Dietary manipulations affecting growth and nitrogenous waste production ofred drum, Sciaenops ocellatus II. Effects of energy level and nutrient density at various feeding rates

Two experiments were conducted with red drum in recirculating, 110-1 aquari a to examine the effects of increasing dietary energy levels, and altering dietary energy and protein levels in conjunction with feeding rates on weig ht gain, body composition and ammonia production. Tn the first experiment, juvenile red drum(initially similar to 35 g) were fed diets containing 45% crude protein and 15.1 to 18.4 kJ estimated digestible energy/g for 6 weeks . In the second experiment, smaller (initially similar to 3.5 g) red drum w ere fed diets with digestible protein and digestible energy levels (DP/kJ) of 33/13, 40/15.5 and 50/18 at rates of 6, 5 and 4% of body weight (BW)/day , respectively, for 8 weeks. The 40/15.5 diet also was provided to apparent satiation. Each treatment was fed in triplicate and fish were weighed week ly to adjust feeding rates. Results from the first experiment indicated the re were no significant (P < 0.05) differences in weight gain or feed effici ency of red drum fed the various energy levels. However, intraperitoneal fa t deposition increased with an increase in dietary energy above 15.1 kJ/g, but no trends were evident in other body indices or tissue composition. Amm onia production, measured at 2-h intervals postprandial, was significantly reduced at 6-h post-feeding in fish fed the highest energy level. Plasma gl ucose and activities of enzymes involved in ammonia metabolism were unaffec ted by dietary energy levels. In the second experiment, weight gain did not differ significantly between fish fed diets containing 40 or 50% DP, but w as lower for fish fed the diet containing 33% DP, Fish fed the diet with le ast protein also had the lowest feed and protein efficiencies. While satiat ion feeding resulted in similar weight gain as feeding at a fixed rate, the efficiency of feed and protein utilization was improved with satiation fee ding. There were no cleat trends in body indices or ammonia production of f ish subjected to the various regimes. In conclusion, higher dietary energy levels did not improve growth, but did lower nitrogenous waste production o f red drum. Increasing dietary protein in conjunction with increasing energ y levels also improved growth and efficiency of feed utilization. (C) 2000 Elsevier Science B.V. All rights reserved.