions from the Otsu Hydrobiological Station, Kyoto University, No.264 (Foreign Language Series). tai (SHOKITA, 1973a). KAMITA regards •* This study was partly supported by the Science this attribute of Palaemon paucidens as Research Fund from the Ministry of Education, "Paleolimnology of Lake Biwa" . that which made itself possible to be dis- 186 Geographical Variations of a Freshwater Shrimp tributed further north. He also states that the number of eggs carried by a female is closely related to the size of the mother shrimp, but he denies the geographical variation in egg size or in egg number for Palaemon paucidens. These parts of his statement are, however, confusingly cited by SHOKITA (1975) and TATSUKAWA (1977) as that the females of northern populations tend to bear larger eggs than southern ones in Palaemon paucidens. On the contrary, KAMITA, in the same paper, refers to the apparent variation in size of the eggs of Paratya compressa. Nevertheless, little attention has been paid to the variations in the size and number of eggs within a population or among local populations Fig. 1. Map showing the localities of the materials examined. The numbers of of freshwater shrimps and prawns. the localities are identical to those of Table In the present study, the results of ex- 1., as well as in other text-figures. No. amination of the size and number of the 27 is Syananuma pond and No. 28 is eggs carried by a female among different Lake Tibesan. Symbols mean oligo- trophic lakes (○), eutrophic or bog populations of Palaemon paucidens are lakes (◎), ponds (●), middle or upper presented and analysed. The geographical courses of rivers (＋), and river variations in these features and their mouth (-). meaning are discussed from the viewpoint of adaptive significance for sustaining the Ten eggs, which were apparently not population. artificially injured, shrunk or bursting on 2. Materials and Methods hatching, were removed from each female, and their lengths and widths were meas- Berried females were collected from vari- ured under a stereoscopic microscope to the ous inland waters in Japan to cover the nearest O.01 mm. The body length of each range of the geographical distribution of mother shrimp was also measured to the the species, as well as the range of its nearest O.1 mm (from the base of eye to habitat, during their breeding seasons from the tip of telson) , and the wet weight with 1974 to 1978. All specimens caught were and without eggs were obtained to the preserved in 10 % formalin, except some nearest O.001 g. The total weight of eggs of those from a pond in Aomori Prefecture, carried by a shrimp was calculated from which were preserved in 70 % alcohol. the latter two values. At the same time, The specimens collected by Prof. D. the number of eggs carried by a female MIYADI in Lake Tibesan of Sakhalin and was counted. Measurements were made of Syananuma pond of Etorofu Is. in 1934, all of the above characters for all berried and retained at the Otsu Hydrobiological females when the specimens were rela- Station, were also examined. The localities tively few, or for 30-40 individuals; body and dates of collection of the specimens length, however, was measured on all examined are given in Fig. 1 and Table 1. berried females only when a large number NISHINO 187

