STOCK EVALUATION, BIOLOGY AND AQUACULTURAL PRODUCTION OF SPINY EEL
ABSTRACT THESIS SUBMITTED FOR THE DEGREE OF MottOT of $I)tlO!BlQptlP IN ZOOLOGY
By MD, SERAJUDDIN M. Phil. (Alig)
FISHERY SCIENCE SECTION DEPARTMENT OF ZOOLOGY ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA) 1994 JAhstraci Abstract
The work done on the biology of Indian freshwater fishes mainly deals with the carps, murrels and the cat fishes. But no attention has been paid to the study of the biology of the spiny eel, Mastacembelus armatus (family: Mastacembelidae) , which is palatable and nutritive. The spiny eels sold in the market are brought almost entirely from their natural population. In view of their dwindling natural population, the situation demands that scientific methods be applied for culturing these eels. But, development of a suitable method for their aquaculture is inconceivable without a sound knowledge of their biology. Keeping in mind the poucity of information on the biology of Mastacembelus spp. in general, an attempt was made here to study the biology of M. armatus, which is the most important of the four species of the genus Mastacembelus found in India.
The spiny eels occur in tropical Africa and Asia only. In all there are thirty- three species of freshwater spiny eels which have been housed in four genera, two of which namely, Macrognathus and Mastacembelus are under sub-family Afromastacembelinae. Species of the genus Mastacembelus found in Indian region are M. armatus, M. oatesii, M. 1 alboguttatus and M. dayi. Out of these, the species M. alboguttatus and M. dayi are rare in occurrence. As far the remaining two species, while M. oatesii attains a length of about 3.7 cm, and being of a small size is of no interest to fisheries, M. armatus attains a length up to 65 cm and is considered the largest spiny eel found in India. M. armatus is, therefore, of interest to fisheries, the more so because it is considered to be very good table fish particularly in the plains of India where it is very popular especially when sold in live condition. The spiny eel, M. armatus, is restricted to Asia. It has been reported from Pakistan, Sri Lanka, Bangladesh, Myenmar through Thailand, Malaysia and southern China. It occurs in a variety of freshwater habitats in the plains as well as in the hills of India. It is common in rivers, lakes, ponds, streams and estuaries. The fish patrols a body of water throughout its length and breadth but spends major part of its life at the bottom of the water. The samples were collected from Kalinadi, a tributary of the river Ganga at Aligarh for stock analysis study. Various morphometric and meristic characters alongwith the study of length -weight relationship were used for stock discrimination. Riverine population of M. armatus was found to consist of two stocks which have been denoted here as stocks A and B. These stocks were sympatric and differed m a number of morphometric and meristic characters. The 2 regression of different body measurements like standard
length, head length, snout length, caudal fin length,
predorsal length, body depth, body width, caudal fin depth,
interorbital width and optic diameter on totat length was
studies, as a result of which a linear relationship was
noted to occur between them in the fishes of both the
stocks. Correlation of coefficient in all the above
mentioned relationship was highly significant. Various body
proportions are expressed here as percentage of total
length. Significant difference in the sets of characters
head length/total length, standard length/total length, pre
dorsal length/total length, body depth/total length, body
width/total length have been found between the fishes of
stocks A and B. The equations obtained for length-weight
relationships in the fishes of these two stocks were also
different. Appreciable difference in growth of weight
relative to length was noticeable in these two stocks.
Stock A which demonstrated faster growth (weight per unit
length WPUL = 3.75g) occurred with 37.12% frequency, whereas stock B (WPUL =1.85 g) was more preponderant (62.88%). The spiny eel, M. arwatus is highly predacious in nature and prefers live aquatic crustaceans and insects as their food.
Well developed dentition, strongly built stomach and short intestine are some of the characteristics which were related to the fish's dietary composition. M. armatus has an uneven gill arch surface in place of gill rakers. There was nc
3 major shift from a basically carnivorous orientation in the feeding activity of this fish during its various stages of growth. Gut contents analysis showed that macrocrustaceans (especially shrimps) and forage fish were the main food of the adults while annelids and aquatic insects were taken by the young specimens. Molluscs and aquatic vegetations were consumed as incidental items. Gut length/ body length ratio of the fish varied from 1:0.50 to 1:0.68, foraging activity fluctuated with season. Feeding intensity was high in early maturity stages and was got relatively lower in fish with ripe gonads. Adult specimens consumed more food in summer than winter and rainy season. Food intake in younger specimens was greater in post-monsoon period and autumn, but pronounced feeding activity was observed in the month of October. Extremely low feeding was observed in the month of December. In adults maximum number of empty guts were found during spawning and in winter.
The study of length-weight relationship of M-arwatus revealed that the fish did not follow the cube law strictly and the weight increased was at a rate more than the cube of the length in both juveniles and adults. A significant difference was noticed in the value of 'b' among juveniles, males and females. The equations for length-weight relationship are W = 7.401 x lo'^'^ L3.3695 ^^^ juveniles, W = 1.415 X 10°^ L^-^^^^^ for males, W = 7.8 x 1C^°^ j_3.60328 fQ^ females and W = 4.4 x 10"°'^ L^-29558 ^^^ ^j^^ data of males and females combined. These length-weight relationship equations indicate that the females increased faster in weight than males. The significant variation of the value 'b' from expected cube law was tested by a 't' test. The values obtained for both males and females are highly significant at 5% level. The value obtained from covariance analysis for the difference between the slopes of regression lines obtained for males and females is 5.44 (d.f. 1,322), suggesting that separate equations are required for the two sexes. Breeding process of the fish was examined. Population of M.armatus was slightly dominated by males. The male : female ratio ranged from 1:0.50 to 1: 1.2 with the average ratio being 1:0.8. Sex ratio varied with different size range of this fish and with change in season. Gonads were differentiated into five phases of maturation with stages, I, II, III, IV and V representing immature virgin, maturing virgin and recovering spent, ripening, ripe and spent specimens respectively. Seasonal activities of the gonads were clearly demonstrated. The gonado-somatic index was related to the stages of development; it increased with the development of gonad. In both the sexes high values of gonado-somatic index was recorded during the period Kay through July. Change in the index was more marked in females . Spawning in M. ariuatus commenced in late June/early July. Spawning coincides with onset of monsoor..
5 Occurrence of ripe individuals upto late August/early September shows the extent of the spawning of this fish. The fish spawns only once in a year. There was no evidence of fractional spawning as oocytes in each individuals were all of same diameter showing only one batch. Fecundity increased with growth in length and weight of fish of the size 12-48.2 cm produced 927-7409 eggs. The fecundity 'factor' was 63 egg cm"-^ body length and 29 eggs g"""- body weight respectively. Fecundity-body length progression was stronger than fecundity-body weight relation. These relationships have been quantitatively evaluated. The two experiments done in connection with the culture of fry of M. armatus were conducted in nursery pond and cemented cistern, using artificial feeding. The stocking rate of fry was 15,000/ha in both the cases. In nursery pond the experiment was carried out for 100 days. It was run for 3 0 days in the cemented cistern. The rate of body weight increment was 2.835 g/month in the nursery pond and 3.09 g/month in the case of cemented cistern. The specific and relative growth rates were 2.107% and 716.1 % respectively in the case of fish kept in nursery pond and 3.21% and 161.75% respectively in the case of fish kept in the cemented cistern. In the nursery pond with an area of 263 m the total yield was found to be 2.5 kg (estimated as 93.1 kg/ha/100 days) in 100 days of cultivation on 60% survival. STOCK EVALUATION, BIOLOGY AND AQUACULTURAL PRODUCTION OF SPINY EEL
THESIS SUBMITTED FOR THE DEGREE OF ®ottor of ^Iitlosioplip IN ZOOLOGY
By MD. SERAJUDDIN M. Phil. (Alig)
FISHERY SCIENCE SECTION DEPARTMENT OF ZOOLOGY ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA) 1994 T4951 DEDICATSO
TO
MY fARSNTS A T£A\CH£kS Dr. Astf A. Kli^ti M.Sc, Ph.D. (Alig-! Res. •.Gulmarg Colony, Reader : Girls College Road, Department of Zoo(ogy, Lai Diggi, Aligarh Muslim University, ALIGARH-202002. ALIGARH-202002. •s- 20569
Date
CEBTIFI8ATE
eet itt- tuitufK^ c»Uf4fi04t4HCHt^ OKCC cecUcctc 4^4tetK,€U w^tC 04. U A^u H^
)c^ .'•VN {Dr. flsif R. Khan} Supervisor CONTENTS
Acknowledgement
General Introduction.
Chapter-1 : Classification and Morphological Characteristics
Chapter-2 ; Habitats and Distribution 15
Chapter-3 : Stock Evaluation 18
Chapter-4 : Food and Feeding Habits 31
Chapter-5 : Length-Weight Relationships 50
Chapter-6 : Reproduction 59
Chapter-7 : Culture 76
Summary 87
References 93 ACI[KO\VliKIM;EA\EKT
"K^K, TS.e.<)Uvi, "De^uvUmctU ^ ^ u^A^4.c 4.u^t.exiAiAi«-n t44A tA-cUi- iA ieim,^ ^M^^ttUttcd.. ^ ttm ^>i€Ue^*cl t^ A^m ^ eA.c (/KM^Ui ^t^KX^m-cttt ^ ^ «^ t^t cx^i.exim.c>tt«,l iiA«x4i, »/ tHii- tA-eAii- ffCtf a-e^ttKyw^C^dfcm-CKt^- ettc tKOKt, tAa-n due t» ^to^- ^• '^- f^4^' ^«<*^' ^e^ta^McetU */ ^»<%i»^. ^. "fft. ^.. (^»« {ii>i»ui€U»^ iUt tA-e iteceiA "Pt^. ^tA.e^ ^UiUUK Siddi^»c, Pt^. "Tft. SAortKCMc ^Ai'Uf.fftwU, Pt^^. '7H^*Ht tAcix eKca^i'Uf.t^ctKeHt etrnd j^cw fkA«x^CtUK<^ t^Xr6^n^)U«^ ^ciiiCied. 1 a-Mc decfttt^ Cttdeited t<^ ^t. SH^^d fl'« ^»»6»^, j^ftt tA.e p^UH^cc-t ttou-CCe A-e to^A in i,ea,diK(^ nnd ie 1 a.m a.Ci,» CAOLKA^C A» m^f e&liea.<^ci ^t. ("TfCCAi^) tfC. "peUcMt^, %>t, f4^<}ue me it Mc^it P."p. "^eAHt^K. "TfOt. 7Kd. 7::/UUd Siu^lUA. TfOt. C'^^d Sci^U. TfOi. ^fi "U/^tdi^ ^U to e«^Mce, ^ u^AieA ^ c<*« exfneAO. ttuf iitde/ftedice ffOi. /46^dM^ ^CAHUIH UAA^^-C tcitlxiKf e^^o^ttd A^ue ptixced Mce it tA-e pA^4e>U ^H tAe fnaeKt e^Ktexi, ^ (u 'TH'U-i^exteX Srui^, MU^ «^r ^»t Ae^ deo^ti»K, utttuMi ete<^wia.^^4H.e*U, itppiee^^ttcaH. iCKde%it /AtttAi OA-e *6t(» due t« ^^ndCun ^o-un-ecl »^ ^^"Ueuitwut-l T^eaetvicA 1H tAe t(X4t, *) a.U(x u^Uli to exp%e^ m^ HeAxt ^eU tA/ticAi to TfOi. ItvtCt} 't(4U^x>t. "Tft^. ^ M. Serajuddin Aligarh Qe^natal Ontroduction General Introduction Fisheries basically started as a "capture fisheries" from the natural resources such as ponds, lakes, reservoires and rivers etc. The primary goals of fisheries development in India are the augmentation of fish production in order to combat malnutrition because fish is a rich source of animal protein, fat and vitamins A and D, and to export the fish and its products in order to earn foreign exchange. Besides these, the development of fisheries in the country holds the promise of generating employment specially in rural sector. Fish production is an age old practice in India, but its being run here on scientific lines and as an industry is relatively recent. It is encouraging to note that as a result of the employment of modern techniques fish production has increased 6 times here since the independence of the country. Being located in the monsoonal belt. India receives good rainfall. As a result, this country has extensive fresh water and brackish water bodies available for aquaculture. The fresh water bodies are in the form of ponds and tanks (2.21 m ha), reservoires (1.97 m ha), beels and oxbow lakes (1.29 m ha) and rivers and canals (1,64121 Km) . However, out of this large area of freshwater bodies a total of only about 0.4 million hectare has been brought 1 under aquaculture so far. As a result, out of the total fish production of 43.64 lakh tonnes in the country during 1992-93, 25.75 lakh tonnes came from the marine resources and the contribution of inland water bodies was 17.89 lakh tonnes. India has so far been a carp country and the techniques of induced breeding and development, hatching, rearing and nursing of the three Indian major carps and the three exotic carps have revolutionized the freshwater aquaculture. It would not be out of the place to mention here that the fishery developmental research was originally started as an experiment in Bengal and Kerala during the early part of this century. Earlier workers in the field of fishery biology like Hora (1921), Hornell and Naydu (1924), Devanesan and John (1940), Chidambaran (1950),Nair (1951), Bhimachar and George (1952), Vijayaraghavan (1953), Seshappa and Bhimachar (1954), Mohammed (1955), Pradhan (1956), Ganapati and Srinivasarao (1957) , Balakrishran (1957) , Nayak (1960), Noble (1962), Radhakrishnan (1962), George and Banerjee (1964), Kegwade (1964), Banerjee (1969), Rao (1970), Luther (1973), Sekhran (1974), Diophode (1974), Kumari and Nair (1979), Rao (1981), James and Badrudddin (1981), Datta and Das (1983), Murty (1983), Vinci (1984) and Jaiswar and Devraj (1989) mainly dealt with the biology of some commercially important marine fishes. Important contributions on the biology of estuarine fishes include 2 Jacot (1920), Hora (1939), Seshappa and Bhimachar (1951), Pillay (1952,1953,1957), Sarojini (1957,1958), Luther (1963), Thakur (1967), Ratnakrishnaiah (1972), Wijeyaratne and Costa (1987), Gowda and Shanbhogue (1988), and Hoda and Qureshi (1989). The work done on the biology of fresh water fishes mainly deals with the carps, murrels and the cat fishes. To mention a few notable contributions in this connection, while Khan (1924), Khan and Hussain (1941), Hora (1945), Mojumdar (1945), Mookherjee and Ghosh (1945), Mookherjee and Ganguly (1951), Chacko and Ganapati (1951), Alikunhi (1952,1956,1958), Jhingran (1952,1957,1959), Das and Moitra (1955a, 1955b), David (1959), Vasisht (1960), Qasim and Qayyum (1961), Natrajan and Jhingran (1963), Kamal (1964,1967,1969), Bhatnagar and Karamchandani (1970), Khan (1972), Bhatnagar (1972), Chakraborty and Murty (1972), Rao and Rao (1972), Khan and Siddiqui (1973), Varghese (1973), Chatterji (1974,1976,1981), Khan and Jhingran (1975), Chatterji et al. (1976 ,1977a,1977b,1977c), Jafri and Mustafa (1975), Pathak and Jhingran (1977), Hameed et al. (1977), Mustafa and Jafri (1978), Chatterji and et al. (1980), Saxena (1980), Joshi and Khanna (1980), Khumar and Siddiqui (1991), Anwar and Siddiqui (1992), Zofair and Mustafa (1992), Madhoosoodana Kurup (1994) and Madhoosoodana Kurup and Koriakosa (1994) worked on the Indian major carps, Alikunhi (1953), Qasim and Qayyum (1961), Qayyum and Qasim 3 (1964a), Qasim and Bhatt (1966,1968) Bhatt (1970), Devraj (1973), Rath and Hejmadi (1976), Balasunder Reddy (1979), Kohli Singh (1989), Kilambi (1986) studied the murrels, Saigal and Matwani (1962), Bhatt (1971,1971a), Bhatt et al. (1977), Majumder (1987), Khan et al. (1988), Tamubi Devi et al. (1992) and Dobriyal and Singh (1993) worked on cat fishes. The commercial breeding of the fishes other than the Indian major carps has not been given any serious attention in this country so far. However, Central Inland Capture Fisheries Research Institute (CICFRI), Barrackpore has recommended a viable culture system for the air-breathing fishes inhabiting the swampy water bodies wihch are unsuitable for carp culture. This diversification in aquaculture is certainly an important step in the direction of obtaining sustainable yields from varied sources of fish production in the country. However, the CICFRI recommendations cover the mass culturing of only a few air- breathing fishes like Clarias batrachus.Heteropneustes fossilis Anabas testudineus and Channa spp. An important omition from this list is the spiny eel, MastaceiTLbelus armatus (Fig.l) (family : Mastacembelidae) , which is quite palatable as a table fish and is nutritive too. The fish being in high demand is indicated by the fact that its demand always exceeds its supply. It may be mentioned here that the spiny eels sold in the market are brought almost 4 entirely from their natural population which, in turn, is showing the signs of dwindling as a result of its reckless exploitation. This situation demands the application of scientific methods of culturing these eels. But, while the development of a suitable method for their aquaculture is inconceivable without a sound information of their biology, a survey of the literature on this topic showed that a very scanty information on the biological aspects of these commercially important teleosts is available so far. While Karim and Hossain (1972) worked on sexual maturity and fecundity of Mastacembelus pancalus, Srivastava (1975) reported the unusual development of the caudal fin of this fish. Sikdar and Das (1980) studied the skin structure of Mastacembelus armatus and Saxena et al. (1979) observed the cytological details of oocytes of this fish. Keeping in mind the paucity of information on the biology of Mastacembelus spp. in general, the present study was undertaken in order to find out the habitat and distribution of M. armatus , which is perhaps the most important of the four species of this genus found in India. It was also intended to find out the food and feeding habits of this fish, its length and weight relationships and breeding and rearing of its juveniles under controlled conditions. Attempts were also made to segregate the races of this species on the basis of morphometric and meristic characters in order to assess the growth potential of varied stocks. Studies on these lines 5 were thought necessary because without an adequate knowledge of food and feeding habits, growth, breeding and stock regeneration potential etc. of a fish its scientific cultivation is impossible. As pointed out by Panikkar (1952),it would be futile to manage fishery without the adequate knowledge of biology of the fishes concerned. Summary The work done on the biology of Indian freshwater fishes mainly deals with the carps, murrels and the cat fishes. But no attention has been paid to the study of the biology of the spiny eel, Mastacemhelus armatus (family: MastacemJbelidae) , which is palatable and nutritive. The spiny eels sold in the market are brought almost entirely from their natural population. In view of their dwindling natural population, the situation demands that scientific methods be applied for culturing these eels. But, development of a suitable method for their aquaculture is inconceivable without a sound knowledge of their biology. Keeping in mind the paucity of information on the biology of Mastacemhelus spp. in general, an attempt was made here to study the biology of M. armatus, which is the most important of the four species of the genus Mastacembelus found in India. 