Nutritional evaluation of protein isolate from neem seed cake in Labeo rohita (Hamilton, 1822) fingerlings concomitant with oil extraction processing industry

A protein isolate was prepared from the neem seed cake, a by-product of the oil extraction processing industry. With this, the study aimed to assess the effects of dietary neem seed protein isolate (NPI) on growth, nutrient utilization, physio-metabolic responses, and hepatic IGF-I expression of Labeo rohita fingerlings. Five isonitrogenous (270 g/kg crude protein as fed basis) and isocaloric (3800 kcal gross energy/kg as fed basis) experimental diets were formulated with graded level of NPI by replacing soy protein isolate (SPI) on protein equivalent basis. Thus experimental diets viz., control (0 g/kg NPI, 200 g/kg SPI protein), NPI-25 (56 g/kg NPI in replacement of 250 g/kg SPI protein), NPI-50 (110 g/kg NPI in replacement of 500 g/kg SPI protein), NPI-75 (164 g/kg NPI in replacement of 750 g/kg SPI protein), NPI-100 (217 g/kg NPI in replacement of 1000 g/kg SPI protein) were prepared for conducting the feeding trial. One hundred eighty acclimated Labeo rohita fingerlings (3.5. ? .0.2 g mean weight) were equally assigned to five experimental groups in triplicates following the completely randomized design. Fishes were maintained and fed twice daily to the satiation level during the experimental period of 60 days. The study results showed that percent weight gain, protein efficiency ratio, and feed conversion ratio were significantly (P < 0.05) affected by the dietary NPI in overall and linearly. Recorded values of these parameters in the control group were not significantly (P> 0.05) different from the treatment groups except for NPI-100, which showed a significant (P < 0.05) performance retardation. Hepato-somatic index and intestinal somatic index did not vary significantly (P> 0.05) among the experimental groups. A significantly (P < 0.05) higher apparent digestibility coefficients (ADCs) value for dry matter were found in NPI-25 group than all other experimental groups. However, the inclusion of NPI did not make any significant variation in intestinal amylase and lipase enzymes? activity though protease activity differed significantly (P < 0.05) in overall as well as linearly and quadratically. The growth regulatory gene IGF-I expression and RNA-DNA ratio of the treatment groups excluding NPI-100 exhibited a similar propensity with the control group, and showed a similar linear correlation with the growth performance. Hence, the study concludes that 750 g/kg of SPI protein at 200 g/kg inclusion level can be replaced with the inclusion of 164 g/kg NPI in the diet of Labeo rohita fingerlings while maintaining the analogous (P> 0.05) growth performances.