of specimens were available. Only the body (No. 22), in which the distribution is bi- length and number of eggs can be consid- modal and the larger portion consists of 2/3 ered reliable in the following treatments of the females. The berried females from for specimens from Lake Tibesan and Hokkaido, except for the small females in Syananuma pond. On the contrary, the Lake Ohnuma (No. 22*), are larger, and egg size is considered reliable for these those of Lake Biwa (No. 1), Mandai-ike localities (No. 2, 5, 6, 18, 20 and 23), since (No. 4), and a pond of Aomori (No. 16), very few specimens were available. The are significantly smaller than the others. measurements were mostly done from The body length of the berried females three months to a year after collection. mostly exceeds 3 cm. The smallest berried As is generally admitted, it was quite female recorded during the present study difficult to properly remove excess water (2.42 cm) is from Lake Biwa (No. 1) ; it from the individual berried shrimps to is much smaller than the 3.1 cm reported insure equal wetness at weighing. Conse- by KAMITA from a moat in Nara or the quently, it was almost meaningless to 2.9 cm cited by KAMBARA et al. (1967) weigh them with an accuracy greater than from a pond in Kagawa. O.001 g, and inevitably the calculated A definite relationship exists between weight of an egg does not suffice for criti- weight including eggs and length on log cal comparison. On the contrary, the scales in each population, as is indicated length and width can be measured with by the highly significant correlation coef- greater precision for each egg. Thus, the ficient (P<0.01), the slope being nearly calculated egg size permits closer analysis, three in most of the populations, indicating and at the same time enables clarification similar body shape within each population of the variations in egg size with the same (Fig. 4). Covariance analysis shows that mother shrimp. Therefore, the calculated the regression equations are not signifi- egg size (i. e., [length (mm)] x [width cantly different in slope between any paired (mm)]2, and called egg volume for conven- populations whose regression lines are toler- ience' sake) is adopted in the following able for covariance analysis. On the con- discussion on egg size. trary, they differ significantly in elevation 3. Results (P<0.05) among most of these populations, suggesting the difference in body 3-1. Body Size of Berried Female shape that has been noticed and is easily The size of the berried female varies discernible by the layman's eye. with the population in terms of different 3-2. Egg Size localities (Figs. 2, 4, 5). Although the ber- As has been pointed out by KAMITA ried females are larger early in the breeding (1961), the sizes of eggs in the advanced season (SAITO and YAMADA, 1954; OKUBO, developmental stages are larger than those 1964; KAMBARA et al., 1967), most of the of the earlier stages. The average volumes specimens examined in the present study of eyed eggs, and similarly their average were collected in the peak period of the weights, are 1.2 to 1.8 times as large as breeding season, namely, from late May those of pre-eyed eggs in all of the popu- to July, and the seasonal variation in size lations studied. However, the variation in may not be taken into account in the anal- egg volume among the eggs at any certain ysis of the results. The size distribution developmental stage within a population of the berried females is nearly normal in is quite small, the coefficient of variation all populations except that of Lake Ohnuma being about 10 %, and that within a brood 188 Geographical Variations of a Freshwater Shrimp NISHINO 189 is mostly less than 7 %. The population of Lake Ohnuma (No. 22) is the exception in that the large females (No. 22**) bear slightly and similarly larger eggs than those of the small females (No. 22*). The size of the egg, therefore, can safely be regarded and treated as the stable character of the population. Among the populations studied, the egg volume varies greatly (Table 1), ranging from O.34 in Lake Biwa (No.1) to 2.30 in Lake Akan (No.26) in pre-eyed eggs. The populations from the River Yodo (No.3), leading from Lake Biwa to Osaka Bay, and the River Kizu (No.5), a branch flowing into the Yodo, also show slightly smaller eggs, with some individuals (No.2 and 5) bearing extremely small eggs comparable to those in Lake Biwa. The populations from Mandai-ike (No.4) and the River Tojo (No.6) in the same Kinki District also show egg sizes as small as Fig. 3. Mean egg volumes ± SD) of pre-eyed those from the Yodo (No.3) or the Kizu eggs plotted against the latitude of (No.5). The egg sizes of other populations each locality. The value for the River rest on a gradually increasing series start- Hota (No.8) is calculated, using the ratio of mean volume of pre-eyed eggs ing from the value of the Tojo (No.6). to that of eyed eggs of the specimens Generally, egg sizes are relatively similar from neighbouring the River Tomoe.

in populations geographically proximate to one another. The exceptions are the populations in Lake Biwa (No.1), the River Tomoe (No.7) and River Hota (No.8). In Fig.3, the egg volumes of pre-eyed stage are plotted for each population against the latitude of the locality of the populations. There is a recognizable south-north trend (or trends) of increase in egg size, in spite of some exceptions stated above. Figure 7 shows the relationship of mean body weight of berried females to mean egg volume for each population. Popula- tions with larger mean weight of berried. Fig. 2. Mean body lengths ± SD) plotted females, such as those of the large fe- against the latitude of each locality. males of Lake Ohnuma (No.22**), Lake No.22* and No.22** indicate the value Harutori (No.24) and Lake Akan (No.26), of small and large females in Lake Ohnuma, respectively. produce larger eggs. In addition, although 190 Geographical Variations of a Freshwater Shrimp they produce eggs of similar size, females from small ponds tend to be smaller than those from neighbouring lakes and rivers. The females of Mandai-ike (No.4) are smaller than those of the River Yodo (No.3), those of Kagami-ike (No.9) are smaller than in Lake Ikeda (No.10), those in a pond in Aomori (No.16) are smaller than in Lake Towada (No.17), and those of Matsumoto Castle moats (No.25) are smaller than in Lake Suwa (No.21). 3-3. Brood Size Brood size here means the number of eggs carried by a female at one time, and

Fig. 5. Regression lines of brood size on body length for the populations. Each line is drawn for the actual range of body length measured.

it differs among the individuals even within a given population (Fig.5). The maximum brood size recorded was 909 from Lake Biwa (No.1), and the minimum was 46 from Aomori (No.16). The log of brood size shows a significant linear correlation with the log of length of females (P<0.02) for all populations except that of Kagami- ike (No.9), a pond in Fukuoka (No.14), and that of Matsumoto Castle moats (No. 25), in all of which specimens were fewer than in other waters. Covariance analysis weight on Fig. 4. Regression lines of body shows that the slopes of the regression body length for the representative lines are not significantly different between populations. Each line is drawn for the actual range of body length measured. any paired populations whose regression NISHINO 191 lines are tolerable for the analysis, but the elevations of the regression lines are significantly different (P