5^ I 1^ CHA?T£R - I Classification and cMofphologlcal Characteristics Classification and morphological characteristics An orderly grouping of organisms is essential because it provides direct and inferential informations about the nature of an animal. The body structure of an organism and its evolutionary history are two most important aspects of the study of classification from the ecological point of view because through them we can distinguish between the closely related species and ascertain their distribution in terms of different environmental conditions. Such a study also helps in determining the habitat and repeated association between two different species. As pointed out by Traverse (1984a), Mastacembelids belong to perhaps the most highly modified percomorph family, Mastacembelidae, and are entirely restricted to the freshwater. Their relationship with other percomorphs is unknown (Roberts, 1986,1989). They are called ,'spiny eels' due to their having a series of detached, depressible spines preceding the soft dorsal fin. A classification of the Mastacembelids was provided by Traverse (1984a). He puts the thirty three nominal of the freshwater spiny eels in four genera under two sub-families, namely Mastacembelmae and Afrornastacemhelinae. Of these, the species belonging to the genera Macrognathus and Mastace;7Lbelus of sub-family 7 Mastacembelmae are restricted to Asia while the genera of sub-family. Afrowastacembelinae are known to occur in Africa only. There are 11 species included in the genus Macrogmathus. Out of these only five species, namely, M. aral, M. caudiocellatus, M. zebrinus, M. pancalus and M. guntheri are found in India. The species of the genus Mastacembelus found in the Indian region are M. armatus, M. oatesii, M. alboguttatus and M. dayi. Out of these, the species M. alboguttatus and M. dayi are rare in occurrence. Of the remaining two species, M. oatesii attains a length of about 3.7 cm, and due to its small size it is of no interest to fisheries. Attaining a length of upto 65 cm, the species M. armatus is the largest spiny eel of them all. It is found in both plains as well as hills of India and is a very popular table fish. The systematic position of this species is as follows: Phyllum : Chordata Sub-phylum : Vertebrata Super class : Gnathostomata Class : Osteichthys Sub-class : Actinopterygii Order : Perciformes Sub-order : Mastacembeloidae Family : Mastacembelidae 8 Sub- family : Mastacembelinae Genus : Mastacembelus Species : armatus The species was described by Lecepede in 1800 as Macrognathus armatus (Hist, nat. Poiss, 2.286) later, Day (1878) named it as Mastacembelus armatus (Fishes of India: 340, pi. 73, fig. 2). Afterwards, Hora (1921) described it as Mastacembelus manipurensis (Rec. Indian Mus., 22:206, pi. 9, fig. 3) . It is now recognised by its name Mastacembelus armatus (Day 1876). This name has been accepted by Traverse (1984a). Common names : Tire-track spiny eel English Bami Assam ; Bam, Bami West Bengal ; Bami, Baam Bihar ; Bahm, Vahm, George Punjab ; Bummi, Gonti, Bahm Orissa ; Maudibommidai Andhra Pradesh ; Kalarah, Aaraah, shatarh Tamil Nadu ,- Mokkanarakan Kerala ; Vam, Vat Maharashtra ,• Baam U.P. Distinguishing characters: Different species of the same genus show slight but significant variations in their morphometric characters. These morphological changes can be studied easily for the purpose of identification. The variations shown by these species are due to the modif icat ional effects of the environment or they can be due to genetic changes. A brief account of the morphometric characteristics of Mastacembelus arrnatus has been given by Talwar & Jhingran (1991) , which is presented below : Body relatively slender. Preopercle with 2 or 3 spines usually conspicuous, but often one or more may be embedded in skin; preorbital spine strong and usually piercing skin. Mouth small, its gape 16.1 to 20.9% of length of head, extending below posterior nostril or at least to its anterior margin; sharp teeth in bands on both jaws. Spinous dorsal fin inserted above middle or posterior-third of pectoral fins, last dorsal spine small and hidden beneath skin. Dorsal and anal fins broadly joining to caudal fin. Vertebrae 79 or more. Colour: Rich brown and usually with zig-zag lines dorsally and laterally, some times anastomosed forming a network, but almost never extending upto abdomen; often a black band encircles the eye runs posteriorly from there describing an undulating pattern along the upper or dorsal half of the body; a row of black spots along base of soft dorsal fin and short black bands over the back under dorsal spines often present. Pectoral fins usually spotted; dorsal and anal fins usually banded or spotted. 10 Key to genera: 1. (a) Dorsal fin spines 32 or less; rostrum relatively large, in some species concave ventral surface lined with tooth plates; rim of tubular anterior nostril with six finger like projections; total vertebrae usually 84 or less Macroglia thus 2. (b) Dorsal fin spines 33 or more; rostrum relatively small,never concave ventrally or with rostal tooth plates;rim of anterior tubular nostril with two finger like projections and two broad-based flaps; total vertebrae 79 or more Mastacembelus Key to species: 1. (a) Dorsal and anal fins broadly joined to caudal fin; caudal fin outline merged with that of dorsal and anal fins; caudal fin rays 14 to 17 M. armatus (b) Dorsal and anal fins separate from caudal fin, or joined to 11 caudal fin only near its base. Caudal fin outline entirely or almost entirely separate from that of dorsal and anal fins; caudal fin rays 21 to 27 2 2. (a) Snout very broad and short jaws extending posteriorly fully two-thirds of distance to below anterior margin of eye;preopercle without spines,- body with a few large dark spots which may extend on to base of dorsal fin, fins otherwise plain M.oatesii (b) Snout very narrow and elongated ;jaws extending posteriorly half or less than half of distance to below anterior margin of eye; preopercle with 3 to 5 spines; body and fins with numerous pale round spots 3 3. (a) Body and fins with very numerous, small round pale spots without dark edges; body with numerous rings composed of 9 to 10 small pale spots 12 encircling a some what dark spot; caudal fin rays 21; vertebrae 82 Af. alJboguttatus (b) Body and fins with moderately numerous, relatively large, pale spots with dark edges; spot on fins around, but those on body often vertically elongated;caudal fin rays 25 to 2 7 ; vertebrae 85 or 86 AT. dayi Siimmary The spiny eels occur in tropical Africa and Asia only. In all there are thirty- three species of freshwater spiny eels which have been housed in four genera, two of which namely, Macrognathus and Mastacembelus are under sub-family Afromastace/njbelinae. Species of the genus Mastacembelus found in Indian region are M. armatus, M. oatesii, M. alboguttatus and M. dayi. Out of these, the species M. alboguttatus and M. dayi are rare in occurrence. As far the remaining two species, while M. oatesii attains a length of about 3.7 cm, and being of a small size is of no interest to fisheries, M. armatus attains a length up to 65 cm and is considered the largest spiny eel found in India. M. armatus is, therefore, of interest to fisheries, the more so because 13 it is considered to be very good table fish particularly in the plains of India where it is very popular especially when sold in live condition. 14 •Habitats and Distribution Habitat and distribution The spiny eels occur in India in a variety of freshwater habitats in the plains as well as in the hills. They are common in rivers, lakes, ponds, streams and estuaries. They have the habit of burrowing into the bottom and developing a unique niche in the sediment. In the fast flowing waters they often take shelter under the submerged stones. Some species of the spiny eels burrow in the substrate during the day time and come out at night for feeding. Mastacembelus armatus can stay buried in the substratum for several months, and has been recovered from 2the soil in drying ponds. Many of the spiny eels including M.arznatus are air-breathers and can survive in mud and oxygen deficient water for an indefinite period of time (Talwar and Jhingran, 1991) . Interestingly it is the tropical climate which is suitable for the biological needs of the spiny eels. Therefore, they occur in tropical Africa and Asia only. However, while the species belonging to the genera Mastacembelus and Macrognathus (sub family Mastacemhelinae) are restricted to Asia, members of the sub-family Afromasta- cembelinae are confined to Africa. This is because of the differences in physico-chemical and biological parameters 15 existing in these two continents which influence greatly the abundance and distribution of these animals. This tendency of spiny eels living in a narrow range of environmental conditions available in Africa and Asia only with their further segregation into two groups of genera with members of one group occurring exclusively in Africa and the other group being found in Asia, shows an evolutionary trend in this group of fishes. The spiny eel, M. armatus, inhabits freshwater and brackish water bodies in India, Pakistan, Sri Lanka, Nepal, Bangladesh, Myanmar through Thailand, Malaysia and southern China. Several inland water bodies in the northern and central states of India were surveyed for studying the species composition and distribution of the spiny eels. It was found that M. armatus is landed at Hardwar, Dehradun, Muzaffarnagar, Meerut, Bulandshahr, Aligarh, Mathura, Agra, Kanpur, Moradabad and Bareilly districts in Uttar Pradesh; Gaya, Patna, Jehanabad, Bhagalpur, Madhubani, Darbhanga, Muzaffarpur and Shaharsa districts in Bihar; Gurgaon in Haryana; Bastar, Hoshangabad, Itarsi and Chattisgarh regions in Madhya Pradesh; Howrah, Hooghly, Midnapore and Burdwan districts in West Bengal; and, in Delhi. It is also common in river Tawi (Jammu) and its tributaries at an altitude of 1200 meters. 16 Fishery informations M. arwatus is the largest Indian spiny eel known. In the present study it was generally found to be about 65 cm when fully grown. It is considered to be a very good table fish particularly in the plains of India. In West Bengal and western Uttar Pradesh it is very popular food fish especially when sold in live condition. SuHtmary The spiny eel, M. armatus, is restricted to Asia. It has been reported from Pakistan, Sri Lanka, Bangladesh, Myenmar through Thailand, Malaysia and southern China. It occurs in a variety of freshwater habitats in the plains as well as in the hills of India. It is common in rivers, lakes, ponds, streams and estuaries. The fish patrols a body of water throughout its length and breadth but spends major part of its life at the bottom of the water body. 17 CHA?T£R - in Stock Evaluation Introduction Identification of different stocks of fishes belonging to a single species is emerging as an interesting problem in the field of fishery management these days. There are reports of multiple stock composition of intraspecific fish populations (Radhakrishnan, 1957; Khumar and Siddiqui, 1992; Pepin and Carr, 1993). These various stocks have been observed to exhibit different patterns of body proportions in addition to showing appreciable differences in their reaction to environment and having different production potential. The identification of separate stocks in populations of commercially important fishes is of great importance to fishery biologists. Morphometric and meristic characters which are employed in identification and classification of fishes have also been used in segregating males and females among the fishes of given species, and for studying the relative growth and production of different stocks present among the members of a fish inhabiting the same or different water bodies. Knowledge of the relative growth of the discriminated stocks is helpful in judicial management of commercially important fish in aquaculture leading to higher yield. Radhakrishnan (1957) reported slight but significant 18 changes occurring in the morphometric measurements among the fishes of different stocks, races or populations. Several scientists (Pritchard, 1931; Hile, 1937; Godsil, 1948; Schefer, 1948; Marr, 1955; Royce, 1963; Krumholz and Cavanah, 1968; Fowler, 1970; Meng and Stocker, 1984; Fabrizio, 1987; Shaefer, 1991; Melvin et al., 1992 and Pepin and Carr, 19 93) have provided morphometric data on several species of fishes and emphasized their utility in separating stocks or races of the fishes living in different envirnment. Ichthyologists who have provided informations on the morphometric data of Indian fishes are Menon (1952), Pillay (1957), Tandon (1962), Gupta (1970), Chondar (1974, 1975), Hameed et al. (1977), Srivastava and Tyagi (1979), Dwivedi and Rattan (1980), Jayaram (1980), Acharya and Dwivedi (1984), Chowdhry and Dwivedi (1985), Piska (1990), Shah et al. (1991), Fatima (1991) and Khuumar and Siddiqui (1992). But, in India no one has related the discriminated stocks of a fish with their growth potential so far. In the present study, efforts were made to find out the stock composition of the riverine population of the spiny eel, M. armatus. The stock discrimination was done by studying a number of morphometric and meristic characters along with computation of the length weight relationship, and, the discriminated stocks were related with their respective growth potential. 19 Materials and Methods For the present study the specimens of the spiny eel, M. armatus, were caught from Kalinadi, a tributary of the Ganga river system. Each individual was patted dry, weighed and placed on a flat surface for the purpose of taking various measurements. While weighing was done to nearest 0.001 g using a sensitive electric balance, length was measured to nearest 0.1 mm. A fish measuring board was used for recording total and standard lengths. Other length and depth measurements were taken with the help of a fine pointed compass. All the measurements were taken along the right side of the body of the fishes. For morphometric studies the following characters were observed: Total Length Distance from the tip of the snout to the tip of the longest ray of caudal fin. Standard Length Distance from the tip of the snout to the posterior edge of the last scale along the lateral line. Head Length : Distance from the tip of the snout to the posterior most margin of sub- opercle. Snout Length Distance from the tip of the snout to the margin of preorbital bone. 20 Body Depth Distance between dorsal and ventral surfaces at the point of origin of the dorsal fin. Body Width Maximum width of the body at the point of origin of the dorsal fin. Orbit Diameter -. Distance between anterior and posterior margins of the orbit along the longitudinal plane Interorbital Width: Least distance between the two orbits. Caudal Fin Length : Distance from the posterior edge of last scale to the tip of the caudal fin. Caudal Fin Depth : Distance between the anterior and posterior margins of the caudal fin along the ventral plane. For the study of meristic characters the number of brachiostegal rays and dorsal spines were counted. Ratios of the parameters worked out were: Total Length/Body Depth; standard Length/Body Width; Standard Length/Head Length; Head Length/Snout Length; Standard Length/Orbit Diameter; Head Length/Interorbital Width; Caudal Fin Length/Caudal Fin Depth; and, Total Length/Body Weight. The proximity between different parameters was particularly observed and those showing a close range were categorised separately from those which diverged. The 21 coefficient of difference (CD) was computed by using the equation: Mx - My CD = SDx - SDy where, CD = Coefficient of difference between stocks Mx = Mean value of 'x' component of stock A My = Mean value of *Y' component of stock B SDx = Standard Deviation of 'x' component of stock A SDy = Standard Deviation of 'Y' component of stock B Weight per unit length (WPUL) and frequency of occurrence of each stock were calculated and compared with each other. In the case of stocks A and B measurements of the parameters Standard Length (SL), Head Length (HL), Snout Length (SnL), Caudal Fin Length (CFL), Predorsal Length (PL) , Body Depth (BD) , Body Width (BW) , Caudal Fin Depth (CFD), Interorbital Width (IW) and Optic Diameter (OD) were expressed in percentage of the total body length of fish (Table-2) . Further, for stocks A and B taking the above mentioned parameters as dependent variables, their regression over the total body length (taken here as independent variable) was also studied by the least square method (Table 2). Results of the computation of correlation existing between the above mentioned dependent variables and the total body length in the case of stocks A and B, are 22 also given in Table 2. The growth of the weight of fish relative to its length was examined by cube law. The analysis of length-weight data was done by using the logarithmic formula given by LeCren (1951): Log W = Log a + n Log L where, L = length in ram a = regression constant, and n = the slope Growth potential of each stock was calculated by dividing the mean body weight (g) of the fish of a stock with respective mean total length (cm) of the fish. Results Riverine population of the spiny eel, M. armatus, was found to contain two stocks which have been denoted here as stocks A and B. These stocks were sympatric and differed in a number of morphometric characters like the ratios of various body parameters (Table 1) . But the meristic data, such as the number of dorsal spines and brachiostegal rays, did not show any consistent pattern of variation. Maximum value of CD obtained here was 2.22 noticed in the case of SL/HL ratio. In the case of ratios HL/OD, HL/IW and HL/SnL, CD was 1.14, 1.18 and 1.15 respectively. These significant differences revealed that intraspecific variations existed among the specimens of M. armatus collected from river Ganga. Therefore, the multiracial composition of the 23 population of M. armatus can not be ruled out. However, stocks A and B were unevenly distributed in the population with frequency of occurrence being 37.12% for stock A and 62.88% for stock B. Comparative values of the body parameters for these two stocks together with their mutual statistical differences are presented in Table 1. Weight per unit length (WPUL) was 3.75 and 1.85 in stocks A and B respectively. The most striking inference obtained here is that these two stocks of fish which were sympatric and obviously exposed to similar environmental conditions and natural resources, differed with each other in their growth potential. Aquacultural importance of the stock discrimination lies in the fact that culture of the selected high yielding stock will give better production. The results of the analysis of regression of different body measurements (SL, HL, SnL, CFL, PL, BD, BW, CFD, IW and OD) on total length and the coefficient of their correlation have been given in Table 2 and Figs. 2A-2B. The values of regression coefficient computed for the above mentioned regression equations were found to be 0.96, 0.11, 0.04, 0.04, 0.11, 0.12, 0.07, 0.03, 0.02 and 0.03 for SL/TL, HL/TL, SnL/TL, CFL/TL, PL/TL, BD/TL, BW/TL, CFD/TL, IW/TL and OD/TL respectively for the individuals of stock A while their values were 0.89, 0.21, 0.04, 0.004, 0.12, 0.10, 0.08, 0.04, 0.02 and 0.02 respectively for all the members of stock B {Table 2) . It can be inferred from regression 24 analyses done here that the exponents of regression equations for all the dependent variables excepting those for HL/TL, PL/TL, CFD/TL and BD/TL are higher in the case of fish from stock A than those for fish from stock A. The mean values of head length, snout length, predorsal length, body depth, and body width for fish of stock A were 14.26% , 05.14% , 9.11% and 6.18% of mean total length respectively, while the mean lengths of those characters in the case of fishes of stock B were 10.54% , 04.97% , 14.51% , 8.34% and 5.52% respectively. Other characters did not differ significantly Figs. 3A-3B. The relationships between length and weight of the two stocks are as follows: Source Regression equation coefficient (r) Stock A Log W = -6.5158487+3.36088 Log 0.7102475 Stock B Log W = -5.5095236+2.9415228 Log 0.7803586 Discussion The form of a fish is the function of differential growth rates of its various body parts. Different organs maintain an allometric relationship with the overall body length and the strength of such relationship is responsible for normal body proportions. It has been noticed that either due to the genetic variation or phenotypic plasticity besides the influence of other factors, the population of a 25 species may include two or more stocks. In the present investigation, based on morphometric and meristic observations, population of the spiny eel, M. armatus, collected from Ganga river was found to have two stocks. Different workers have employed various tools for the purpose of stock discrimination. Some workers employed morphological and physiological characters for racial segregation (Mayer, 1942; Gupta, 1970) . Kesteven (1950) studied the ecological characters also. Pillay (1957) pointed out the utility of serological studies for this purpose. Pepin and Carr (1993) used DNA sequencing together with the morphological and meristic characters for stock discrimination of Gadus morhua. Genetic analysis is also an important tool for stock segregation because the degree of genetic sub-division among population ( measured according to Weir,1990 as '0' )is an indication of the extent to which animals sub-divided among different geographic areas exist as separate breeding populations (Wright,1951,-Weir, 1990). Several workers have reported the existence of intraspecific populations on the basis of morphometric and meristic characters. For example, Savvaitova (1963) found that specimens of Salvelinus alpinus collected from river differed from those obtained from lakes in a few morphometric characters also in addition to their differing in their feeding habits. Khumar and Siddiqui (1992) studied the morphometric and meristic characters of Puntius sarana 26 and on their basis segregated the specimens present in their collection into four independent stocks. Piska (1990) included length and weight studies along with morphometric and meristic observations for studying the specimens of Salmostoma clupeoides collected from two different reservoirs and reported insignificant differences between them except for differences in meristic counts of anal and caudal fins. In the present investigation morphometric, meristic, and length and weight characters were taken into consideration, but meristic data did not indicate any significant variation between the two stocks. Therefore, differentiation of the Ganga population of M. armatus was done here mainly on the basis of morphometric and length and weight characters. Being based on the morphometric, meristic and length-weight observations, the findings of the present study are similar in nature to the findings of those workers who have reported significant morphometric difference between different stocks of the population of a given fish. But, on the basis of this distinction alone and in the absence of studies regarding the genetic make-up of stocks, previous workers (Sawaitova, 1963; Ansari, 1982; Chatterji, 1976; Piska (1990) did not classify stocks present in the populations studied by them as separate stocks. In consonance with those workers the present author while indicating the presence of two stocks in the Ganga population of M. armatus, refrains from classifying them as 27 separate stocks. Straight lines were obtained after plotting the various morphometric measurements against the total length of M. armatus, indicating the linear relationship in each case. This showed that with the increase in total length of fish there was a corresponding increase in the length of various body parts. However, Godsil (1948) and Marr (1955) have observed a non-linear relationship between the measurements of various body parts and the total length of some other fish species, and emphasized that during the growth of fish the ratio between the measurements of various body parts and the length of the fish may not be constant. However, contrary to this, Chatterji (1976) obtained a linear relationship between different body measurements and total length. Khan (1972) reported linear relationship in the individuals of Labeo rohita attaining more than 50 mm length showing isometric growth. Similar results have also been noted by Chatterji et al. (1977a) in the case of Laheo bata and Hameed et al. (1977) in Labeo calbasu. The length- weight relationship of the individuals of both the stocks A and B did not deviate from the so-called cube law, indicating isometric growth of the fish. However, while stock A fishes grew more than the cube of the length, those of stock B grew less than the cube length. This indicates that the stock A individuals were more robust compared to the specimens of stock B. This finding was also confirmed 28 by the growth potential data of both these stocks. The weight per unit length (WPUL) was 3.75g in stock A and l.85g in stock B. Therefore, in the case of M. armatus the morphometric characters can be related with the growth potential for culturing the selected high yielding stock of this fish for maximum production. Simnnary The samples were collected from Kalinadi, a tributary of the river Ganga at Aligarh for stock analysis study. Various morphometric and meristic characters alongwith the study of length -weight relationship were used for stock discrimination. Riverine population of M. armatus was found to consist of two stocks which have been denoted here as stocks A and B. These stocks were sympatric and differed in a number of morphometric and meristic characters. The regression of different body measurements like standard length, head length, snout length, caudal fin length, predorsal length, body depth, body width, caudal fin depth, interorbital width and optic diameter on total length was studied. As a result of which, a linear relationship was noted to occure between them in the fishes of both the stocks. Correlation of coefficient in all the above mentioned relationships were highly significant. Various body proportions are expressed here as percentage of total length. Significant difference in the sets of characters, 29 head length/total length, standard length/total length, pre- dorsal length/total length, body depth/total length, body width/total length have been found between the fishes of stocks A and B. The equations obtained for length-weight relationships in the fishes of these two stocks were also different. Appreciable difference in growth of weight relative to length was notieable in these two stocks. Stock A which demonstrated faster growth (weight per unit length WPUL = 3.75g) occurred with 37.12% frequency, whereas stock B (WPUL =1.85 g) was more preponderant (62.88%). 30 Q. O o o o O o X- > ^ 30 -J 2 4- o o o H- C/3 2 n + 3 o m en o 2 o &J Q. 3 H- H- o o cn -a rn o o 3 o 4- U o 3 H- to m o 3 o 2 r o n o 3 o m o o H 3 3' to o O as H- o H- o 3 o a- O H- cn m -I to O n o 00 —00» 2 •n n H- T1 I+- O re O o 3 b O H- to (/5 O _^ m on 3 o o 1—1 •(>• o H- H- C/3 o "^ O o in r CO s3^ H- O (/5 w -o to OJ to H- H- 2 O r o ^ b 3 b H- m o iji 00 b Ul 00 5 o ON o 2 "a. H- re 3 o 3 Crt H- C/3 m Z fB •-< o OS 3 o to f+- H- ON o H- cn o rn Table - 2 Relationships between different body measurements (Y.cm) on total length (X,cm) of stocks A and B in M. armatus Body Mean Mean Regression equations Correlation Percent "f Remark; chara- Length total of body measurements coefficent of total (5%) ter body length Y = a + b X "r' length measur. (cm) (cm) Stock - A SL 35.15 + 1.2467 36.5 Y = 0.073622 + 0.9612X 0.83268 98.95 10.31 S HL 06.03+1.2831 36.5 Y = 2.16663+0.10579X 0.6337982 14.26 5.62 S SnL 01.84+1.2185 36.5 Y = 0.1091+0.0473X 0.749182 05.14 7.75 S PL 03.91±1.2423 36.5 Y =-0 .24163 + 0.1145X 0.9033864 10.54 17.26 S CFL 01.68^1.1451 36.5 Y =-0.1433 + 0.0467X 0.929349 04.74 14.45 S CFD 01.63±1.1924 36.5 Y = 0.3343+0.0345X 0.8274112 04.63 6.55 S BD 03.94±1.1924 36.5 Y =-0.511 + 0.122X 0.690648 09.12 10.72 S BW 02.25+1.3227 36.5 Y =-0.154+0.718X 0.842368 06.185 10.10 S IW 0.72^1.2134 36.5 Y =-0.125 + 0.0255X 0.677423 01.28 6.32 S OD 0.65+1.1720 36.5 Y =-0.233+0.0342X 0.736424 01.18 7.47 S Stock - B SL 23.4±1.242 26 Y = 0.156321 + 0.89534IX 0.9939578 98.38 81.49 S HL 05.67 + 1.018 26 Y = 0 .3543 + 0.637168X 0.637168 12.75 7.44 S SnL 01.19^1.3295 26 Y = 0.0862+0.720939X 0.720939 04.97 S.36 S PL 03.71i^l.24S 26 Y = 0.5251 + 0.90999X 0.90999 14.51 19.75 S CFL 01.27+1.3362 26 Y = 0.0325 + 0.919037X 0.919037 04.85 2C.9t S CFD 01.36j;1.235 26 Y = 0. 1332 + 0. 9038124X 0.9038124 04.27 16.99 S BD 02.68^1.299 26 Y = 0.042+0.883679X 0.883679 08.34 21.55 S BW 01.36^.1.387 26 Y = - 0.819 + 0. 92275X 0.92275 05.53 19.C: S IW 0.39^1.207 26 Y =-0.153+0.724296X 0.7242296 01.33 9.45 S OD C.35+1.156 26 Y =-0.177+0.735524X 0.735524 01.27917 9.77 5 00 u js >£ M) -w £ MM t c a re - ^ J - t ^ ^ fi « = c 5 c >-. s •=«s s .2 fc fa^ S- •o J « s: J -^ fi "« IS " c _ -o c _ .c « o "o ~ H.i •O T5 >^ V. - « « « o 3 3 TJ 3 o 5 2 « c c R R e C H c^ ft. E (/I C U U PC c E ^M(^Tt«r, vci^ocoN u 3 M r^ rr Fig. 2. Regressions of different body measurements on total length of M.armatus. 2A. Stock A; 2B. Stocl( B. Totil length 16 20 2E 30 36 40 46 60 66 60 Different body measurements 8L HL SnL BD CFD CFL BW IW ZA Total length 70 60 - y'' 60 " 40 ~ y^ 30 ^X 20 ^ y^^ 10 1 1 1 1 r '• 10 16 20 26 30 36 40 46 60 66 60 6E Different body measurements 8L HL SnL BD CFD CFL BW IW 2B Fig.3. Different body measurements expressed as %age of mean total leng of M.armatus.3A.Stock A;3B.Stocks %a0e of total length 120 1 100 SL HL SnL PL CFL CFD BD BW IW OW Different body characters 8A %a0« of total length 120 100 SL HL SnL PL CFL CFD BD BW IW OW Different body characters 3B Ci-IA?T£R - IV !Jood and ^ceding IHablts Introduction The importance of a thorough study of the functional morphology and anatomy of the organs of a fish concerned with feeding and digestion of its food is well established in the investigations of fishery biology. The organs concerned with feeding generally exhibit some very outstanding examples of structural adaptations correlated with feeding habits. Through such a study the feeding habits of both adult and juvenile stages of fish can be well understood. Therefore, the study of alimentation of a fish is necessary while investigating its food and feeding habits. The food of fishes includes both the dissolved nutrients as well as the bodies of a whole range of plants and animals. As for the food dissolved in solution, many essential and non essential compounds and ions present in water are either absorbed directly through the gills or are swallowed along with the food and are then absorbed in the digestive tract. For example, extra enteral absorption exists for calcium which is vital to fish for scale and bone formation (Lagler, 1962) . Fishes differ greatly in the character of food which they consume. The natural food of fishes can be classified 31 under three groups, (a) 'main food' or the natural food which the fish prefers under favourable conditions and on which it thrives best, (b) 'occasional food' or the natural food that is well liked by fish and is consumed as and when available, and (c) 'emergency food' which is ingested when the preferred food items are not available and on which the fish is able to survive barely (Schaeperclaus, 1933) . Feeding habits of adult fish vary according to the amount and type of food present in a particular environment. The food spectrum of a fish can also differ with season. While herbivores and carnivores are reported to show a definite peak period in their feeding during the year, omnivores show little variation in their feeding throughout the year (Das and Moitra, 1955a). The study of the trophic biology of fishes had started since the beginning of present century (Raj, 1917; Hornell, 1924; Hornell and Nayudu, 1924) . This was in view of the importance of food and feeding habits as an environmental factor influencing the growth, distribution and migration of fishes and the success of their fishery. Thus the knowledge of food and feeding habits is essential for proper management and exploitation of fishes like, for example, the pond cultivation of economically important fish species. A study of the structural adaptations of the organs concerned v^ : th feeding is useful for understanding the feeding hat" ts of fishes. But inspite of a good amount of 32 published data available on the trophic biology of freshwater fishes in India, very little information is available on the structural adaptations of their feeding organs. Among those who have given any information on the correlation between feeding organs of a fish and its feeding habits are Al-Hussaini (1945,1949) Bapat and Bal (1950), Mookherjee and Ganguly (1951), Pillay (1953), Kapoor et al. Sinha (1975), Mishra et al. (1991), Fatima (1991) and Oja and Singh (1992) . A survey of the literature shows that quite a good amount of work has been done on the biology of fishes with special reference to food and feeding habits of different types of freshwater fishes, notable references in this connection being those of Khan (1934), Mookherjee et al. (1947), Karamchandani et al. (1967), Khan and Siddiqui (1973), Jafri and Mustafa (1975), Mustafa (1976), Chatterji et al. (1977c), Aravindan (1980), Tandel et al. (1986), Khan (1988), Reddy and Shanbhogue (1988), Wijeyaratne and Costa (1988), Dasgupta (1990), Dutta and Malhotra (1990), Rao and Rao (1991), Ojha and Singh (1992), Dutta (1993) and Khan and Fatima (1994) . But very little work has been carried out so far on the trophic biology of the spiny eels. The present study focuses on the food and feeding habits of M. armatus with special reference to the functional morphology of its feeding organs and their structural modifications in relation to intake and consumption of food items. 