Probiotic-supplemented Groundnut-oil Cake as a Sustainable Fish Meal Replacement in Oncorhynchus mykiss Fingerling Diet: Effect on Growth, Feed Utilization, Whole Body Composition and Dry Matter Digestibility

A sixty-day feeding trial was conducted to evaluate the effects of replacing dietary fish meal with probiotic-supplemented groundnut-oil cake (pGNOC) on the growth performance and survival of Oncorhynchus mykiss fingerlings (average initial weight 5±0.2 g). Four isonitrogenous (45%) and iso-lipidic (16%) diets were formulated by, replacing 0% (Control, T0), 10% (T1), 20% (T2), and 30% (T3) of fish meal with pGNOC at inclusion levels of 0% (Control, T0), 10% (T1), 20% (T2), and 30% (T3). The pGNOC added to different diets contained a constant dosage of Lactobacillus acidophilus at 3×10⁷ CFU/kg diet. A total of 160 fingerlings were randomly randomly assigned to four treatments (4 replicates each) in 16 aquaria, with 10 fish per tankstocked in four treatments, each with four replicates (16 glass aquaria) with a stocking density of 10 individuals per aquarium. Fishes were fed twice daily at 5% of the body weight. No significant difference (P>0.05) was observed in terms of growth performance, whole-body composition, feed utilization and apparent dry matter digestibility between T1 and Control groups. However, increasing replacement levels beyond 10% adversely affected (P<0.05) these parameters. The survival rate, total erythrocyte count, and total leucocyte count indicated an insignificant variation (P>0.05) across all treatment groups. In conclusion, probiotic-supplemented GNOC, evaluated as a composite functional ingredient, can replace up to 10% of fish meal in the diet of rainbow trout fingerlings diets without any adverse effects on growth, feed efficiency and haematology.