Inclusion level of deoiled rice bran (DORB) in the diet of Labeo rohita (Hamilton, 1882) fingerlings: Effect on growth and gene expression of IGF-I and IGF-II

A 60-day feeding trial was conducted to evaluate the effect of deoiled rice bran (DORB) on the growth performance and liver IGF-I and IGF-II mRNA expression in a freshwater fish, Labeo rohita. Six isonitrogenous (30%), isolipidic (6%) and iso-energetic (1.8 MJ/100 g) diets were prepared with different inclusion level of DORB viz., C (control, 0%), T20 (20%), T30 (30%), T40 (40%), T50 (50%) and T60 (60%). Three hundred and fifteen (315) fingerlings with 15 fish per tank having an average weight of 8.0 +/- 0.5 g were randomly distributed in seven treatments in triplicates following a completely randomized design. At the end of the experiment, growth and nutrient utilization were evaluated in terms of weight gain% (WG %), SGR, FCR, PER, RNA/DNA ratio along with the gene expression of IGF-I and IGF-II. The weight gain % and specific growth rate were similar in 30, 40, 50 and 60% DORB fed groups, but higher (p < 0.05) than the control and commercial diet fed groups. The PER (Protein Efficiency Ratio), LER (Lipid Efficiency Ratio) and FCR (Feed Conversion Ratio) were similar (p > 0.05) in 30, 40, 50 and 60% DORB fed groups. The RNA-DNA ratio was significantly lower in T50 group, which was similar to T60 group. Based on second order polynomial regression analysis (y = - 0.008x(2) + 0.5227x + 1.3407, R-2 = 0.91), the expression of IGF-I was found to be maximum at 33% inclusion level. The hepatic IGF-I and IGF-II gene expression were checked using real time PCR normalised against the beta-actin gene and found to be maximum at the dietary inclusion level of 33%. Hence, from these results it can be concluded that though growth rate was similar in all the groups fed with DORB at 30 to 60% of inclusion level, but an optimum inclusion level of DORB at 33% is best to support the nutrient utilization and growth performance of Labeo rohita fingerlings based on gene expression of IGFI and IGF II in liver.