33 Materials and Methods Specimens which formed the basis of this study were collected from ponds and rivers in and around Aligarh district using cast and drag nets. Fish were sampled on monthly basis. The samples were taken in the morning so as to minimize the possible effect of diet on feeding and differential digestion of food items. Moreover, at this time of the day the guts were found to be full of food organisms which were still fresh and could be easily identified. Total length of the spiny eels was measured from tip of the snout to longest caudal fin ray upto nearest 0.1 mm. Their weight (g) was recorded on an electric balance sensitive upto nearest 0.001 g. Males and females were separated and divided into five length groups of 10 cm intervals. Since it was not possible to observe the eels while they were feeding, an assessment of their food and feeding habits could be done only indirectly through the analysis of their gut contents. For this purpose the freshly caught specimens were cut open in the field and their guts were removed and preserved in 10% formalin and brought to the laboratory for further investigations. The dentition, and the structural details of different parts of digestive tube of these eels were sketched and photographed. Relative gut index [length of alimentary canal X 100/total length of fish (cm)] was worked out. Strength of relationship between the 34 gut length and the total length was expressed here by computing correlation coefficient 'r'. Regression of the gut length on the total body length was computed by using the formula. Log Y = log a + b Log X It has been established in the case of certain fishes that there is a lessening in the intensity of feeding in them during their spawning season followed by a remarkable acceleration in their feeding activity after spawning. To ascertain such facts the condition of gonad was examined and the state of maturation of a fish was determined following the scheme of classification used by Qayyum & Qasim (1964a) for Ophiocephalus punctatus. The number of fish with full, medium and empty guts collected in each month was expressed as a percentage of the total number of specimens examined in that month. This was done for the purpose of determining the feeding intensity as suggested by Khan et al. (1988). Gastrosomatic index (GSI) was calculated by using the equation. Weight of gut containing food items (g) GSI = X 100 Weight of fish (g) As summarised by Lagler, 1956, various methods have been employed by fish biologists in the analysis of gut contents. Job (1940) followed the 'volumetric method'. Eye-assessment method was used by Bapat and Lai (1950) for various food items of some inshore fishes. Hynes (1950) 35 studied the stomach Gontents of freshwater stickle backs by the number method. Pillay (1952) suggested that the method to be adopted should depend on the particular diet of fish. 'The index of preponderence' method of Natrayan and Jhingran (1962), which was adopted by James (1967) for ribbon fishes, was found to be apparently suitable for carnivorous fish feeding on such food items as small fishes, shrimps and prawns, mysid and crustacean larvae. However, methods like the frequency of occurrence (number of guts containg a particular type of food item x 100/total number of guts examined); numerical count (number of various types of food items in a gut x lOO/total number of food items in the same gut); and , gravimetric method (weight of each type of food item in the gut in g x lOO/total weight of all the food items in the gut, g) were applied here. Qualitative analysis forms an important part of gut content analysis,- and, it was on the basis of a qualitative analysis that all quantitative assessment were made here. For this purpose the prey items were identified and categorised according to their systematic status. Results Morphology and anatomy of the organs concerned with feeding and digestion In M. armatus the organs concerned with feeding and 36 digestion are modified according to its versatile feeding habits (Figs. 1,2,&3). In the course of this study both kopfdarm (comprising buccal cavity and pharynx) and rumpfdarm (comprising foregut which includes esophagus and stomach, midgut which includes the intestine and hindgut which is represented by the rectum) were examined. In this fish the mouth is equipped with fine but firm jaws. The upper jaw is longer than the lower jaw and, therefore, projects over it. The pointed mouth perhaps facilitates probing of the food items which are concealed under submerged objects and bottom deposits. There are numerous small but strong pointed and backwardly directed sharp villiform teeth present on the jaws and in the buccopharyngeal region. The nature of dentition suggests that the teeth are meant for grasping and holding the active prey and preventing it from escaping. The absence of gill rakers appear to have been compensated by higher efficiency of dentition in performing the function that is normally assigned to the tooth like gill rakers in predatory fishes. In place of gill rakers an uneven gill arch surface is present in M. armatus. The pointed teeth, all of which are not of uniform size, (Figs.2-3) are present in large number to immobilize the ingested organism which is generally swallowed whole with no mastication taking place in the mouth cavity. This fish lacks such structural adaptations as are required to consume those items which need grinding 37 and mastication in the oral cavity. This perhaps accounts for the absence of molluscan shells in the gut contents of M. armatus. It has, however, resulted into an specialization in feeding on particular types of food. The mouth gap is wide enough to permit the intake of small to mediu sized shrimps upto 8 or 9 cm in lenght . The buccopharyngial cavity is equally accomodating. The mouth with a long gap obviously contributes to broadening the dietary spectrum of this fish. The buccopharyngeal cavity leads into a thick walled short and tubular esophagus which in turn leads into a well developed and elongated stomach which has thick and muscular walls. Internal lining of stomach is wavy. The structural modifications of stomach allow the stomach to perform its mechanical function of macerating the food in addition to working as a significant site for digestion. It is here that the food is stored, macerated, reduced to bits and subjected to digestive hydrolysis. The secretions of stomach, especially the hydrochloric acid, serve to kill the live prey. The remarkable distensibility of stomach indicates this organ's capacity to receive even the relatively large sized food items. In the absence of mastication taking place in the buccopharyngeal cavity, the ability of the stomach to deal with prey organisms assumes importance. A large sized spiny eel appears to display extreme predation and shows preference for bigger prey organisms in order to 38 obtain greater quantum of energy in a single foraging effort. The support rendered by the stomach in reorientational spectrum and feeding strategy is of pivotal significance. Stomach opens into the intestine which is thick walled and almost straight. In length the intestine is about one third that of the total body length. The intestine length/body length ratio was found here to be 0.27-0.34 (mean 0.31). Intestine constitutes less than half (48.97+_ 1.8 SE) of the total length of the alimentary canal in this fish. The distal portion of hindgut is filled with faecal matter and constitutes rectum. It is short and its diameter varies little from the intestine. Relative gut index Relative gut indices of the spiny eel are given in Table 1 and Fig. 4. Absence of any appreciable difference in this index in juvenile and adult fish indicates that the growth does not involve any major shift in their basically carnivorous orientation of the dietary habit. In the present study gut length/body length ratio in specimens of different sizes varied from 1:0.50 - 1:0.68. Interestingly, this variation was noticed in both young as well as adult fish, thus ruling out any substantial changeover in their diet. In view of the consistency in the gut length/body length ratio over the entire size range of fish inclusive of both juveniles and adults, it was found possible to express 39 the relationship between gut length and body length through the equation: Log gut length = - 0.27882 + 1.0477 Log body length (cm). There existed a significant correlation between gut length and body length. The value of correlation coefficient 'r' was 0.943 {p<001). Intensity of feeding in relation to seasons The values of gastrosomatic index (GSI) for different months are given in Table 3 and Fig. 6. It was found that the individual in the size range 21-50 cm consumed more food during summer than during rainy season and winter. The younger specimens (5-20 cm) were found to be feeding heavily during the post monsoon and autumn periods. Like adults, however, they too consumed lesser quantity of food during winter. While pronounced feeding activity in the younger individuals of both sexes was observed in the month of October, it was extremely low in the month of December. In adult female specimens a higher value of gastrosomatic index for all sizes was recorded in the month of April; but, in these cases the low values of gastrosomatic index varied with size, and while the lowest value for the size group 31- 40 cm it was observed in August and for those in the size range of 41-50 cm it was noted in October. Maximum number of empty guts were found during spawning and during winter season. 40 Feeding intensity in relation to maturity stages Table 2 and Fig. 5 indicate feeding intensity in males and females at different stages of their maturation. An increase in feeding intensity was observed in the ripening stage (iii) as the fish approached the size at first maturation. However, it was comparatively reduced in the riped stage. Maximum number of empty guts were encountered in both males and females of this stage. Higher percentage of medium fullness was recorded in the maturing stage (II) of male individuals and the immature stage of females. Food composition The diet of the spiny eel could be divided into a number of categories (Table 4-5) . Freshwater shrimps {Macrobrachium spp.) were the most preferred prey organisms. Other organisms consumed were dipteran larvae, brine shrimps (Branchipus spp) , earthworms and minor carps depending on the frequency of their occurrence. The food categories of lesser importance were aquatic vegetation, fish eggs and barbies which appeared to have been accidentally swallowed by the fish while it was voraciously feeding on other food organisms. Following the criteria proposed by Nikolosky (1963), food of the spiny eel could be divided into three categories on the basis of the relative nutritional importance of different component. Of major importance to the fish were the basic food categories which consisted of 41 items normally constituting a large part -of the gut content. Those present in relatively smaller amounts belonged to the secondary category, while the items that occurred rarely in the gut foirmed the tertiary or incidental food category. In the case of the spiny eel, the crustaceans and forage fish were basic food of the adults (Table 5 and Fig. 7) , while annelids and aquatic insects constituted the basic food of the juveniles. Annelids and insect larvae could be considered as the secondary food for adults, while forage fish and crustaceans together represented the secondary food of juveniles. Molluscs and aquatic vegetation could be regarded as incidental items for both juveniles as well as adults. Discussion A very close correspondence was observed between the food and feeding habits of M. armatus and the morphological features of its alimentary tract. The shape of its body and mouth, the dentition present in the mouth, absence of gill rakers, a well developed and strongly built stomach, a short intestine together with the dominance of animal matter in the gut contents described its carnivorous and active predatory habits. Body width in all life stages of M. armatus was about 5.56% of total body length resulting into slender body. This also pointed towards its agile life style which suited its predatory nature. Body width and 42 total length were found to have a significant correlation (0.9227656). Gill rakers which are instrumental in sieving plankton from water, have been found to be present in the herbivorous carps. Their role in the feeding behaviour of carps has been described by Sinha and Moitra (1976) and Marsh (1987) . Sinha (1986) reported changes in the number and structure of gill rakers between young and adult estuarine cat fish, Plotosus canius. In the present study, gill rakers were found to be absent in the spiny eels. Absence of gill rakers and the presence of a short intestine not suited to extracting nutrients from low digestibility phytoplankton, rule out the possibility to this fish being phyto-phagous animal. Several workers (Khan, 1972; Sinha and Moitra, 1976; Khan et al., 1988) have explained the correlation between gut length/body length ratio of fish and the nature of its diet. In the present study, while no remarkable difference in this ratio was observed between juveniles and adults of M. armatus, difference was, however, noted between the diet of young and adult specimens. But this difference was more of a systemic nature and fell short of diverging from the carnivorous habit of this fish. Similar observations have been reported by Khan et al. (1988) in Mystus neinurus. But Das and Moitra (1958) reported a remarkable 15,00% increase in the gut length/body length ratio in the grass carp, Ctenopharyngodon idella, during its growth from fingerling to adult stage. The 43 gastrosomatic index of a fish is generally used as a reflection of the intensity of its feeding (De Silva and Wijeyaratne, 1977). Seasonal variations in the gastrosomatic index of M. armatus indicate that this species does not feed at the same rate throughout the year. A noticeable reduction in its feeding intensity was denoted by occurrence of a large number of empty guts or those guts which contained traces of food material in them in the specimens collected during the lean feeding period. The findings of the present study left no doubt that the foraging activity of this fish fluctuated during the rainy season, which is also the high time for it to spawn. The intensity of feeding declined when the fish became ripe and was ready for spawning. Intrinsic factor in the form of the stress brought to bear on the alimentary canal of the fish by its developed gonads appeared to be the causative factor in the decline in its feeding. The occurrence of low feeding in other fishes coinciding with their peak breeding has been noticed by several workers (Jhingran, 1961; Desai, 1970; Bhatnagar and Karamchandani, 1970; Wijeyaratne and Costa, 1988a, 1988b; Khan et al., 1988). Low intensity of feeding in adults of M. armatus was also recorded in some other months such as August and December. The low feeding rate in these months may be due to some factors other than breeding. Like it may be due to the non-availabilit\- of food organisms in the environment and the effect of certain 44 abiotic factors such as temperature and turbidity. All age groups of the spiny eels including the very young ones were found to consume minimum quantity of food when water temperature was at its lowest. Reduced food intake in low temperature conditions during winter months has been shown in many other species of fishes including the major carps (Vashist, 1960). Contrary to this, however, Qayyum and Qasim (1964) reported high feeding intensity in Barbus stigma during winter, and emphasised that the low temperature and ripe gonads do not affect the feeding rhythm of that fish probably due to its omnivorous habit. But in M. armatus the intrinsic factors in the form of low appetite and requirement of low energy for maintenance of the fish may be the causative factors for its low intensity of feeding during winter. The high rate of feeding in younger and spent individuals during the post monsoon period may be due to high requirement of food for growth and development in immature fish and building up of gonads in the case of spent fishes. This is so because during this time the spent ovaries recover whereas the virgins start maturing. The presence of higher number of empty guts in the gravid females and ripe males is due to low intensity of feeding in their case during breeding season. In ripe fishes the space inside the body cavity got reduced because of the growth of the reproductive organs and the digestive 45 organs were pushed towards the dorsal side. As indicated above,these factors may be the reason for the low intensity of feeding in the ripe stage. Fish with medium gut fullness were encountered in almost all the months. This suggested that feeding never discontinued and even during the breeding season there was no cessation of food intake. It is interesting to note that in both sexes the most active feeding period was found in the ripening stage which is the third stage of sexual cycle. This suggests that at this stage the fish feed more voraciously because of a higher demand of food for the building up of gonads. Khan et al. (1988) also reported the same type of feeding intensity in relation to the stages of maturity in the freshwater cat fish, Mystus nemurus. But, working on Pampus argentius, Kuthalingam (1967) recorded an increased feeding intensity during the early stage of maturity including the immature and maturing stages of that fish and reduced intensity