Optimization of macro-nutrient requirements and different protein-based ingredients for pengba, Osteobrama belangeri (Valenciennes, 1844) fingerlings

This research sought to ascertain the macronutrient requirements (protein, lipid, and carbohydrate) and to develop a cost-effective practical diet for Osteobrama belangeri fingerlings. Three experiments, lasting 90, 60, and 90 days respectively, were conducted in triplicate groups using flow-through FRP tanks with a water flow rate of 0.5 L/min. In Experiment 1, nine semi-purified diets with three levels of protein (30%, 35%, 40%; P30, P35, P40) and three levels of lipid (6%, 8%, 10%; L6, L8, L10) were tested. Results demonstrated that fish fed a diet with 35% protein and 8% lipid (P35/L8) showed significantly higher (p < 0.05) weight gain (WG), specific growth rate (SGR), and lower feed conversion ratio (FCR). In Experiment 2, optimum dietary carbohydrate levels were studied using six semi-purified diets containing 20%, 25%, 30%, 35%, 40%, and 45% carbohydrate, with fixed optimum protein and lipid levels (P35/L8). Results revealed that fish fed a diet containing 40% carbohydrates showed significantly higher (p < 0.05) WG, SGR, and lower FCR. Second-order polynomial regression analysis showed that the optimal dietary protein, lipid, and carbohydrate requirements for pengba fingerlings are in the range of 35.49–35.83%, 8.37–8.43%, and 39.61–40.23%, respectively. In Experiment 3, five practical iso-nitrogenous (35% protein), iso-lipidic (8%), and iso-caloric (4.0 kcal/g diets (D-1 to D-5) were formulated using various plant protein sources and fed to the fish. Among these, the D-5 diet, combining mahua oil cake with soybean and groundnut oil cakes, demonstrated significantly higher (p < 0.05) WG, protein efficiency ratio (PER), and FCR. The findings of the above three experiments provide a robust framework for the optimization of protein-rich ingredients for developing cost-effective practical diets to optimize the growth and nutrient utilization of O. belangeri fingerlings.