Fig. 7. Relation of mean body weight ± SD) to mean egg volume ± SD) of pre-eyed eggs among the populations. 192 Geographical Variations of a Freshwater Shrimp

Fig. 8. Relation of mean brood size (± SD) to mean egg volume (± SD) of pre-eyed eggs among the populations. largest mean body weights. The popula- hand, the populations having the largest tions exhibiting the largest mean relative mean relative brood size at respective mean brood size at respective mean body weights body weight (in Fig.6) retain large and (in Fig.6) are those having the smallest similar mean brood sizes (in Fig.8). mean egg volume among the populations 3-4. Reproductive Effort of similar mean body weights (in Fig.7). The relative brood weight, i. e., the The mean brood size was calculated from value of [weight of eggs carried by a the actual number of eggs counted for all female] / [berried female body weight], is berried females when the specimens were plotted against the respective female body relatively few, or basing on the length weight for the representative populations frequency distribution of berried females (Fig.10). There is no definite trend of and the regression between the brood size variation in this value with body weight and the length when a large number of within each of most populations; instead, berried females were available. The mean the relative brood weight remains at a brood size with the range of standard certain level, differing slightly from popu- deviation is plotted against the mean egg lation to population. volume for each population in Fig.8. The relative brood weight can also be There is no consistent relation between expressed by [relative brood size] x [weight these two values, and the mean brood size, of a single egg]. The relationship between including that for Lake Biwa (No.1), mean relative brood size and mean egg remains within a limited range regardless volume among the populations is shown in of mean egg volume. There is also no Fig.11. The mean relative brood weight discernible geographical trend in mean shows only a small range of variation, as brood size in contrast to mean egg volume is easily deduced from the values of [mean as mentioned before, but populations from relative brood size] x [mean egg volume], small ponds show smaller mean brood sizes shown in Fig.11. The mean egg volume than those from lakes and rivers among is almost inversely proportional to the neighbouring populations. On the other mean relative brood size. NISHINO 193

Fig. 9. Relations of relative brood size to body weight _for the representative populations. Symbols mean pre-eyed egg (○), eye pitted egg (△), and eyed egg (×).

kilograms of shrimps from Lake Biwa 4. Discussion yearly for the past several years by the Palaemon paucidens is fished commercial- fishermen. However, no specimens exam- ly in several lakes and has often been ined from this lake bear eggs as small as introduced from one body of water to those in Lake Biwa. For most of the other another, intending to improve fishery re- waters, no information is available on sources. For instance, the population of whether the population is indigenous or Lake Ohnuma in Hokkaido was established introduced. In this connexion, the materials through the introduction of shrimps from treated in this study are regarded as repre- an adjacent river in 1909 (HANDA and senting the population of the locality in ARAKI, 1930), and that of Lake Towada the following discussion. from Lake Hachirogata in 1905 (MATSUI It is confirmed that the maturation age and WAINAI, 1937). Lake Shinji was of this species is 1 year for the populations confirmed to have been natively inhabited from a pond in Fukuoka (MINEI, 1972), a by this species in 1961 (HARADA, 1968), pond in Kagawa (KAMBARA et al., 1967), but it has been receiving some hundred Lake Biwa (HARADA, 1966), Mae-ike 194 Geographical Variations of a Freshwater Shrimp

Fig. 10. Relations of relative brood weight to body weight for the representative populations. Symbols mean pre-eyed egg (○), eye pitted egg (△), and eyed egg (×).

(OKUBO, 1961), Lake Towada (MATSUI females from Lake Ohnuma, but they do and WAINAI, 1937) and reared specimens not state indubiously whether they took from a pond in Hyogo (TAKEDA, 1972) . total lengths usually measured at that time On the contrary, the populations from Lake or body lengths. If the sizes they give are Ohnuma (HANDA and ARAKI, 1930) and total lengths, the sizes of these females a pond in Sapporo (SAITO and YAMADA, correspond to those of small and large 1954) are confirmed to breed at age 2. From female groups, suggesting that these two the findings mentioned above, most of the groups of Lake Ohnuma are ages 1 and 2, berried females treated in this study, respectively. The berried females from except those of the Hokkaido District, can Lake Akan and Lake Harutori are decisive- be regarded as age 1. HANDA and ARAKI ly larger than the large females from (1930) give the sizes of 1-and 2-year old Lake Ohnuma and, therefore, they can NISHINO 195