in its members with mature gonads. Table 4-5 indicates beyond doubt that the diet of M. armatus mainly includes animals and their body parts. Therefore, M. armatus may be referred to as a carnivorous fish. Presence of large number of prawns and forage fishes in the gut of adult M. armatus indicates that the fish prefers large sized food items. Selective feeding can be expected from the fish when the energy gained by it by feeding on preferred food items exceeds the energy lost in the efforts which the fish makes in capturing its 46 food. Many authors reported that in general fish spends much of its energy in selecting and capturing the prey of large size in order to get more energy (Hinde, 1958) . However, this view has been disputed by Cramer and Marzolf (1970). In the present study complete avoidance by it of plant oriented substances and greater dependence on large sized animals of prey, particularly fishes, show that M. armatus looks for the food which is easily & readily digestible in order to achieve maximum assimilation in the body. Earlier, Allen (1941), Thomas (1962) and Maitland (1965) have also found that the larger the size of the fish, the larger is the food item taken by it. The present investigations further indicate that despite the occurrence of different types of animals in the habitat, M. armatus selected only a few of them 'stenophagism' as exhibited by M. armatus seems to include the crustaceans and forage fishes in the case of adult M. armatus and annelids and aquatic insects in the case of juveniles. Qayyum and Qasim (1964) while studying the food of Ophicephalus punctatus also found that there were differences in food preferences of its various age groups. Tamubi Devi et al. (1992) studied food of Rita rita and reported that small sized fish consumed more crustaceans than the larger fish. This observation in Rita rita is contrary to the present observations, where compared to the juveniles the larger sized fish consumed more crustaceans. The present findings 47 that the larger specimens of M. armatus consumed comparatively more prey fish than its smaller sized individuals is similar to the findings of Anwar and Siddiqui (1992) in the case of the cat fishes. Summary The spiny eel, M. armatus is highly predacious in nature and prefers live aquatic crustaceans and insects as their food. Well developed dentition, strongly built stomach and short intestine are some of the characteristics which were related to the fish's dietary composition. M. armatus has an uneven gill arch surface in place of gill rakers. There was no major shift from a basically carnivorous orientation in the feeding activity of this fish during its various stages of growth. Gut contents analysis showed that macro-crusceans (especially shrimps) and forage fish were the main food of the adults while annelids and aquatic insects were taken by the young specimens. Molluscs and aquatic vegetation were consumed as incidental items. Gut length/ body length ratio of the fish varied from 1:0.50 to 1:0.68, foraging activity fluctuated with season. Feeding intensity was high in early maturity stages and was got relatively lower in fish with ripe gonads. Adult specimens consumed more food in summer than winter and rainy season. Food intake in younger specimens was greater in post-monsoon period and autumn, but pronounced feeding 48 activity was oberved in the month of October. Extremely low feeding was observed in the month of December. In adults maximum number of empty guts were found during spawning and in winter. 49 Table - 1 Relative gut index of M. armatus of different sizes Total length Of fish No. of Relative gut index (cm) observations 5-10 19 0.50 + 0.021 11 - 20 08 0.56 ± 0.024 21 - 30 10 0.68 + 0.026 31 - 40 49 0.64 ± 0.005 41 - 50 24 0.63 + 0.006 Table - 2 Feeding intensity of the Af. armatus in different stages of maturation Maturity Males Females Stages Empty Medium Full Empty Medium Fu guts(%) fullness(%) (%) guts(%) fullness(%) {% I 55 28 17 53 34 13 II 50 30 20 53 31 16 III 48 12 40 50 12 38 IV & V 60 22 18 65 20 15 2 S o 2 3+ 3 3 S- 3 I 3- i ,| 3 m ^ -1 -t -n n H- — — K) yj ' 3 ^ ~J 00 4^ — 0\ 'v^ i-n 00 00 ro — o o 4- — p p •-' O P (>J 00 so O 00 00 O Lft O K> o 3 Q 3 g- 5' O K) K> ' ' + — 00 — OS Q. 00 ^ 00 Ov ^ U> H- N> — — K>S)hJIOK>K)tsJhOS>K> -J »0 -^ i-rt bN U) <~n b^ U) (^ ho k> Rp O -n 00 re 3 o Si H- S) ^ — hO|rOK>K> — MK)hO—.— -T1 o o __ ^JOOvl-^JONLAsOUfV-^OO^OO 3 O 00 o 3 ^f M 00 O b\ b\ i-ft 4^ 4^ L/i -tk K> K> — o 3 H- w a. P '^ b\ ^J b\ l^ •— sO 00 ^ b^ Ln — N> H O S>K)U)tOK>KJUIU)LJU)LO'.^ O Ln 00 NJ O bs OO k> i-^ iyi 4»- k) k) ?0 3 K> I 3 2 TO TO H- w n 9, vO vo —• S> Ln ^ Lft Cv i-n *^ l/i 4^ en TO 3 H- K) P -J *>. bs >0 00 so 4»- O 00 i>J bv KJ bv 3 o H- to -n o n ^ o i>j bo ON 00 ^ ui bo -^ ID sO as o o 3 n o -J bv SO O —1 00 >0 -t^ i-t 4^ —• •{»• b> o H- o iyi ^ o >o ^- b\ 00 b\ L« SO 00 ON to H- « U) H- •-• — K> KJ U» U) K> K> — p -J Gut contents of the spiny eel,M. armatus Food Items Numerical Frequency of Gravimetric count ocurrence index (%) (%) (%) 1.. Cxrustacea Macrobrachium 82 55.7 97.52 Eubranchipus 25 28.8 0.97 Daphnia 18 11.5 2. Teleostomi Punt 2 us 14 23.0 27.52 Esowus 08 07.6 09.57 Osteochilus 04 05.7 12.32 imidentifled 25 48.0 62.20 Scale 40 38.4 0.98 3. Aquatic insects (Larval Stage) Ephemeroptera Numerous 19.2 6.80 Diptera Numerous 30.7 8.52 Hemiptera 02 05.7 0.43 Unidentified 30 11.5 2.32 4. Annelids Earthworm Numerous 26.9 15.00 5. Mollusca Gastropods 05 03.8 0.21 6. Digested matter 36.5 35.00 7. Aquatic vegetation 03.8 04.32 8. Fish eggs Numerous 07.6 02.35 9. Barbels 40 17.3 0.53 Table - 5 Percentage con^osition of broad categories of food items of Af. armatus Food items Young Adult (5 - 20 cm) (21 - 50 cm) Teleostomi 05 18 Crustacea 15 38 Aquatic insects 30 14 Annelids 34 15 Digested matter 13 12 Aquatic vegetation 01 03 Fig. 1. Alimentary canal of M. armatus. A. Liver (side view); B. without Liver (side view) Fig. 2. Dentition of M. armatus. Jaws with teeth (side and surface view) Fig. 3. Dentition of M. armatus. Buccopharyngeal teeth (surface view) K^Kf Fig. 4 Relative gut index of M.armatus of different sizes Relative gut index 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 5-10 11-20 21-30 31-40 41-50 Total length of fish(cm) Fig. 6 Variations in the intensity of feeding with maturity stages of M.armatus Gut fullness(%) 70 60 50 40 I 30 li 20 'IS 10 v^ A- ' 0 II III IV & V Maturity stages Empty guts(%) Medium fullness(%) Full(%) Males Gut fullness(%) 70 60 50 40 30 20 10 I II III IV & V Maturity stages ^^ Empty guts(%) ^ Medium fullness(%) Full(%) Females Fig. 6 Seasonal variations of gastrosomatic index with respect to size in M. armatus Gastrosomatic index 1 i i' y- > • y- i / • >" / • 5" y V" I y I, >" y y > • 5 ' y. y y' : >y .• f : i J; ii. JAN. FEB. MAR. APR. MAY. JUN. JUL. AUG. SEP. OCT. NOV. DEC. Months ^ 6-10 l_y 11-20 21-30 ^ 31-40 USD 41-60 Fig. 7 Percentage composition of food of M.armatus Percentage of food items 40 30 ^ w w 20 10 0 Teleost. Crust. Aq. Ins. Annl. Digd.matt. Aq.Veg. Foods items Young (5-20 cm) Adult (21-50 cm) JI-ength-'AVGlght Relationships Introduction In the study of biology of a fish it is important to compute the mathematical relationship between the length of the fish and its body weight. This relationship is possible because weight of the fish is a function of its length. Since the body proportions of a fish continually change with age, information regarding its length-weight relationship is useful in several ways such as gaining an idea regarding the general well-being of the fish in a given environment, studying variations in growth, determination of stock difference, estimation of instantaneous mortality rate and establishment and regulation of fisheries and fish yield. This relationship is also related with its life history stages such as metamorphosis, size at first maturity, gonad development, spawning and breeding season. Statistically the weight of a fish can be calculated with the use of derived length-weight equation for a given length of fish or vice versa. Estimated length of the marketable size of a fish of derived weight can be used for the preparation of corresponding size of mesh for better catch per unit effort. The length-weight relationship of the Indian freshwater fishes has been studied by many workers (Khan and Hussain, 1941; Jhingran, 1952; Sinha, 1972; Marichamy, 1974; Vmci et 50 al., 1974; Chatterji et al. , 1977b; Mustafa, 1978, Soni and Kathal, 1979; Malhotra, 1982; Lazarus and Reddy, 1986; Gowda et al. , 1987; Khumar and Siddiqui, 1991; Zofair and Mustafa, 1991) . But no work on this aspect of the biology of M. armatus has been done so far. Therefore, an attempt was made here to study the length-weight relationship in the fish. Materials and Methods About 214 live specimens of M. armatus (size range 18- 48.2 cm ) were captured with the help of cast and drag nets from river system in and around Aligarh district. They were brought to the laboratory where a total of 162 adult and 52 juvenile individuals of this fish were measured for their total length from the tip of the snout to the end of the caudal fin upto the nearest 1 mm, and weighed by a single pan balance sensitive up to 0.001 g. The adult fishes were sexed and separated into two groups, males and females. Juveniles were treated separately. The length-weight relationship was estimated by the method of least squares using the parabolic equation of the form W = aL^ as suggested by LeCren (1951), where, W = body weight in g 51 L = total length in mm a = constant and b = exponent Applying logarithms to the equation, it could be expressed as: Log W = Log a + b Log L where, Log 'a' and 'b' are constants. Constant 'a' measures the initial growth index and 'b' represents the slope of the regression line. Values of these constants were calculated by the least square method and then transformed to logarithmic equation. The correlation coefficient was determined by the equation given by Michael (1984). In order to find out the differences existing in length- weight relationship of males, females and juveniles covariance was employed. Results The logarithmic regression equations obtained for juveniles, males, and females as well as the equation for the combined data of males & females are as follows: Juveniles : Log W = -6.1307+3.3695 Log L Males : Log W = -5.84910+3.09113 Log L Females : Log W = -7.10649+3.60328 Log L Combined : Log W - -6.35371+3.295581 Log L (Male & Female) 52 The corresponding parabolic equations may be represented as follows: Juveniles : W = 7.401 x 10°"^ L3.3695 Males : W = 1.415 X 10°^ L^-^^^^^ Females : W = 7.8 x 10"°^ L^-°^328 Combined : W = 4.4 x lO'^"^ L3.29558 (Male & Female) The correlation coefficients for these relationships were found to be 0.9763, 0.971159 and 0.976362 for juveniles, males and females respectively. These values of 'r' were highly significant at p<0.001. The details of these regression and correlation studies are given in Table 1 and Fig. 1. In the case of juveniles, males as well as females the value of exponent was found to be more than the cube of standard length but the rate of increase in weight in relation to length (regression coefficient) was slightly higher in the case of juveniles (3.3695) than in males and females combined ('b' = 3.295581). Among males and females, however, it was higher in females ('b'= 3.60328) than in males ('b' = 3.09113). The comparatively high values of 'b' for juveniles and females indicate high growth rate in them compared to males. The high value of 'b' in juveniles may be attributed to their high feeding intensity and in females it may be due to the enormous growth of ovaries in them. The significance of variation in the estimates of coefficient 'b' from expected cube law was tested by a 't' test. The values obtained for juveniles, males and females 53 were 29.9023, 41.3374 and 33.5006 respectively, which are highly significant at 5% level. Analysis of covariance for ascertaining the difference in the regression lines of the length-weight relationship obtained for males and females of M. armatus shows significant difference between their slopes (5.44,d.f.1,322) suggesting separate equations for males and females (Table 2). The rate of change in weight relative to length was well marked upto the length of 482 mm. Thereafter there was no appreciable increase in weight with increase in length of the fish. Males were found to be heavier than females upto the length of 200-250 mm. Therefore, this size range (200-250 mm) represented the size of M. armatus at first maturity of female. A comparison of observed and calculated weight (Table 3) of M. armatus did not show a close agreement. Observed weight of juveniles and smaller individuals was less than their calculated weight, while in the individuals of larger size (more than 375 mm) it was more than the calculated weight (Fig. 2). Discussion LeCren's (1951) concept of cube law hypothetically suggests the value of 'b' for an ideal fish to be 3.0. This value has been used here as a scale for comparison. If the 54 value of 'b' is less than 3 then it indicates poor physical condition of the fish and if it is more than 3 it is indicative of its good physical condition. The value of 'b' exhibits both interspecific as well as intraspecific variations. Variation within the species is used to denote the environmental condition of the water body from which the fish has been captured. However, the value of 'b' may depart significantly from 3.0, so much so that it may lie between 2.5-4.0 (Hile, 1936; Martin, 1949). Antony Raja (1967) found the value of 'b' in the range of 2.0-5.4 in the case of marine teleosts. The departure from the cube law may be due to several factors. This can be explained in the light of ecological factors with special reference to availability of forage organisms to the fish. But genetic basis of the difference cannot be entirely ruled out. In addition, the change in morphology of the fish with advancing age may also be a reason for the departure noted here in the value of 'b' from its hypothetical value of 3.0. Mustafa (1978) observed variation in length-weight relationship associated with habitat differences in Esomus danricus, and emphasized that fishes living in running water show rapid growth compared to those which inhabit stagnant water. Since the specimens studied here were collected from river, lotic habitat, which results into an additive action of various factors such as circulation of water, high dissolved oxygen concentration, temperature and nutrients 55 etc., may be a reason for high (<3) value of 'b' derived for juveniles, males and females of M. armatus. Although, as noted above and as given in Table 2, the values of 'b' were different between males, females and juveniles, but marked maturity stage linked difference in value of 'b' failed to occur in different stages of males as well as females in M. armatus. The adult females of the size range 200-482 mm were found to be somewhat heavier than the males of an equivalent length. In addition to the possibility of their being in a better condition than the males, the development of ovaries in females might also be a reason for their higher weight in comparison to males. This, however, implies that at a given length of the adult stage females tend to be heavier than the males. The findings of Sarojini (1958) in the case of Mugil parsia, Chakraborty and Singh (1963) in the case of Cirrhina wrigala and Gowda et al. (1987) in the case of Valamugil seheli support the present findings regarding difference in 'b' values of males and females. However, Pillay (1957) did not find any significant difference in the value of 'b' between the two sexes of Mugil tade. Further, contrary to the present findings the work of Pathak (1975) on Laheo calbasu, Chatterji et al. (1977b) on Laheo hata, Hoda (1976, 1987) on Neir.ipterus japonicus and Boleopthalwus dussumieri, and Dawe (1988) in short finned squid, showed that in them the weight of males increased faster than the weight of females. 56 It is further observed that the length-weight curve plotted for males lies above the length-weight curve for females upto the length of 250 mm, and, thereafter, it lies beneath the length-weight curve for female (Fig. 2) . The same phenomenon was observed by Chakraborty and Singh (1963) in Cirrhina mrigala, and Khumar and Siddiqui (1991) in Puntius sarana. The point of intersection of the curves for males and females which occurred between 200-250 mm in the case of M. arTnatus, also represented the size of this fish at its first maturity (cfr.- alsen and Marriman (1946) in the case of Macrozoares americanus; Natraj an and Jhingran (19 63) in Cirrhina mrigala; Khan (1972) in the case of Labeo rohita, and Chatterji et al. (1977b) in the case of Labeo bata) . They have also emphasized that difference in the point of intersection of curves for the two sexes could be attributed to difference in growth between the males and females of their respective fishes. A comparison of the observed weight of M.armatus with its calculated weight showed that the observed weight of juveniles and adult individuals (up to the size of 374 mm in length) was less than their calculated weight (Table 3), but in large sized fishes (375-482 mm in length) it was more than the calculated weight. This shows that the growth in weight of this fish was more than the growth in its length in the large sized specimens. Similar observations have been reported by Jhingran (1952) and Khan (1972) in the case of 57 L. rohita, Chatterji et al. (1977b) in the case of L. bata, and Khumar and Siddiqui (1991) in the case of P. sarana. Contrary to this, however, Ansari (1988) reported a close agreement between observed and calculated weight in all length groups of Gadusia chapra. Summary The study of length-weight relationship of M.armatus revealed that the fish did not follow the cube law strictly and the weight increased was at a rate more than the cube of the length in both juveniles and adults. A significant difference was noticed in the value of 'b' among juveniles, males and females. The equations for length-weight relationship are W - 7.401 x 10 L3.3695 ^^^ juveniles, W = 1.415 X 10^ L^-°5^1^ for males, W = 7.8 x 10'^ L3.60328 ^^^ females and W = 4.4 x 10""^ L3. 