GENERAL SUMMARY. Observations

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Emory Bridges
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1 GENERAL SUMMARY Observations The seasonal variation in the gonadosomatic indices (GSI) of male and female confirmed that the spawning season of Lepidocephalus thermalis was from October to November, coinciding with the highest rainfall, lowest temperature and shortest daylength of the year. This is considered as the major spawning season of L.thermalis during the North-East monsoon months in India. The mean GSI of female L.thermalis was 7.285% in early October, % in late October and % in the first fortnight of November. After mid-november, the GSI was as low as 5.942% indicating that spawning in L.thermalis had already occurred. This denotes that fully ripe females were found only in the first half of November and spawning occurred in the middle of that month. The spawning was synchronic, total and occurred in a restricted period. The highest range of GSI of female L.thermalis was between % for a fish of 37 mm standard length and 534 mg weight, and % for a fish of 39 mm standard length and 735 mg weight in early November. Moreover, during the South-West monsoon from the end of April to early June, the impact of monsoon rain was realized in the fish that there was a small peak in GSI of both male and female, indicating a minor breeding season. Only 30% of the females were found to be gravid. Thus Lepidocephalus thermalis is considered to be a biannual monsoon breeder. Seasonal changes in condition factor (K) were similar between males and females. It increased starting from October through December, and then decreased up to March. Again there was a slight surge in April up to June, and thence declined to September in both sexes corroborating the breeding season. 194

2 The percentage occurrence of males and females with gonads in various stages of maturity revealed that a distinct intensity as well as seasonality in the breeding activity was discernible. A major peak in gravid male and female number was recorded in October and November. Therefore fish abundance changes drastically according to the season. During the spawning month (November), absolute fecundity (AF) of L.thermalis ranged from 182 ova in a 21 mg ovary for a fish of 41 mm TL and 339 mg of body weight, to 3426 ova in a female of 1496 mg of body weight, 59 mm TL and 372 mg of ovary weight. The relative fecundity (RF) was 3742, and the mean number of ova per gram ovary was The mean diameter of a mature ovum was 0.56mm. The fish showed high fecundity, small eggs, and copious spawning. A positive linear relationship has been found to exist between fecundity and fish length, body weight, ovary length and ovary weight. The analysis of proximate composition of liver and ovary indicated that the ovary and hepatic lipids had an inverse relationship. A maximum amount of lipid was found in the gravid ovary. The glycogen and protein content of the liver decreased during the spawning period revealing their utilization during ovarian maturation. The minimum size at first maturity (Lp 50) for females was between 31 and 35 mm SL, and for males 26 and 30 mm SL, showing that males mature at a smaller size than the females. During spawning peak, the total length of mature males ranged from 35 to 61 mm that of females from 39 to 62 mm, and the body weight of mature males from 235 mg to 1153 mg, where as in females it was between 340 and 1496 mg per individual. The male: female ratio of random samples of L.thermalis examined every month showed that the two sexes were present in more or less equal numbers. The overall sexratio was 1:1, and there was no significant difference. 195

3 The gross morphology of the ovary of L.thermalis was typical with other teleostean ovaries. The morphological appearance of the ovaries examined throughout the year showed seven maturation stages in the ovarian cycle. The seasonal variation in GSI of various ovarian stages revealed that the development of the ovary was closely associated with the somatic growth. Histological examinations of ovaries from fortnightly samples enlightened the presence of nine stages of oocyte development characterized by specific cytological features, and oocyte and nuclear size. The monthly size-frequency distribution of oocytes in each stages of gonadal development enlightens the spawning season by the highest frequency of mature ova in October and November. There was a group-synchronous maturation of oocytes. The diameter of the mature ova ranged between 445 and 562 pm. The annual testicular cycle of L.thermalis showed five stages of development. The spermatogenic cycle also had five stages from spermatogonia to the spermatozoa. The percentage frequency of male and female L.thermalis of various stages of gonadal maturity in different TL groups during various seasons of the year also indicates the spawning season, which is characterized by the longest fishes. The analysis of gut contents of wild population of L.thermalis reveals that the natural food consists mainly of algae and other decaying organic matter found in the bottom sediments. The highest mean feeding rate on wet-weight basis was reported for the algal test feed containing only 20.36% protein. Conversion rate and feed growth ratio (FGR) were the highest for test feed containing 28.47% protein and followed by test feed with 26.19% protein. Assimilatory efficiency on dry weight basis was the highest for feed containing 35.72% protein, whereas relative growth rate (RGR) and net conversion efficiency (K2) were the highest for 28.47% protein feed. There was significant difference (P<0.05) in net conversion efficiency between size groups. Daily growth rate (DGR), protein 196