Fig. 11. Relationship between mean relative brood size (± SD) and mean egg volume (± SD) in pre-eyed eggs among the populations. The diagonal lines represent the lines on which relative values of [mean relative brood size x mean egg volume] are 1.25, 1.00, and 0.75, respectively, when the value of the population in Lake Biwa is taken as 1.00. safely be regarded as age 2 or more. the amounts of time or energy allocated In the opening paragraph of his paper, for different requirements, but rather the CODY (1966) wrote of the "Principle of recognition of the realization of one pattern Allocation" as follows: "It is possible to of allocation as a strategy for successful think of organisms as having a certain reproduction. If the amount of energy or limited amount of time or energy available substance which can be allocated by a for expenditure, and of natural selection female to the next generation in the form as that force which operates in the alloca- of reproductive matter, that is eggs pro- tion of this time or energy in a way which duced, can not exceed a certain level, a maximizes the contribution of a genotype larger relative brood size can only be at- to following generations. This manner of tained by reducing egg size. In Palaemon treatment of problems concerning the adap- paucidens, body size differs geographically tation of phenotypes is called the Princi- among the populations; on the contrary, ple of Allocation (LEVINS and MAC- mean relative brood weight remains within ARTHUR, unpublished), and one of its ap- a limited range among them, suggesting plications might be the formulation of a that the reproductive matter produced by general theory to account for clutch size a female is relatively similar in quantity in birds."It is apparent that CODY does among these populations. Based on the not mean the simple relationship among result of nearly constant mean relative 196 Geographical Variations of a Freshwater Shrimp brood weight, the mean egg volume should study. All marine and brackish species are be inversely proportional to the mean rel- also regarded as of the common type, ative brood size. As has been described in whereas Palaemon modestus is assigned the preceding section, mean relative brood to that of the abbreviated type. size and mean egg size vary correlatively The pattern of intraspecific variation in in this manner. egg size in Palaemon paucidens appears to Although brood size is greatly influenced be characteristic. Egg size remains con- by the body size of the mother shrimp stant within any population except that from in a population, relative brood sizes are Lake Ohnuma, and displays great variation similar among females. The difference in among the populations. In fish, both cases relative brood size is apparent between the are known, where egg size varies with population of Lake Biwa and that of other body size, as in rainbow trout (KATO, 1975) waters. However, mean brood sizes are and catfish (DAVIS, 1977), or remains similar among the populations having the constant, as in some species of cichlids largest mean relative brood size at respec- (FRYER et al., 1972), within a population. tive mean body sizes. The other populations In the case of rainbow trout (KATO, 1975), have smaller mean brood sizes within a egg sizes are relatively similar only within certain range. It is evident that there is an a year class. AZUMA (1973c) reports the undeniable interrelationship among mean variation in egg size between the popula- body size, mean relative brood size, and tion for ayu-fish, Plecoglossus altivelis, but mean brood size, though its biological in this case egg size varies with body size basis has to be proved. within a population. By comparison of The intraspecific difference in egg size has three local populations of a goby, Tri- been little noticed for freshwater shrimps, dentiger obsculus, KISHI (1978) concludes and KAMITA (1961) denies its occur- that egg size of each population remains rence for Palaemon paucidens. As has almost constant regardless of female body been shown in the preceding section, this size, but the egg size and body size of the is not the case with the present findings. females in the lake population are decisive- Kuso (1942) recognizes two groups of ly smaller than those from the river and species of the genus Leander (— Palae- estuary populations. No such pattern of mon) in Japan and adjacent areas in terms variation in egg size of Palaemon pauci- of egg size. The large egg group includes dens has not been reported, as far as I paucidens, miyadii and modestus, all fresh- know. water species, and the small egg group Possible combinations can theoretically comprises marine and brackish species. be deduced for the relations of egg size, According to the egg sizes given by him relative brood size, relative brood weight for these groups, however, Palaemon and brood size to body weight within a paucidens from Lake Biwa should fall into population, if egg size and brood size in- the small egg group. KWON and UNO (1968) crease with body size, or egg size remains distinguish three types of larval develop- constant and brood size increases (Fig.12 ment of carideans after SOLLAUD (1923), A). Only three cases of them are known and consider Palaemon paucidens as the to occur actually in aquatic fishes and species of the common type with no abbre- shrimps, as far as I can study. The first is viation, basing on YOKOYA (1931), whose the case represented by Palaemon pauci- measurements of egg specimens correspond dens, whose egg size, relative brood size to those of the largest eggs in the present and relative brood weight remain almost NISHINO 197

