Abstract
The breeding biology, embryonic development, larval rearing and pond culture of endangered freshwater eel (Tarabaim), Macrognathus aculeatus (Bloch) were studied at the Field Laboratory Complex of Bangladesh Agricultural University, Mymensingh during April, 2005 to March, 2008. The fecundity of M. aculeatus was estimated by gravimetric method and a highly significant (P<0.01) linear relationship was found to exist between fecundity and gonadal weight. The equation was obtained to be: Y 503.77x+20.635. The value of co-efficient of determination (R2) was 0.998. Four sources of hormonal substances were tested to evaluate their efficacy on ovulation, fertility and hatching rate of M. aculeatus eggs under controlled conditions. Double doses of PG (1st 40 mg/kg body wt., 2nd 50 mg/kg body wt.) and HCG (1st 950 IU/kg body wt., 2nd 1800 IU/kg body wt.) was found to be better than single dose of ovaprim (4 ml/kg body wt.) in egg maturation and ovulation. Profasi and ovaprim were found comparatively less respondent to ovulation. Embryonic and larval developments of M. aculeatus were studied under laboratory conditions. At fertilization, the eggs were 0.8 mm in diameter. First cleavage was recorded within 0.45 hrs after fertilization and the embryonic rudiments of developing eggs appeared at 18 hrs and 20 minutes at 27.0-32.5°C. The yolk sac was completely absorbed at 72 hrs during embryonic development on attainment of 6.0 mm total length. At the same time, digestive system became fully developed and the larvae were started to search for food. Nursery rearing of M. aculeatus was studied in relation to different supplementary feed and varying stocking densities for a period of six weeks in earthen ponds. The growth performances of Tarabaim (ADG, SGR and survivality rate) were found to be better at a stocking density of 0.7 million individual/ha when fed diet prepared with a mixture of mustard oil cake (20%), rice bran (33%), wheat bran (25%), fish meal (20%), vitamin premix (1%) and dicalcium phosphate (1%) than other diets. Stocking density had significant effect on the growth, survival and production of fish fry. The physico-chemical and biological characteristics of water were found to be in optimum ranges for the fish culture. Macrognathus aculeatus when stocked (initial at 2.5g) at 24700/ha in monoculture yielded 2671.31 kg/ha/6 month, with net return of Tk. 65291/- with food conversion ratio of 3.23. Production potential of M. aculeatus in the monoculture system were examined. The technology of monoculture system indicated that the cultivation of this cel was economically viable and the growth rate of M. aculeatus was higher in open water system.