author(s)
Md. Zulfikar Ali, Mritunjoy Paul, Prasanta Jana, Md. Khalilur Rahman and Yahia Mahmud

abstract
A 60 days feeding trial was conducted to investigate the optimum dietary protein to energy ratio (P/E ratio) in Sutchi catfish Pangasianodon hypophthalmus. The same aged uniform size fingerlings of P. hypophthalmus were randomly distributed into groups of 40 fish (averaging 2.55 ± 0.05g in weight) per 70-L fiber glass tank in triplicates following completely randomized design. Six experimental diets were formulated to contain two levels of crude protein (25 and 30%) and three lipid levels (5, 10 and 15%) formed 25/5, 25/10, 25/15, 30/5, 30/10 and 30/15% P/E ratio contained 15.50, 17.36, 19.38, 16.52, 18.38 and 20.35 kJ g^-1 gross energy. Feeding rate and frequency were 10-8% of their body weight 3-2 times daily. The highest (P<0.05) weight gain was observed for fish consuming that diet which contained 30/10% P/E ratio. The optimum dietary P/E ratio found for P. hypophthalmus fingerlings is 16.33 mg protein kJ^-1 of GE, for a diet containing crude protein 30%, crude lipid 10% and gross energy 18.38 kJ g^-1. Significantly indifferent (P>0.05) values of protein utilization were found in-between the both (higher and lower) protein diets. Higher lipid deposition (P<0.05) in whole body and liver was observed with increasing dietary lipid level at each protein diet and as higher (P<0.05) for the lower protein diets. Significantly (P<0.05) lower liver glycogen level was found with increasing dietary lipid at each protein level. No significant (P>0.05) difference was found in digestive enzyme activities (amylase, protease and lipase) in fish fed with different experimental diets. Hence, it may be concluded that Sutchi catfish P. hypophthalmus performed best the diet containing 30%, 10%, 18.38 kJ g^-1 and 16.33 mg protein kJ g^-1 GE protein, lipid, gross energy, and P/E ratio, respectively.