Fig. 12. Brood habit, or the relationship between egg size and brood size in relation to mother body size, found in a species or in a population. (A). Possible combinations of the relations of egg size, relative brood size, relative brood weight, and brood size to body size (abscissa) within a population. Each line shows merely the tendency of being increasing, constant, or decreasing. (B). The relations of population means of the same values to mean body weights (abscissa), realized by the populations of Palaemon paucidens and Plecoglossus altivelis. Open circles represent the populations from lakes and rivers, and solid circles from ponds for Palaemon paucidens. For Plecoglossus altivelis, 'A' means early ascending group from Lake Biwa, 'B' late ascending group, 'C' lake population of small size, and 'R' the river population. similar regardless of body size (I in Fig. compared among local populations, but 12 A). The second case is seen in the carp, only a few sources for several species CyPrinus carpio (HULATA et al., 1974), enable this (Fig.12 B). In Palaemon whose egg size increases with body weight, paucidens, although both mean egg size but relative gonad weight (the ratio of and mean relative brood size differ among the populations, mean relative brood weight gonad weight to body weight) is independent of body size (V). The third is found and mean brood size are within a limited with the perch, Perca fluviatilis (CRAIG, range. In Plecoglossus altivelis, mean 1974). Its egg size and relative gonad relative gonad weight is nearly identical weight increase with body weight, but among the three populations from Lake Biwa. However, mean egg size slightly relative egg number (the ratio of egg number to body weight) is independent of increases with mean body size, and mean egg number distinctly increases among body size (IV). In addition, SHATUNOVSKII them (AZUMA, 1973b). On the contrary, (1964) * reports that in the flounder, Pleuro- nectes (= Platichthys) flesus, the relative mean egg size and mean relative egg egg number increases with body size, and number for the river population are much eventually this species falls into either the different from those of the populations third (III) or the eighth (VIII) case in from Lake Biwa, although mean relative Fig.12 A. gonad weight is similar (AZUMA, 1973c). The combination of the relations of mean Apparently, in these species, mean egg egg size, mean relative brood size, mean size, mean relative brood size, mean rela- relative brood weight, and mean brood size tive brood weight, and mean brood size to mean body weight can similarly be are not linearly correlated with mean body

* Cited from BAGENAL (1967). size, as is seen in the relations of egg size, 198 Geographical Variations of a Freshwater Shrimp relative brood size, relative brood weight, and brood size to body size within a population. It is obvious that egg size and relative brood size are almost inversely correlated in Palaemon paucidens, and their variations can not be treated independently. Among the local populations of the species, the variation in egg size generally tends to be greater at higher latitudes and less at lower latitudes. The populations of Lake Biwa, the River Tomoe and River Hota are the exceptions, and their eggs are far smaller than those of neighbouring populations. To explain selection toward the production of larger eggs, adaptation to colder or unfavourable condition is one conventional reasoning. The annual mean surface temperatures for each locality are plotted a- gainst the latitude in Fig. 13, and the relationship between egg volume and annual mean surface temperature among the local-

Fig. 14. Relation of mean egg volume (± SD) of pre-eyed eggs to mean water tern- perature at surface of each locality.

ities is shown in Fig.14. Although water temperatures are not available for certain localities, egg volume has been generally found to correlate more significantly with water temperature than the latitude. BARNES and BARNES (1965) reports for thoracican barnacle that the eggs of boreo- arctic species are remarkable for their large size compared with all other species, and for Balanus balanoides that eggs are larger in populations from the areas where winters are severe and summers relatively Fig. 13. Annual mean water temperature at surface plotted against the latitude of cold, irrespective of the latitude. KAMITA each locality, based on the various (1961) has found that Paratya comPressa sources, published or privately informed improvisa bears eggs larger than those and partly measured by myself, from of Paratya compressa, the former being 1956 to 1978. No.4 is represented by distributed more northward in Japan a nearby pond based on MIZUNO(1961) and No.13 in a river flowing into and the latter more southward. The pre- Lake Ono. sent geographical trend in egg size of NISHINO 199