4 efficiency ratio (PER) and protein production value (PPV) were the highest in fish fed with % protein feed. The growth in dry weight of L.thermalis was best and more or less similar when fed on 28.47% protein feed and 35.72% protein feed. Carbohydrate is also equally important for growth, since it is an herbivore. Brooduish fed with 28.47% protein diet produced the highest average GSI value of The highest average ovary lengths and weights were attained in fish fed with diets containing 28.47% and 20.36% protein. L.thermalis fed with 20.36% protein diet containing the alga Spirogyra maxima had the highest absolute fecundity (974±63) followed by the fish fed with 28.47% protein diet (958±37). However there was no significant difference between the two diet groups. The diameter of mature ovum was not significantly different (P>0.05) between any diet groups. When L.thermalis were subjected to sublethal concentrations of ammonium chloride and ammonium sulphate, food consumption decreased with increasing concentrations of the toxicants, for the fish fed all the test diets. Food conversion ratio (FCR) increased (less efficient) with increase in the concentrations of both the toxicants, for all the test feeds, when compared to the control group. Daily growth rate (DGR) was significantly higher for test feed with 20.36% protein, indicating the thrivability of the fish by feeding the algal diet in a toxic medium. The length and weight of ovaries of female L.thermalis of all the five different test diet groups decreased significantly (P<0.05) on exposure to 0.20 mg/i of ammonia. Absolute fecundity was significantly affected in all diet groups, but significantly higher (P<0.05) in fish fed with 20.36% and 28.47% protein diets, under experimental conditions. Histopathological changes were observed in the ovary and testis of exposed fish. Several nuclear pathologies such as karyolysis, karyorrhexis, hypochromatinic nucleus and necrosis were found in the primary oocytes. Long-term ammonia exposure led to 197

5 loosening of oolemma, and hydrophic and vacuolar degeneration of vitellogenic oocytes in the ovaries of Lihermalis. In the testes of L.thermalis, nuclear pyknosis, cytokaryolysis and necrosis of spermatogonia, spermatocytes and spermatids, and drastic reduction in the number of spermatids and spermatozoa were the characteristic pathological observations. Conclusion It is inferred from a thorough analysis of the various reproductive traits and strategies of both male and female L.thermalis that it is a biannual monsoon breeder, having a major (October-November) and a minor (April-June) spawning seasons. The monsoon rains have been found to be one of the important factors influencing the reproductive activities of this fish. The females are bigger than males in all seasons. The group-synchronous and unimodal pattern of oocyte development in each spawning season shows that it sheds all the eggs at once in the spawning period itself. So it is iteroparous. Both of these breeding tactics conform to the general pattern of Indian freshwater teleosts. L.thermalis can be cultured in a large scale, using even low-protein diets, rich in carbohydrates, which are more than sufficient as feed for normal growth of the body. The costliest conventional protein source of fish meal could be replaced by cheap and locally available agricultural by-products, and that a 26-28% dietary protein level is optimal to attain maximum growth and efficient feed utilization by L.thermalis. Moreover, an algal diet is found to be more suited to achieve a better reproductive investment in terms of ovarian growth and fecundity, since L.thermalis itself is naturally an algal feeder. Because exposure of L.thermalis to ammonia affects food consumption, somatic growth, ovarian growth and fecundity, the presence of toxic metabolites or other chemical toxicants in the medium should be avoided for a prosperous aquaculture of 198

6 Lepidocephalus thermalis. The present study further supports the concept that the level and type of dietary components can greatly alter the biologic response of an animal under toxicant exposure. Recommendations The relationship between annual reproductive cycle and the changes in the gonadotropic activity of the pituitary may be studied by analysing the pituitary gonadotropin (GTH) content and the ultrastructure of the pituitary gonadotrophs, and the Hypothalamo-Pituitary-Gonadal Axis may be studied. Steroid formation in testes (Testosterone) and ovaries (Estradiol) can also be assayed in blood plasma and correlated with the annual reproductive cycle. The influence of exogenous factors on the endogenous endocrine glands should be analysed. The role of male and female sex pheromones in the courtship behaviour, mating and spawning may be studied. Induced breeding techniques can be adopted and experimentation done to evaluate a suitable technique, and also to know the possibility of large-scale seed production and during non-breeding seasons, and the ontogeny of L.thermalis may be studied. The types of enzymes present in the gut be analysed and thereby the nature of nutrient required by the fish be found out. In this way, still cheaper and crude form of diet could be formulated. 199

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