29558 j^^, ^^le data of males and females combined. These length-weight relationship equations indicate that the females increased faster in weight than males. The significant variation of the value 'b' from expected cube law was tested by a 't' test. The values obtained for both males and females are highly significant at 5% level. The value obtained from covariance analysis for the difference between the slopes of regression lines obtained for males and females is 5.44 (d.f. 1,322), suggesting that separate equations are required for the two sexes. 58 Table - 1 Regression and parabolic equations o£ weight on length of M. armatus Source Regression equation Parabolic equation Correlation coefficiet'3 Juveniles Log W = -6.1307 + 3.3495 Log L 7.401 x 10 ^'^ ^3.3695 G.9763 Male Log w = -5.84910 + 3.09113 Log L 1.415 x 10'°^ L^-O^^^^ j- 97115' Female Log W = -7.10649 + 3.60328 Log L 7.800 x 10"°® j^3.60328 c.976362 Con-lDined (M&F) Log W = 6.35371 + 3.29558 Log L 4.400 x 10"°'^ ^3.2535= Q^ T. ir n a 2 < o sg 3 ^ S c c E: ft •^ «' 0 o B E. ?r 5- ft g B n ft "C w o o. p. 5- o *-f D t/i 00 ^ ft O 63 "1 1/3, o o ft o* -J o-J TS (A U) U) or cr o U) "p. o •o o •^ Is !-+> U) *o to LAI ft a. 00 U^—) 00 N) to 4^ ft LC o to OP y: p 1 ft f—t o O b b t/i o p. to 00 O X c o' ft o s n. ft ore N) o KJ »— ^— ft O^ 0^ O i-n 4^ ^ o t/3 o U) o NJ to ft ^ ft U) o ere' ** *— U) o Tl ft % ft 3- ' o ft B O 3 C TO ?r 3 vC ^ Calculated and observed weight of M. axmatus at different length intervals. Length Mean Observed Calculated groups value weight weight (mm) (g) (g) 72-124 138.05 12.007 12.0313 125-174 197.85 19.7368 18.3701 175-224 241.63 32.7083 31.3701 225-274 300.27 72.5333 64.7311 275-324 351.79 114.4385 109.0882 325-374 398.85 160.7195 164.9912 375-424 450.286 196.875 246.0802 425-482 481.00 267.400 305.85776 Ftg.1. Length - weight relationahips. A. Juvenle; B. Male; C. Female; D.Combind (M &F) JLogW M Loo W 2.3 F Log W CU>o W Fig. 2 Observed and calculated weight in different length groups of M. armatus Weight(g) 350 300 250 / 200 /^ 150 100 A- 50 .-.-ry^-^ 75-125 125-174 175-224226-274275-324325-374375-424425-48 Length groups (mm) Ob. wt. -^ Gal. wt. CHAnSR - VI Reproduction Introduction In the study of fishery biology it is essential to determine the maturation (stage of full growth and ripeness of gonads) and depletion of gonands. Because through such a study we can understand and perhaps predict the changes which the population as a whole is liable to undergo during the period of a year. Informations regarding the ecological and environmental conditions which are essential for breeding and the rate of regeneration of stocks can be inferred from these studies and are, in turn, helpful in determining the extent of recruitment in the population taking the population as exploitable stock. The knowledge of the total number of eggs produced by a fish during a year is of considerable value in knowing the spawning potential of fish stocks. This is so because in a biosphere the success and failure of a species largely depends on its spawning potential. The knowledge of the reproductive biology of a fish is also important in connection with its rational management. Data pertaining to reproductive potential of fish is used in formulating the degree of rearing facilities needed and to assess the success of operation of aquaculture. Investigations have been carried out on the 59 reproductive biology of both marine and freshwater fishes of India. Notable among those who worked on the reproductive biology of the Indian freshwater fishes are Jhingran (1961), Qasim and Qayyum (1961, 1963), Desai and Karamchandani (1968), Saxena (1979), Parmeswaran et al., (1970), Varghese (1980), Siddiqui et al. (1976a), Balasunder Reddy (1979), Kumari and Nair (1979), Devraj (1983), Mojumder (1987), Kader et al. (1988), Piska and Waghray (1989), Annigeri (1989), Lazarus (1990), Pillai (1990), Fatima and Khan (1993), Dobriyal and Singh (1993), Khan and Fatima (1994) and Madhusoodana Kurup and Kuriakosa (1994). A survey of the literature, however, despite their commercial importance very little work has so far been done on the biology of the spiny eels. Therefore, the present study was undertaken with a view to gather data on various aspects of breeding of Mastacembelus armatus with particular emphasis on sex ratio, gonad maturation, development of intraovarian oocytes, fecundity and spawning season of this fish. Materials and Methods 206 specimens of M. armatus collected from ponds and rivers in and around Aligarh district of western Uttar Pradesh formed the basis of the present observations. Length and Weight of the fish were recorded. For the purpose of calculating their sex ratio abdominal incision was made in 60 the body of eels for determinimg their sex because it was not possible to do so by morphological examination of the body. Stage of maturity was determined following the scheme suggested by Qayyum and Qasim (1964a) for the tropical and subtropical fishes. Identification of the stages of maturity of the gonads was done on the basis of their colour, general appearance and extent in the body cavity. Gonads were removed from the body and weighed on an electric balance sensitive up to 0.001 g. The gonadosomatic index (GSI) was calculated by expressing the gonad weight as a percentage of the intact- body weight of the fish. The extracted gonads were preserved in 5% formalin. Intraovarian eggs were taken out and their diameter was measured with the help of an ocular micrometer using 8 x 12.5 magnification of binocular dissecting microscope (Ernstleitz Gm bH wetzlar). For fecundity evaluation, 10 mg sub-samples of eggs were removed from the anterior, middle and posterior regions of each ovary . Ova present in each sub-sample were counted under 1 x 12.5 magnification of binocular dissection of microscope and their average count was multiplied by the total weight of the ovary for determining the absolute (total individual) fecundity. Relative fecundities (number of ova in unit body length, body weight, ovary length and ovary weight) were also computed. In addition, relationship of fecundity with various body dimensions like 61 body length, body weight,ovary length and ovary weight was also worked out. Results Sex ratio The sex ratio varied with the season. Monthly variations in abundance of male and female specimens of M. armatus have been indicated in Table 1 and Fig.l. The male: female ratio ranged from 1:0.5 to 1:1.2, with the average value being 1:08. In all months excepting February and September males maintained a marginal numerical superiority over the females. However, the chi-square test showed no significant departure from the hypothetical 1:1 ratio. The sex ratio also varied with size (Table 2 and Fig. 2) . Females were relatively less abundant in the higher size range (276-500 mm) , in which case the ratio ranged between 1:0.5-1:0.9, with an average value of 1:0.7. Gonads, sexual maturation and spawning The testes are paired, elongated and creamy white in colour. They are located dorsally in the abdominal cavity and, being placed in the middle of abdominal cavity, they elongate with ripening and extend towards the posterior half of the abdomen. They are suspended there by delicate and thin mesentries called mesorchia. From the anterior inner margin of each testis arises a vasefferens which runs along 62 the whole length of the testis. The two vasefferens of the two sides join posteriorly to form a common duct, the vasdeferens, which communicates with the exterior. The ovaries are also paired and elongated. They are situated in the posterior half of the body cavity and are suspended there medially by the mesovaria. Ripe ovaries are light yellow in colour. Anteriorly the two lobes representing the two ovaries are free, but posteriorly they bend downwards and inwards to form a short single oviduct which lead to the genital aperture. Five maturity stages are recognised in both males and females. Observations regarding general appearance of their gonads along with the colour of gonads and their extent in body cavity and gonadosomatic index (GSI) values are given below: MALE Stage I (immature virgin): Testes are narrow, thread like and translucent. Vasa diferentia not very distinct and difficult to locate. GSI 0.22 +_ 0.157. Stage II (maturing virgin and recovering spent: Testes slightly elongated, opaque and white in colour. Vasa deferentia distinct, easy to locate. GSI 0.43 +_ 0.029. Stage III (ripening): Testes more prominent than in stage II, creamy white in 63 colour. Viscous fluid oozes out if pressure is brought to bear on the abdomen. GSI 0.77 +_ 0.029. Stage IV (ripe): Testes creamy white in colour, grown to maximum size, occupying substantial part of the body cavity, and discharge white milt under gentle pressure. GSI 1.35 +_ 0.248. Stage V (spent): Testes shrunken, their weight drastically reduced. No milting. GSI 0.39 +_ 0.244. FEMALE Stage I (immature virgin): Ovaries small, thin, thread like semitransparent and creamy white in colour. Ova microscopic, semitransparent and devoid of yolk granules. Ova 0.073-0.18 mm in diameter. GSI 0.13 +_ 0.10. Stage II (maturing virgin and recovering spent): Ovaries slightly elongated and swollen, light yellow in colour and with ova small and visible to the naked eye. Ova 0.21-040 mm in diameter. GSI 0.81 +_ 0.057. Stage III (ripening): Ovaries more voluminous, light yellow in colour. Blood vessels seen ramifying over the surface of ovaries. Ova 64 with distinct yolk and visible to the naked eye. Ova 0.55- 1.01 mm in in diameter. GSI 1.44 +_ 0.147. Stage IV (ripe): Ovaries quite massive, occupying major portion of the body cavity. Ova easily ejected if slight pressure is brought to bear on the abdomen. Ova almost round, 1.16-2.05 mm in diameter. GSI 3.76 ± 0.49. Stage V (spent) : Ovaries flabby and shrunken, left with only a few residual undeveloped ova. Weight considerably reduced. GSI 1.31 + 0.063 . In both sexes the gonads showed a regular seasonal development with little overlap in different phases of maturation. The percentage of various maturity stages in different months is indicated in Table 3 and Figs. 3-4. The immature virgins (stage I) and maturing virgins or the recovering spent specimens (stage II) of both sexes were available in all months except June through August. It is evident from the present observations that in both sexes the gonads showed little activity during the period September through February. In March gonads developed rapidly and entered the ripening stage. This stage was predominant during April and May. In June both sexes were completely ripe. Ripe specimens were encountered upto August. Maximum number of spent individuals were recorded 65 during August and September. Gonadosomatic index (6SI) Remarkable changes in the weight of gonads were observed during development and maturity. Low gonadosomatic index indicated the inactive phase of the gonads. As gonadal activity picked up the GSI also increased, attaining its peak value in the ripe stage. In both sexes high values of gonadosomatic index were recorded during the period May through July indicating full development of their gonads (Table 4 and Fig. 5) . Compared to males, the seasonal changes in gonadosomatic index were more marked in females. In both sexes while the gonadosomatic index increased markedly from March, it declined abruptly at the onset of spawning in July as was indicated by the appearance of spent specimens among the specimens collected during that month. Occurrence of ripe individuals upto late August/early September shows the extent of the spawning period of M. armatus. Ova diameter The diameter of intraovarian oocytes was recorded in different months and their frequency distribution was also studied (Table 5 and Fig.6). Ova sampled from the anterior, middle and posterior regions of ripe ovary were almost of the same size. Likewise, the ova from the two lobes of gonads also had almost similar diameter. Fully developed 66 and ripe eggs (diameter 1.46-2.05 mm) were recorded during June. The condition of all the ova in an ovary being at the same stage of development is indicative of the fact that in place of fractional spawning, spawning in this fish takes place only once in a year. Fecundity Fecundity increased with size and weight of the fish. The number of ripe unspawned eggs varied between 927-7409 in specimens of M. armatus ranging between 12.0 - 48.2 cm in size. Length-wise the fecundity 'factor' varied between 53- 146, with an average of 63 eggs/cm and weight-wise it varied between 13-88 eggs/g with an average of 29 eggs/g of the body weight of the fish. The number of eggs (63) per cm of fish length exceeded the number of eggs (29) per g of fish body weight. The relationship of fecundity with both body length and body weight was worked out after logarithmic transformation of the data (Table 6 and Figs. 6-9) . In both cases significant correlation was noted (p<0.001), with the value of correlation coefficient for the relationship, body weight-fecundity being higher (r = 0.9151) than the value of this coefficient obtained for relationship body length- fecundity, in which case 'r' was 0.8595. At 0.99, the value of 'b' for fecundity-length relationship was close to 1, while the value of 'b' for fecundity-weight relationship it was 0.41. For further insight into the phenomenon of fecundity, 67 ovaries ranging between 4-98 cm in size and 0.8 - 41.8 g in weight were also studied. It was observed that the number of ova per cm of ovary-length varied between 253 - 756, with an average of 344 eggs/cm. Ova per g of ovary-weight varied between 177 -1108, with an average of 641 eggs/g. Results of the relationship of fecundity with both ovary length and ovary weight are presented in Table 6 and Figs. 8-9. Discussion Males usually out numbered the females in a population of M. armatus. This indicates the higher mortality suffered by female specimens particularly in the higher size range. This mortality can be related to the natural causes such as spawning stress or the pressure of selective fishing for larger sized fish. Hoda and Qureshi (1989) provided a similar report of proportionately more males than the females in Liza klunzingeri particularly in the lower length groups, and emphasized that this ratio might be affected by differential fishing factors related to seasons and schooling in feeding and spawning grounds. Gowda and Shanbhogue (1988) also observed the dominance of males over females in Valamugil seheli during all the months. However, it can be mentioned here that several other workers (Qayyum and Qasim, 1964; Rangaswamy, 1974; Effendi and Sjapei, 1976; Wijeyaratne and Costa, 1988; Annigeri, 1989) recorded the dominance of females over males. Presence of males and 68 females in equal number, ratio 1:1, was observed by Kumari and Nair (1979) in the case of Noemacheilus triangularis and by Chaudheri (1986) in Ompox birnaculatus. In M. armatus the cycle of maturation and depletion of gonads occurs only once in a year and is synchronised with the onset of monsoon rains because stage IV gonads (ripe) were recorded from late July to August, which obviously is its spawning season. The breeding behaviour in M. armatus follows a pattern which is common to all the freshwater fishes living in the plains of western Uttar Pradesh. Working on a number of freshwater teleosts found in the plains of Uttar Pradesh, Qasim and Qayyum (1961) found the period July through September to be their breeding season; and, emphasized that the breeding process has a direct relation with the monsoon cycle perhaps this is the reason why the breeding season in most fishes is not the same in different regions of this country. In western U.P and, further north, in Punjab the out break of monsoon is usually late and, therefore, the spawning is also delayed accordingly. Besides monsoon, other factors which affect the breeding process are high dissolved oxygen content, pH and temperature of water. Khanna (1958) pointed out that the chemical composition of water played no role in the spawning, and that the spawning in Indian major carps was mainly induced by the flood water having a current of moderate intensity. More recently, seduced breeding 69 behaviour was reported by Shah et al. (1990). Regarding the effect of temperature over spawning in fishes, several workers (Khan, 1924; Smith, 1945) have reported the optimum temperature conditions as a prerequisite for spawning, and the temperature range at which the major carps have been observed to breed seems to be between 75 to 86°F (Hora, 1945). In view of the fact that the spawning response of M. arwatus to the temperature, cloudy weather conditions and high dissolved oxygen was similar to that noted for other freshwater fishes of this region (studies cited above), no efforts were made here to correlate the physical factors with spawning in considering that the optimum physical conditions for its spawning are the same as have been noted for other fishes inhabiting the plains of north India. The observation regarding the spawning season was further supported by the gonadosomatic index (GSI) and the studies on size progression of ova during different months. The monthly variation of the GSI not only indicates the different phases of reproductive cycle but also gives a clue regarding the duration of spawning season. Increased GSI indicates the advancement of maturity. High gonadosomatic index in both sexes during the period May through July represents full development of gonads during these months. Recovering gonads (stage II) remained quiescent from October through January, because during this period both temperature and photoperiod remained minimum. But, as soon as the 70 temperature increased during February/March, an increase in the development of gonads also took place followed thereafter by rapid changes in gonads. The peak condition of the development of gonads was recorded during June when both temperature as well as photoperiod were maximum. Most of the Indian freshwater fishes have been reported to have a relatively brief spawning season. They spawn after the onset of monsoon which in northern parts of the country occurs during late June/early July. Occurrence of a high percentage of mature individuals and an increase in the number of spent fish in June/July revealed the beginning of the spawning period which in M. armatus continues till early September. On the basis of the ova diameter frequencies, Qasim and Qayyum (1961) classified various species of fish into three categories: Category I All those species which have a single batch of maturing eggs in their ovaries. Spawning in them takes place only once in a year during a definite short period. Category II All those species which have more than one batch of maturing oocytes. In them repeated spawning takes place during the monsoon season. 