Palaemon paucidens accords with evidences April, from around 7 ℃, and proceeds in those species mentioned above, and may rapidly in early summer to about 28 ℃ in be explained as an adaptation to temper- July (Fig. 15). The decrease in ternpera- ature condition. A particular exception is ture begins late in autumn and proceeds the population from Lake Biwa, whose slowly. However, deep water tempera- attributes are difficult to be explained on tures below 40 m never rise above 10℃ the same basis suggested above. (Fig.15). Annual mean surface tempera- The remarkable features of the popula- ture of Lake Biwa does not differ much tion in Lake Biwa are more than apparent, from those of other lakes and ponds in the which are evidently expressed in the small same district or at similar latitudes, where- body and egg size and the large relative as, it has much less annual variation in brood size. Lake Biwa is the largest lake temperature. Daily fluctuation in surface in Japan, with a maximum depth of 103.9 temperature in Lake Biwa is also smaller m, a mean depth of 41.2 m, and an area than in others, presumably because of its of 674.4 km2. Accoding to YOSHIMURA great thermal capacity. The seasonal (1936a), it belongs to the category of migration occurring in the population of subtropical lake, with a surface tempera- Lake Biwa adds another aspect to their

ture which never falls below 4 ℃, with a thermal environment. HARADA (1966) distinct thermocline in summer, and has reports that young of Palaemon paucidens one circulation period in winter. Although in Lake Biwa migrate from inshore waters HUTCHINSON (1957) points out that heating to profundal bottoms of more than 40 m in starts early and proceeds slowly in a sub- depth in autumn to pass the winter and tropical lake having a great mean depth, return to shallow waters again in spring the rise in surface temperature starts to grow and breed. The longer exposure comparatively late in Lake Biwa, in early to low temperature may, as is generally admitted in many animals, lead to the retarded growth in the Lake Biwa population, resulting in the small body size and causing smaller maturation size. The fact that the body sizes of the aged-1 shrimps of the population in a pond in Sapporo, that has been confirmed to breed in the second year (SAITO and YAMADA, 1954), are slightly smaller than in Lake Biwa may support this. With the decrease in body size at maturation, the decrease in brood size generally occurs, as is seen among females or among populations. As has been stated repeatedly, the population of Lake Biwa is exceptional, in which larger brood sizes are attained in Fig. 15. Seasonal changes of water temperatures spite of the small body size, resulting in at surface and at bottom of 50 m in exceptionally high relative brood size. depth in Lake Biwa in 1978, and at surface in Lake Shinji in 1960-61 based Being associated with this, an apparent on the survey report compiled by S. decrease in egg size has also occurred. MORI (1962). The extreme decrease in egg size may 200 Geographical Variations of a Freshwater Shrimp

have brought about high mortality of the Towadako Fish Hatchery ; Mr. M. YAMAMOTO, tiny larvae released. In fact, the experi- Suwa Hydrobiological Station, Shinshu Universi- mental results of rearing larvae from eggs ty; Mr. H. MATSUI, Ebra-Infilco Co., Ltd.; Mr. of various populations suggest lower sur- Y. NAKATA, Osaka Kyoiku University; Dr. K. vival rate of the larvae from Lake Biwa HAYASHI, Shimonoseki University of Fisheries. Also, Mr. K. TATSUKAWA, Ocean Research Insti- in the same rearing conditions (NISHINO, tute, Tokyo University, and Dr. K. MIZUGUCHI, unpublished data). Further, no females Tokyo University of Fisheries, kindly allowed have been found in Lake Shinji that are me to examine specimens from the River Kamo bearing eggs of a size comparable to those and River Obitsu. Finally, I am indebted to Mr. in Lake Biwa, even though shrimps have A. KAWABATA and Mr. T. UEDA, Otsu Hydrobi- been repeatedly transplanted into there ological Station, for their assistance in collection, from Lake Biwa. The populations from and to Hokkaido Fish Hatchery for allowing use the River Yodo and River Kizu, both of of their records of water temperatures from which are connected with Lake Biwa, Lake Ohnuma, Lake Shikotsu and Lake Akan. seldom involved females with small eggs. 摘要 These findings suggest that the larvae 1)日本およびその近傍に広く分布する陸水産スジ from the population of Lake Biwa can エビPalaemon paucidensの親の大きさ・一腹卵数 hardly survive in the waters but Lake ・卵の大きさの地理的変異を調べる為に様ざまな湖・ Biwa. Probably, the conditions surrounding 池・河川の28個所から採集した抱卵雌について,体 the population in Lake Biwa are favourably acting to support better survival of the 長・体重・一腹卵数および一雌ごとに10個の卵を取 tiny, frail larvae through its less variable, りその長径と短径を測定,卵容積を算出した 2)抱卵雌の平均体長は個体群間で異なり,北海道 or stable, states of conditions, as well as the great expansion of its water body. 産では大きく,琵琶湖産や大阪の溜池産では小さかっ The high relative brood size achieved た. through diminishing the egg size may 3)卵容積は,各個体群内では雌の大きさにかかわ thus be regarded as an adaptive strategy りなくほぼ一定であったが,個体群間では高緯度のも of allocation that can be adopted only by の程大きい傾向があり最大の阿寒湖産の卵容積は最小 the population in Lake Biwa. の琵琶湖産の約7倍であった. 4)一腹卵数は同一個体群内では雌の大きさに伴い Acknowledgements 増大するが,相対抱卵数はほぼ同一の値を示した.個 I wish to express my heartfelt thanks to Prof. 体群間では,平均相対抱卵数と平均一腹卵数は,琵琶 E. HARADA,Seto Marine Biological Laboratory, 湖産以外では,雌の平均体重にかかわりなくある巾の Kyoto University, for his many valuable sugges- 中にあった,琵琶湖産では,平均相対抱卵数は著しく tions and critical reading of the manuscripts. I 高いが,平均体重が著しく小さい為に,平均一腹卵数 am also grateful to Prof. H. KAWANABE,Depart- は他の個体群と同様のレベルに留まった. ment of Zoology, and Dr. T. NARITA, Otsu 5)相対抱卵重は・各個体群内・個体群間ともに著 Hydrobiological Station, of Kyoto University, しい違いはなく,各個体群の平均相対抱卵数と平均卵 for reading the manuscripts, and to the members 容積の間にはほぼ逆の相関関係が認められた. of Otsu Hydrobiological Station for their useful 6)同一個体群内における親の体重に対する卵の大 discussion and criticism. I also would like to acknowledge the generous assistance of the fol- きさ・一腹卵数・相対抱卵重の関係のあり方には,考 lowing in collecting materials: Ms. T. ITO, えうる幾つかの組合わせがあるが,実際の水生動物で Hokkaido Fish Hatchery; Mr. K. ISHINO,Faculty はスジエビを含めてこれまで3つの場合しか知られて of Fisheries, Hokkaido University; Dr. S. HIRAI, いない. Asamushi Marine Biological Station, Tohoku 7)卵の大きさが例外はあるが高緯度で大きい傾向 University; Mr. N. SATOand Mr. H. SHIRAHATA, を示すのは,冷たい温度条件に対する適応であると推 NISHINO 201

