Evaluation of growout diets with varying protein and energy levels for red drum (Sciaenops ocellatus)

The augmentation of nutrient retention and subsequent reduction of effluent waste generated by aquaculture production facilities are important factors in lowering production costs while simultaneously minimizing pollution and environmental impact resulting from intensive growout culture. Consequently, the present study was designed to evaluate the influence of dietary protein and energy levels on growth and nutrient utilization of the red drum in the initial stages of growout culture. Four practical diets were formulated to contain 44, 40, 36, and 32% protein with practical energy:protein (E:P) ratios. Additionally, the E:P ratio of the 44% protein diet was increased and the E:P ratio of the 32% protein diet was reduced. Each diet was fed to juvenile red drum (mean initial weight 50 g) to apparent satiation in triplicate tanks containing 670 l of seawater at 35 per thousand, 28.8 +/- 1.4 degrees C for 13 weeks. Significant differences (P < 0.05) in final weights, protein consumption, feed efficiency (FE), protein conversion efficiency (PCE) and intraperitoneal fat ratios (IPFR) were observed due to the dietary treatments. Weight gain and FE generally increased with protein and energy content of the diet. Increasing the lipid content of the 44% protein diet resulted in significantly higher FE values but also doubled the amount of fat deposited in the peritoneal cavity. Reduction of digestible energy from 335 to 279 kcal/100 g diet in the 32% protein diet did not significantly influence body composition or feed consumption. Based on regression analyses of feed consumption data, consumption rates appear to be primarily influenced by the weight of the fish and not the energy content of the diet. Consequently, reduced growth rate of fish offered the low protein feeds appear to be due to reduced protein intake and not imbalances in E:P ratios. These data indicate that red drum reared in seawater require at least 44% dietary protein (dry weight basis) for maximum growth and FE.