71 Category III All those species which have oocytes of all sizes ranging from the smaller immature oocytes to the large and mature ones present with or without demarcation into batches. In them spawning takes place throughout the year. The presence of ova of same diameter in ripe ovary of M. armatus showed that there was a single well marked group of oocytes present in it. This unimodal occurrence of mature eggs in the ripe specimens of M. arwatus is indicative of only one spawning period in this fish (category I) . Similar observations were made by Qasim and Qayyum (1961) in another spiny eel, Rhyncobdella aculeata. As regards the relative fecundity, the number of eggs per unit length exceeded the number of eggs per unit body weight in M. armatus. Similar results were obtained by Piska and Waghray (1989) in Salmostoma bacaila, Pathani (1981) in Tor putitora and Bisht and Upadhaya (1979) in Barilius bendelisis. When weight of M. armatus was taken into consideration, the fecundity of this fish was found to be exceedingly low. For instance, a specimen of the mullet, L. klunzingeri, weighing 23-40 g was reported to contain as many as 40,500 eggs in its ovaries (Hoda and Qureshi, 1989). But when a comparison was made between the weight of the present fish and the number of eggs produced by it, the fecundity in its case was found to be 32 times lower than that observed in the case of L. klunzingeri. Karim and 72 Hossain (1972) reported the occurrence of low absolute fecundity (2013 eggs on an average) in a closely related species, Mastacemhelus pancalus. Results of the present study indicate that fecundity is significantly correlated with both length and weight of the ovary as well as the length and weight of the fish. A linear relationship was found to exist between fecundity and each one of these four characters. The value of 'b' for fecundity-body length relationship was found to be close to unity. A very wide range of the values of 'b' for fecundity-body length has however, been reported for Indian fishes. Saigal (1964) and Devraj (1973) found that fecundity varied 1.04 and 1.6 times the both length in Mystus aor and Ophiocephalus marulius, respectively. Piska and Waghray (1989) and Hoda and Qureshi (1989) observed value of 'b' to be 3 in both S. bacaila and L. klunzingeri, Varghese (1980) found this value to be 5 in the case of Coila dessumeri. The value of 'b' for fecundity-body weight was much lower than that for the fecundity-body length relationship, suggesting that the rate of egg production in relation to increase in weight of this fish was lower than the rate of egg production in relation to increase in its length. A number of workers (Bhatt et al. , 1977; Piska and Waghray, 1989 and Hada and Qureshi, 1989) have reported the occurrence of a similar linear relationship between these two parameters. Comparison of the quantitative variation in fecundity with both length as well 73 as weight of the ovary revealed a marked increase in egg production with increase in ovary length. Summary Breeding process of the fish was examined. Population of M.armatus was slightly dominated by males. The male: female ratio ranged from 1:0.50 to l: 1.2 with the average ratio being 1:0.8. Sex ratio varied with different size range of this fish and with change in season. Gonads were differentiated into five phases of maturation with stages, I, II, III, IV and V representing immature virgin, maturing virgin and recovering spent, ripening, ripe and spent specimens respectively. Seasonal activities of the gonads were clearly demonstrated. The gonado-somatic index was related to the stages of development; it increased with the development of gonad. In both the sexes high values of gonado-somatic index was recorded during the period May through July. Change in the index were more marked in females. Spawning in M. armatus commenced in late June/early July. Spawning coincides with onset of monsoon. Occurrence of ripe individuals upto late August/early September shows the extent of the spawning of this fish. The fish spawns only once in a year. There was no evidence of fractional spawning as oocytes in each individuals were all of same diameter showing only one batch. Fecundity increased with growth in length and weight of fish of the 74 size 12-48.2 cm produced 927-7409 eggs. The fecundity 'factor' was 63 egg cm"-^ boby length and 29 eggs g" body weight respectively. Fecundity-body length progression was stronger than fecundity-body weight relation. These relationships have been quantitatively evaluated. 75 Table - 1 Sex ratio of M. armafcus in different months Months No.of No.of %age of %age of Combined Ratio X Signi- males females males females number (M:F) ficance January- 15 08 65.2 43 .8 23 1:0.53 2.130 NS February 14 15 48.3 51 .7 29 1:1.07 0.034 NS March 16 14 53.3 46 .7 30 1:0.87 0.130 NS April 18 16 52.9 47 .1 34 1:0.88 0.117 NS May 14 12 53.8 46 .2 26 1:0.86 0.153 NS June 20 10 66.7 33 .3 30 1:0.50 3.330 NS July 12 80 60.0 40 .0 20 1:0.70 0.800 NS August 20 21 48.8 51., 2 41 1:1.05 0.024 NS September 16 20 44 .4 55., 6 36 1:1.25 0.444 NS October 20 15 57.1 42., 9 35 1:0.75 1.714 NS November 14 08 63.6 36., 4 22 1:0.57 1.636 NS December 10 05 66.7 33. 3 15 1:0.50 1.666 NS Total 189 152 341 Mean 15.75 12.6 56.73 43.27 38.41 1:0.79 NS = Non Significant Table - 2 Sex ratio of Af. armatus in different size groups Size No.of No.of %age of %age of Combined Ratio Chi- Signi- (mm) males females males females number (M:F) square ficance 50-75 08 07 53.3 46.7 15 1:0.87 0.066 NS 76-100 10 12 45.5 54.5 22 1:1.20 0.181 NS 101-125 16 13 55.2 44.8 29 1:0.81 0.310 NS 126-150 12 14 46.15 53.8 26 1:1.16 0.153 NS 151-175 06 03 66.7 33.3 09 1:0.50 1.000 NS 176-200 09 11 45.0 55.0 20 1:1.22 0.200 NS 201-225 05 02 71.4 28.6 07 1:0.40 1.285 NS 226-250 00 02 00.0 10.0 02 0:2.00 2 .000 NS 251-275 00 00 00.0 00.0 00 0:0.00 0.000 - 276-300 20 18 52 .6 47.4 38 1:0.90 0.105 NS 301-325 17 12 58.6 41.4 29 1:0.70 0.862 NS 326-350 20 12 62 .5 37.5 32 1:0.60 2.000 NS 351-375 14 10 58.3 41.7 24 1:0.71 0.666 NS 376-400 10 07 58.8 41.2 17 1:0.70 0.529 NS 401-425 09 05 64 .3 35.7 14 1:0.55 1.142 NS 426-450 15 12 55.5 44.5 27 1:0.80 0.333 NS 451-475 10 06 62.5 37.5 16 1:0.60 1.000 NS 476-500 08 06 57.2 42 .8 14 1:0.75 0.285 NS Total 189 152 341 NS ::: Non Significat Table - 3 Occurrence of the spiny eel belonging to different maturity stages in different months Months Stage - I Stage - II Stage - III Stage - IV Stage - V no. % age no. % age no. % age no. % age no. % age Male January- 7 46.7 8 53.4 ------February 8 57.1 6 42.9 ------March 6 37.5 8 50.5 2 12.5 - - - - April 5 27.8 9 50.0 4 22.2 - - - - May 2 14.3 5 35.7 5 35.7 2 14.3 - - June - - - - 5 25.0 15 75.0 - - July - - - - 6 24.0 19 76.0 - - August ------5 25.0 15 75.0 September 6 37.6 5 31.2 - - - - 5 31.2 October 8 40.0 12 60.0 ------November 8 57.2 6 42 .8 ------December 4 40.0 6 60.0 ------ Female January 3 37.5 5 62.5 - - _ _ _ „ February 4 26.7 11 73.3 ------March 2 14.3 9 64.3 3 21.4 - - - - April 3 18.8 4 25.0 8 50.0 1 6.2 - - May 2 16.7 3 25.0 6 50.0 1 8.3 - - June - - - - 1 10.0 9 90.0 - - July - - - - 2 11.1 14 77 .8 2 11.1 August - - - - 2 9.5 11 52.4 8 38.1 September 4 20.0 2 10.0 - - - - 14 70.0 October 11 73.3 4 26.7 - - _ _ _ _ November 3 37.5 5 62.5 - - _ _ _ __ December 2 40.0 3 60.0 ------Table - 4 Gonado soma tic index of males and females of M. armatus in different months Months Gonadosomatic Gonadosomatic index (males) index (females; January- 0.42 + 0.018 0.79 + 0.045 February 0.45 ± 0.040 0.88 + 0.086 March 0.55 ± 0.019 1.03 + 0.052 April 1.00 + 0.039 1.85 + 0.243 May 1.26 ± 0.081 3.17 + 0.493 June 1.58 ± 0.211 4.52 + 0.793 July 1.22 + 0.153 3 .61 + 0 . 184 August 0.67 + 0.061 1.68 + 0.083 September 0.51 ± 0.065 1.09 + 0.054 October 0.41 + 0.022 1.16 + 0.083 November 0.22 + 0.013 0.13 + 0.100 December 0.22 + 3.130 0.77 + 0.040 Table - 5 Size-frequency distribution of intraovarian oocytes of M. armatus Size March April May June no.of %age no.of %age no.of %age no.of ova ova ova ova 0.40-0.55 05 8.0 - _ _ _ - 0.56-0.70 06 9.5 - _ . _ _ 0.71-0.85 12 19.0 08 12.9 0.86-1.00 26 41.3 11 17.7 05 7.1 1.01-1.15 10 15.9 25 40.3 14 20.0 - 1.16-1.30 04 6.3 15 24.2 28 40.0 - 1.31-1.45 - - 03 4.8 17 24.3 - 1.46-1.60 - - - - 06 8.6 07 1.61-1.75 ------25 1.76-1.90 ------25 1.91-2.05 ------10 TABLE - 6 Regression analysis o£ fecundity relations in M. armatus Parameters Regression equation Correlation Signi- co-efficient ficance Logarithmic Parabolic Body length Vs Fecundity Log F=1.83 + 0.99 Log L F=6.7xl0-^ L*^-^^ 0.8595 P O.OC: 'L' "F' Body weight Vs Fecundity Log F = 2.50 + 0.41 Log W F=3.1x±C^ h^ •^'^ 0.9151 1 f.CO: " BV;' - F' Ovary length Vs Fecundity Log F = 1.74 + 1.88 Log OL F = 5.4xl0''" L"^"^^ 0.932" ? u.o:: 'OL' -F' Ovary weight Vs Fecundity Log F=3.21 + 0.14 Log OW F=1.6xl0-^ OVi^--*-^ 0.6715 i l.i:i > 01-;' - p' Fig. 1 Seasonal vahatlons of sex ratio in M. arm at us Percentage JAN. FEB.MAR.APR.MAY. JUN. JUL.AUG.SEP.OCT.NOV.DEC. Months % of males % of females N' II I I I I I -;*•,, I O ^ o-^airoO">joitoO">joir>jO-Nioiroo^ -j^ ooiooioaiooiocjiooioaioaioai 0) X o o IV3 O Oi (Q 3 (Q 2 • CO "0 o 0) l>0 O c (D ^ •D c: 3 O •-* CO Co 0) (Q (0 (-Dn 3 D) (0 a> CD 05 o CD 00 o Fig. 3 Seasonal variations of maturity stages in M.armatus Percentage 20 15 10 0 i I i. JAN. FEB.MAR.APR.MAY. JUN. JUL. AUG.SEP.OCT.NOV.DEC. Months KwwM Stage I Stage 11 Stage III Stage IV Stage V (Males) Fig. 4 Seasonal variations in gonado somatic index (GSI) of Marmastus GSI Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Months GSI(Maies) GSI(Femaies) Fig. 5 Size-frequency distribution of intra ovarian oocytes of M.armatus Percentage of the no of ova 0.40-0.56 0.71-0.86 1.01-1.16 1.31-1.46 1.61-1.76 1.91-2.0 Size of the Ova(mm) March April -*- May June Fig. 6 Relationship between fecundity and body length of M.armatus Log F 3.9 3.7 3.5 3.3 3.1 Log F-1.83+0.99 Log L y 2.9 r f- 2.7 J L 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Log L Fig. 7 Relationship between fecundity and body weight of M.armatus Log F 3.9 3.7 3.5 3.3 Log F-2.50+0.41 Log W 3.1 J L J I L 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Log W Fig. 8 Relationship between fecundity and ovary length of M.armatus Log F 3.5 Log F • 1.74*1.88 Log OL 2.5 X ir^ 0.3 0.4 0.6 0.6 0.7 0.8 0.9 1 Log OL Fig. 9 Relationship between fecundity and ovary weight of M.armatus Log F 3.5 3.45 3.4 Log F • 3.21*0.14 Log OW 3.35 f^ 3.3 1.0 1.1 1.2 1.3 1.4 1.6 1.6 1.7 Log OW CHAPTER - Vn Culture Introduction The spiny eel, M.armatus, is in high demand in several parts of the country because of its palatibility and nutritive value however, as already indicated earlier in this thesis, the catch sold in the market comes from the wild sources like swamps, beel, etc. Despite its conomic importance no attempt seems to have been made so far to culture this species in ponds because of the lack of knowledge of its biology, growth, survival and the availability of its seed etc. Spiny eels are found in a variety of habitats. They usually burrow in the drying ponds during the day time and can even remain buried there for some months during summer. The spiny eel is an air- breather and can survive in mud and oxygen-deficient water for a long time (Datta Munshi and Hughes, 1992) . It is unfortunate that a versatile biological material like the spiny eel, which is suitable for fish production in adverse environmental conditions like swamps and derelict ponds, has not acquired the same position as is given to other Indian air-breathing fishes like Ophiocephalus, Clarias, Heteropneustes, Anahas etc., which have been able to attract more attention of the scientists also. In India, about 0.6 million hectare of water area is reported to be swampy and 76 unsuitable for the production of Indian major carps due to weed infestation and derelict ecology. Therefore, M. arwatus by virtue of its being hardy in nature adaptative to adverse environmental conditions, and having the capacity to breath air can serve as an excellent material for the utilization of these swampy and weed-infested water bodies. Even it can be cultured in sewage fed-waters. Rational management of its juvenile stage (fry) is essential to meet the demand of stocking material for aquaculture. In view of this, experiments were conducted on the culture of fry of M. armatus in a nursery pond and a cemented cistern, using artificial feed. For this purpose the fish were collected at Aaram Bagh, West Bengal and were brought to Aligarh. Materials and Methods A total of 400 juveniles of M.arwatus 60 to 70 mm in length (average 64 mm) were stocked. The rate of stocking was 15,000/ha. Before their release in the pond they were kept in a cemented cistern (2.4 x 0.85 x 0.7 m) for acclimatization. The cistern was filled with water from an earthen (unplastered) pond. Fishes were held in the cistern for a week. The nursery pond which was used for stockng is located in Aligarh (Lat.27° 34' 30" N. long;78° 4' 26" E),and its layout is shown in Fig. l,|^lates 1-2. Total area of the pond is 0.0263 ha (263 m'^^) and its average depth is 1 m. There is an island like structure in the centre of this pond and a bridge on either side of it connects this structure with the two sides of the pond. The pond is well exposed to the air and sunlight. During the monsoon this pond neither receives any sewage water nor any surface run off. It is equipped with an inlet pipe connected to a tube- well. Its dewatering is done by a motor operated pump. Before starting the culture of M.armatus the pond was dewatered and left in this condition for fifteen days in order to eradicate the predatory animals. Afterwards, the tube well water was pumped in it up to a desired level. No liming and manuring was done. A feed consisting of chopped offals and rice bran was given at the rate of 5% body weight once a day. Fish were sampled on a monthly basis for conducting various observations. Total length was measured from the tip of snout to the longest caudal fin ray. Weight was recorded on an electric balance Stanton (England) model F5P. Water temperature was recorded using a mercury thermometer graduated upto 100°C. Dissolved oxygen was estimated by Winkler's modified technique (APHA, 1980). Free carbon dioxide of the pond water was estimated by taking 100 ml sample in a conical flask and titrating it with 0.05 N NaoH, using phenolphthalein as an indicator. Total solids were determined by weighing the residue left after evaporation of 78 an unfiltered sample of 500 ml. For total dissolved solids the same method was applied using a filtered sample. Total suspended matter was estimated as the difference between the readings for total solids and total dissolved solids. In the cemented cistern 80 juveniles of M. armatus (total length 75-85 mm and body weight 1.35-2.73g) were released. A feed consisting of chopped offals and rice bran was given at the rate of 5% body weight once daily. Feeding in both nursery pond and cemented cistern continued for specified period of cultivation, after which fish were taken out and measured for their length and weight. Specific growth rate of fish both from nursery pond and cemented cistern was calculated by using the equation: Log e W2 - Log e W-, SGR (%) = X 100 D where, SGR = Specific growth rate W2 == Final weight of biomass (g) W-j^ := Initial weight of biomass (g) D = Duration of feeding Relative growth rate was calculated by the following formula: W^ - W^ RGR (%) = X 100 where, RGR = Relative growth rate 79 W^ = Final body weight (g) W-"- = Initial body weight (g) Harvesting Drag and cast nets were used for capturing the individuals of M. armatus stocked in the nursery pond. But, it was found that even after repeated netting in this small pond not more than 25% of the total stock could be collected. Therefore, dewatering of the pond and collection of the fish with the help of a hand net was resorted to for the effective harvesting of M. armatus. Growth and production After a period of 100 days the nursery pond was drained and 238 individuals of M. armatus in the length range of 105 to 142 TTim (average length of 127 mm) were recovered. Table 2 presents details of experiments, growth rate and