測された.例外の1つである琵琶湖の個体群では,そ large crustaceans. p. 555-603. In: The Inter- の生活史の故に長期間低温条件で棲息することとなり, im Report of the Biological Research Groups

親の大きさの小型化が惹き起こされたと考えられ,こ of Organic Resources in Lake Biwa. (in の個体群では生殖物質の分配の適応戦略の1つとして, Japanese) HARADA,E. (1968) : Ecology and biological pro- 卵の大きさを減少させて高い相対抱卵数を実現し,そ duction of Lake Naka-umi and adjacent れにより,親の大きさの減少に伴う平均一腹卵数の減 regions. 5. Seasonal changes in distribution 少を補ったと解釈された. and abundance of some decapod crustaceans. Spec. Publ. Seto Mar. Biol. Lab., Series II. References Part II: 75-103. AZUMA, M. (1973b) : Studies on the variability HULATA, G., R. MOAVand G. WOHLFARTH(1974) : of the landlocked Ayu-fish, Plecoglossus alti- The relationship of gonad and egg size to velis T. et S., in Lake Biwa. III. On the weight and age in the European and Chinese differences in the process of maturation, races of the common carp, Cyprinus carpio spawning habits, and some morphological L. J. Fish. Biol., 6:745-758. features of each population. Jap. J. Ecol., 23: HUTCHINSON,G. E. (1957) : A Treatise on Lim- 147-159. (in Japanese) nology. Vol. 1. Geology, Physics, and AZUMA,M. (1973c) : Studies on the variability of Chemistry. Wiley. the landlocked Ayu-fish, Plecoglossus altivelis KAMBARA,N., S. UCHIKOSHIand U. ITO (1967) : T. et S., in Lake Biwa. IV. Considerations The Investigation on freshwater shrimps in on the grouping and features of variability. a pond of Kagawa Prefecture. Bull. Kagawa Jap. J. Ecol., 23 : 255-265. (in Japanese) Pref. Fish. Exp. Sta.,: 43-44. (in Japanese) BAGENAL,T. B. (1967) : A short review of fish KAMITA, T. (1961) : Studies on the Freshwater fecundity, p. 89-111. In: S. D. GERKING(ed.), Shrimps, Prawns and Crawfishes of Japan. The Biological Basis of Freshwater Fish Sonoyama Shoten. (in Japanese) Production. Blackwell. KATO, T. (1975) : The relation between the BARNES, H. and M. BARNES (1965) : Egg size, growth and reproductive characters of rain- nauplius size, and their variation with local, bow trout, Salmo gairdneri. Bull. Freshwater geographical, and specific factors in some Fish. Res. Lab., 25 : 83-115. (in Japanese) common cirripedes. J. Anim. Ecol., 34: KISHI, Y. (1978) : Egg size difference among 91-402. three populations of the goby, Tridentiger CODY, M. L. (1966) : A general theory of clutch obsculus. Jap. J. Ichthyol., 24 : 278-280. size. Evolution, 20: 174-184. KUBO,I. (1942) : Studies on Japanese Palaemonid CRAIG, J. F. (1974) : Population dynamics of Shrimps. III. Leander. J. Imp. Fish. Inst., erch, Perca fluviatilis L. in Slapton Ley,p 35 : 17-85. Devon. Freshwat. Biol., 4: 417-431. KWON, C. S. and Y. UNO (1968) : The larval DAVIS, T. L. O. (1977) : Reproductive biology of development of Palaemon modestus (Heller) the freshwater catfish, Tandanus tandanus in the laboratory. La Mer, 6 : 263-278. MITCHELL,in the gwydir River, Australia. II. MATSUI,I., T. WAINAI(1937) : Ecological investi- Gonadal cycle and fecundity. Aust. J. Mar. gations of a freshwater shrimp, Leander Freshwater Res., 28: 158-169. paucidens DE HAAN in Lake Towada. Jap. FRYER, G. and T. D. ILES (1972) : The Cichlid J. Limnol., 7: 31-41. (in Japanese) Fishes of the Great Lakes of Africa. Oliver MINEI, H. (1972) : On the culture and ecology of & Boyd. the Japanese freshwater shrimps. Nature HANDA, Y. and K. ARAKI (1930) : Limnological Study, 18: 62-68. (in Japanese) Survey. part 1. Oh-numa, Ko-numa and OKUBO,H. (1961) : Ecological studies on a fresh- Junsai-numa. In: Fishery Survey Reports, water shrimp (Leander paucidens DE HAAN) Hokkaido Fisheries Experimental Station, 21. in farm ponds. I. Bull. Freshwater Fish. (in Japanese) Res. Lab., 11: 57-68. (in Japanese) HARADA,E. (1966) : The interim report of the RATHBUN, M. J. (1902) : Description of new dec- 202 Geographical Variations of a Freshwater Shrimp

apod crustaceans from the west coast of condensation progressive de I'ontogenese. Japanese stalked-eyed crustaceans. Proc. U. Bull. Biol. France et Belg., 57: 509-603. S. Nat. Mus., 26. TAKEDA, F. (1970) : Studies on breeding in SAITO, S. and J. YAMADA(1954) : An ecological caridean shrimps. Bull. Fish. Exp. Sta. study on Leander paucidens DE HAAN obtained Hyogo-Ken., Spec. Rep., 1. (in Japanese) by artificial rearing and in nature. Mem. TATSUKAWA,K. (1977) : Ecology and distributions Fac. Agric. Hokkaido Univ.,: 213-220. (in of shrimps and prawns in inland waters. Japanese) Anima, 51: 25-30. (in Japanese) SHATUNOVSKII,M. I. (1964) : Some factors in YOKOYA,Y. (1931) : On the metamorphosis of the fecundity dynamics of two populations of two Japanese freshwater shrimps, Paratya flounder (Pleuronectes flesus L.). Nauch. compressa and Leander paucidens, with Dokl vyssh. Shk., 1: 27-30. reference to the development of their SHOKITA,S. (1973a) : Abbreviated larval develop- appendages. Jour. Coll. Agric. Imp. Univ. ment of the freshwater prawn, Macrobrachi- Tokyo, XI. no. 2: 75-150. um shokitai FUJINO et BABA (Decapoda, YOSHIMURA,S. (1936a) : A contribution to the Palaemonidae) from Iriomote Island of the knowledge of deep water temperatures of Ryukyus. Annot. Zool. Jap., 46: 100-110. Japanese lakes. Part 1. Summer temperature. SHOKITA, S. (1975) : The distribution and speci- Jap. J. Astr. Geo., XIII. no. 2: 61-120. ation of the inland waters shrimps and prawns

from the Ryukyu Islands. I. Bull. Sci. & (著者:西野麻知子,京都大学理学部附属大津臨湖 Eng. Div., Univ. Ryukyus, 18 : 115-135. 実験所,大津市下阪本;Machiko NISHINO, Otsu (in Japanese) Hydrobiological Station, Kyoto University, SOLLAUD,E. (1923) : Le developpement larvaire Shimosakamoto, Otsu 520-01, Japan) des Palaemonidae. I. Partie descriptive. La Accepted: 10 March 1980