survival etc. of those specimens of M. armatus which were kept in nursery pond as well as those which were in cemented cistern. In the nursery pond the body weight ranged between 9.39 to 13.13g (average weight 10.20 g) . Thus during those 100 days during which the specimens were in nursery pond the gain in their body length was 62 mm while gain in their body weight was 9.44 g. The rates of increment of body length and body weight were computed as 0.62 mm/day (18.6 mm / month) and 0.0945 g/day (2.835 g/month) respectively. The relative growth rate (total percentage of weight gain) and 80 specific growth rate of M. armatus during 100 days in nursery pond were 716.1% and 2.107% respectively. In the pond area of 263 m^ the total yield was found to be 2.5 kg (estimated as 93.1 kg/100 days) during the above mentioned rearing period. The survival rate was about 60% . In the cemented cistern the average value for gain in body weight was 3.09 g in 30 days with the rate of body weight increment being 0.1030 g / day (3.09 g / month). This value was greater than the value obtained for body weight increment observed in those specimens which were in the nursery pond. The juveniles which were stocked in the cemented cistern were larger in size as compared to the juveniles of nursery ponds and this was the reason for the high value of body weight increment in the specimens of cemented cistern as compared to that of nursery pond (Table 2) . The specific and relative growth rates for increase in body weight of fish kept in the cemented cistern were 3.217% and 161.78% respectively. At the time of harvesting the average length and weight of fish in the cemented cistern were 90 mm and 5g respectively. Their survival rate was 65%. Hydrology of pond & cistern water During the period of stay of the spiny eels in the nursery pond the physico-chemical conditions of water there were as follows : The water temperature ranged between 32°C and 38°C. The dissolved-oxygen content of the water ranged between 7-11.4 mg/L. Free carbon dioxide was almost nill through out the cultivation period. A mixture of bicarbonate and carbonate alkalinity contributing to total alkalinity varied between 200 to 340 mg/L. Maximum load of suspended solids (26300 mg/L) was recorded in the month of November. Total dissolved solids fluctuated marginally during the cultivation period with the maximum and minimum values being 38,000 mg/L and 35000 mg/L. Thus, fluctuations in total solids were due to the variations in suspended substances. During the cultivation period the surface temperature recorded in the cemented cistern ranged between 27.0-29.0°C. In this case the dissolved-oxygen ranged between 6-9 mg/L and free carbon dioxide was also nil in this pond through out the culture period of 30 days. Economics Details of the computation of the variable cost and return functions of the cultivation system of M. armatus, worked out for a 1 acre (0.4 ha) pond (which is usually the size of a village pond), are given in Table l. The net return on variable cost was worked out to be 128.67%. The cost of fish production was around Rs 15.30/Kg. Therefore, it can be said that an investment of Rs. 8,265.00/- can in six months time assure a return of Rs 18,900.00/- in the western Utter Pradash. 82 Discussion The growth and survival of a fish mainly depends on the trophic and hydrological conditions of the water which it inhabits. Therefore, the growth pattern varies in different water bodies. In the present experiments, the juveniles of M. armatus kept in two different environments showed two different growth rates even when they were given similar artificial feed. The fish in nursery pond showed a relatively slow growth of 2.83g/ month as compared to the fish kept in the cemented tank where this value was found to be 3.09 g/month. Moreover, the juveniles of M. armatus caught from the natural environment such as ponds and rivers, and which were similar in length to those individuals which were collected from the nursery pond and the cemented tank, were found to be heavier than the latter. This is indicative of comparatively latter growth in the individuals of M. armatus collected from natural habitat. As already mentioned in the chapter on food and feeding in M. armatus in the text of this thesis, the younger individuals of this fish are highly carnivorous and chiefly feed on earthworms and insect larvae. Adult fish is highly predatory and feeds on prawns and fish present in its natural habitat. The nursery pond which was used for the present experiment is a newly constructed structure and, therefore, it was not rich in the invertebrate fauna which is, by and large, the main food of the juveniles. 83 Therefore, this may be the reason for the relatively slow growth of juveniles of M. armatus in the nursery pond. Biologically productive natural waters with rich macro- invertebrate fauna would be ideally suited for the growth of the young of this fish, and the ponds rich in crustaceans and forage fish would be ideal for the adults. Moreover, the living organisms taken as food by M. armatus are superior to the artificial food such as meat and fish meal powder, because in addition to providing food they cater to its food catching habit also. Devraj (1973) working on the culture of fry and fingerlings of air-breathing carnivorous murrel, Ophicephalus marulius, also reported similar results showing a high growth rate in the individuals of this fish collected from natural environment rich in invertebrate fauna than those reared for 3 months on artificial feed in the nursery pond. Being an air-breather, the spiny eel permits high rate of stocking. In the present experiment, the survival rate was found to be 60% on the stocking rate of 15,000/'ha. But, this fish may be stocked for monoculture at the rate of 15,000 to 25,000/ha like other air-breating fishes. It is, however, necessary to do further experiments with this bottom feeding predatory fish before it can be recommended for polyculture with fishes like large sized Indian major carps {Catla, Labeo) and exotic carps. 84 As noticed during the course of this study, M. arrnatus could be effectively caught only with a hand net after dewatering the pond completely. This is so because they are able to avoid the collecting gears by burying themselves into the muddy bottom of the pond. Therefore, M. armatus poses severe technological problem in harvesting. While discouraging the need for evolving effective traps and devices for capturing it. Cage culture may, however, be a suitable solution for getting better retrieval of the stock of M. armatus with negligible effort invoved in catching it. The cages can also be conveniently utilised for culturing this fish in unmanageable weed infested ponds. Although, a cheap and durable cage material is yet to be found out, the split bamboo or synthetic fibre can be used in fabricating these cages. Cages made of synthetic fibre are already being used for culturing air-breathing murrels and catfishes in many parts of the country. Therefore, this type of cage can also be utilised for successfully culturing the spiny eel, M.armatus. Sximmary The two experiments done in connection with the culture of fry of M. armatus were conducted in nursery pond and cemented cistern, using artificil feeding. The stocking rate of fry was 15,000/ha in both the cases. In nursery pond the experiment was carried out for 100 days. It was 85 run for 3 0 days in the cemented cistern. The rate of body- weight increment was 2.835 g/month in the nursery pond and 3.09 g/month in the case of cemented cistern. The specific and relative growth rates were 2.107% and 716.1 % respectively in the case of fish kept in nursery pond and 3.21% and 161.75% respectively in the case of fish kept in the cemented cistern. In the nursery pond with an area of 263 m^ the total yield was found to be 2.5 kg (estimated as 93.1 kg/ha/100 days) in 100 days of cultivation on 60% survival. 86 Table 1 Variable cost and return functions of Af. armatus culture for six months under semi-intensive culture management. (A) Expenditures S.No. Items Quantity Rate(Rs.) Total amounts 1. Rent of Water body- 1,000/ha 400.00 2. Pond preparation with 1,000 Kg 100/100 Kg 1,000.00 tnahua oil cake 3. Fingerlings 6,000 nos 25/lOOnos. 1,500.00 4. Feed cost 105 Kg 03/ Kg 315.00 5. Medicine cost 50.00 6. Netting charges 300.00 7. Labour charges 1,200.00 8. Interest on working 15%annum 1,500.00 capital 9. Incidentals/contingencies 2,000.00 Total variable cost = 8,265.00 Stock ing, survival and production: (B) . Stocking rate Survival Growth Net Producti (per 0.4 ha) rate % (g) (Kg) 6,000 60 150 540 (C) . Return: Quantity of fish for sale Ratel @ Total amounts (Kg) (Rs/Kg) Rs P 540 35 18, 900 00 (D). Net Profit: C - A = Rs. 18,900.00 - 8,265.00 Rs 10,635.00 Percentage of return on variable cost 128.67% Cost of production per Kg of fish 15.30 2. O o 3 '^ « 3 ^ IS 3 o I E •^ uj _o §5 2. 5" o o till 1 9 a ^ o o o 2 Si o o o o 5- 9, 05 30 ON --•N '— Vw 1^ •u 2 =3 < 3 5' en vO k) @.^^ "•• m 00 X O o 11 3' o o 6? s: 3 o o 3 5 en en >o .^ "n o -J s ^ <3 3- 9 o ® ^ ^ ein 3 o Si &3 2 -*> 00 era rs en e H K) tJ ;^ <3* "^ 05, S' —' 2; o O n" O 3 E. en a\ OS K> to ON (B Q S —' ^ 0\ O ^ ** 1 M •o •"* K) 00 •(>. o\ /—s o (fi* "^ Ul ^1 CA 2. ™ 0. Fig. 1. Layout plan of nursery pond. TO 010 r CHUNGI-*- -»• TO ENGG.COLLEGE Plate 1-2. Nursery pond of M. armatus Summary Summary The work done on the biology of Indian freshwater fishes mainly deals with the carps, murrels and the cat fishes. But no attention has been paid to the study of the biology of the spiny eel, Mastacembelus armatus (family: MastaceTTLbelidae) , which is palatable and nutritive. The spiny eels sold in the market are brought almost entirely from their natural population. In view of their dwindling natural population, the situation demands that scientific methods be applied for culturing these eels. But, development of a suitable method for their aquaculture is inconceivable without a sound knowledge of their biology. Keeping in mind the poucity of information on the biology of Mastacemhelus spp. in general, an attempt was made here to study the biology of M. armatus, which is the most important of the four species of the genus Mastacembelus found in India. The spiny eels occur in tropical Africa and Asia onl}'. In all there are thirty- three species of freshwater spiny eels which have been housed in four genera, two of which namely, Macrognathus and Mastacembelus are under sub-family Afromastacembelinae. Species of the genus Mastacembelus found in Indian region are M. armatus, M. oatesii, M. 87 alboguttatus and M. dayi. Out of these, the species M. alboguttatus and M. dayi are rare in occurrence. As far the remaining two species, while M. oatesii attains a length of about 3.7 cm, and being of a small size is of no interest to fisheries, M. armatus attains a length up to 65 cm and is considered the largest spiny eel found in India. M. armatus is, therefore, of interest to fisheries, the more so because it is considered to be very good table fish particularly in the plains of India where it is very popular especially when sold in live condition. The spiny eel, M. armatus, is restricted to Asia. It has been reported from Pakistan, Sri Lanka, Bangladesh, Myenmar through Thailand, Malaysia and southern China. It occurs in a variety of freshwater habitats in the plains as well as in the hills of India. It is common in rivers, lakes, ponds, streams and estuaries. The fish patrols a body of water throughout its length and breadth but spends major part of its life at the bottom of the water. The samples were collected from Kalinadi, a tributary of the river Ganga at Aligarh for stock analysis study. Various morphometric and meristic characters alongwith the study of length -weight relationship were used for stock discrimination. Riverine population of M. armatus was found to consist of two stocks which have been denoted here as stocks A and B. These stocks were sympatric and differed in a number of morphometric and meristic characters. The 88 regression of different body measurements like standard length, head length, snout length, caudal fin length, predorsal length, body depth, body width, caudal fin depth, interorbital width and optic diameter on totat length was studies, as a result of which a linear relationship was noted to occur between them in the fishes of both the stocks. Correlation of coefficient in all the above mentioned relationship was highly significant. Various body proportions are expressed here as percentage of total length. Significant difference in the sets of characters head length/total length, standard length/total length, pre dorsal length/total length, body depth/total length, body width/total length have been found between the fishes of stocks A and B. The equations obtained for length-weight relationships in the fishes of these two stocks were also different. Appreciable difference in growth of weight relative to length was noticeable in these two stocks. Stock A which demonstrated faster growth (weight per unit length WPUL = 3.75g) occurred with 37.12% frequency, whereas stock B (WPUL =1.85 g) was more preponderant (62.88%). The spiny eel, M. armatus is highly predacious in nature and prefers live aquatic crustaceans and insects as their food. Well developed dentition, strongly built stomach and short intestine are some of the characteristics which were related to the fish's dietary composition. M. armatus has an uneven gill arch surface in place of gill rakers. There was no 89 major shift from a basically carnivorous orientation in the feeding activity of this fish during its various stages of growth. Gut contents analysis showed that macrocrustaceans (especially shrimps) and forage fish were the main food of the adults while annelids and aquatic insects were taken by the young specimens. Molluscs and aquatic vegetations were consumed as incidental items. Gut length/ body length ratio of the fish varied from 1:0.50 to 1:0.68, foraging activity fluctuated with season. Feeding intensity was high in early maturity stages and was got relatively lower in fish with ripe gonads. Adult specimens consumed more food in summer than winter and rainy season. Food intake in younger specimens was greater in post-monsoon period and autumn, but pronounced feeding activity was observed in the month of October. Extremely low feeding was observed in the month of December. In adults maximum number of empty guts were found during spawning and in winter. The study of length-weight relationship of M.armatus revealed that the fish did not follow the cube law strictly and the weight increased was at a rate more than the cube of the length in both juveniles and adults. A significant difference was noticed in the value of 'b' among juveniles, males and females. The equations for length-weight relationship are W = 7.401 x 10°"^ L3.3695 ^^^ juveniles, W = 1.415 x 10°^ L^-°51^3 for males, W = 7.8 x 10"°^ L3.60328 fQ^ females and W = 4.4 x lO'^"^ L^-29558 ^^^ ^^^ 90 data of males and females combined. These length-weight relationship equations indicate that the females increased faster in weight than males. The significant variation of the value 'b' from expected cube law was tested by a 't' test. The values obtained for both males and females are highly significant at 5% level. The value obtained from covariance analysis for the difference between the slopes of regression lines obtained for males and females is 5.44 (d.f. 1,322), suggesting that separate equations are required for the two sexes. Breeding process of the fish was examined. Population of M.armatus was slightly dominated by males. The male : female ratio ranged from 1:0.50 to 1: 1.2 with the average ratio being 1:0.8. Sex ratio varied with different size range of this fish and with change in season. Gonads were differentiated into five phases of maturation with stages, I, II, III, IV and V representing immature virgin, maturing virgin and recovering spent, ripening, ripe and spent specimens respectively. Seasonal activities of the gonads were clearly demonstrated. The gonado-somatic index was related to the stages of development; it increased with the development of gonad. In both the sexes high values of gonado-somatic index was recorded during the period May through July. Change in the index was more marked in females. Spawning in M. armatus commenced in late June/early July. Spawning coincides with onset of monsoon. 91 Occurrence of ripe individuals upto late August/early September shows the extent of the spawning of this fish. The fish spawns only once in a year. There was no evidence of fractional spawning as oocytes in each individuals were all of same diameter showing only one batch. Fecundity increased with growth in length and weight of fish of the size 12-48.2 cm produced 927-7409 eggs. The fecundity * factor' was 63 egg cm"-*" body length and 29 eggs g" body weight respectively. Fecundity-body length progression was stronger than fecundity-body weight relation. These relationships have been quantitatively evaluated. The two experiments done in connection with the culture of fry of M. armatus were conducted in nursery pond and cemented cistern, using artificial feeding. The stocking rate of fry was 15,000/ha in both the cases. In nursery pond the experiment was carried out for 100 days. It was run for 3 0 days in the cemented cistern. The rate of body weight increment was 2.835 g/month in the nursery pond and 3.09 g/month in the case of cemented cistern. The specific and relative growth rates were 2.107% and 716.1 % respectively in the case of fish kept in nursery pond and 3.21% and 161.75% respectively in the case of fish kept in the cemented cistern. 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