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Two 8‐wk feeding trials were conducted with juvenile red drum to determine the maximum levels of soybean meal that may replace fish meal in diets containing 38% crude protein, without reducing weight gain. In the first experiment, fish fed diets containing up to 90% of the protein from soybean meal gained as much weight as fish fed a diet with 100% of protein from fish meal, but fish fed the diet with 100% of its protein from soybean meal gained significantly (P < 0.05) less. Supplementation of glycine and fish solubles individually at 2% (as‐fed basis) in diets containing 90% of their protein from soybean meal tended to increase weight gain of fish compared to those fed a similar diet without supplementation. Similar results were obtained in the second experiment, as fish fed diets containing 90% of their protein from soybean meal gained as much weight as fish fed a diet with 100% of its protein from fish meal. Fish fed diets with 95% and 100% of their protein from soybean meal gained significantly less weight than those fed the diet with all of its protein from fish meal. Supplementation of glycine at 2% in the diet containing 95% of its protein from soybean meal significantly improved weight gain of fish relative to those fed a similar unsupplemented diet. Supplementation of fish solubles at 5% of diet on a dry‐matter basis provided a nonsignificant increase in weight gain compared to that of fish fed a similar unsupplemented diet. In both experiments there was greater observed consumption of the soybean‐meal‐based diets than diets with all of their protein from fish meal. A minimum of 10% of protein from fish meal appears necessary in practical diets containing most of their protein from soybean meal to prevent impaired growth and feed efficiency of red drum.

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Precise formulation of diets that meet but do not greatly exceed nutritional requirements should assist in lowering feed costs for commercial aquaculture of red drum, Sciaenops ocellatus. In this study, protein and energy requirements of red drum for maintenance and maximum gain were determined by feeding a diet containing digestible protein (DP) at 36.5% and 14.2 kJ digestible energy (DE) per gram at various rates for 8 wk in two separate experiments. Changes in weight and whole-body energy and protein were measured and regressed against protein or energy fed using a nonlinear procedure. In the first experiment, juvenile fish [ approximately 3. 4 g initial body weight (BW)] were either starved or fed at one of the following g/(100 g BW.d): 0.5, 1, 2, 4, 6, or 8. The second experiment utilized larger red drum (approximately 5.5 g initial weight), fed 0.75, 1.5, 3, 5, 5.5, 6, 6.5 or 7 g/(100 g BW.d) to confirm and refine results from the first experiment. Based on maintenance of body weight in both experiments, red drum had a protein maintenance requirement of 1.5 and 2.5 g DP/(kg BW.d) whereas estimates based on maintenance of whole-body protein were 0.5 and 2.2 g DP/(kg BW.d). Energy requirements for maintenance of weight and body energy ranged from 58 to 93 and 92 to 97 kJ DE/(kg BW.d), respectively. Protein requirements for maximum weight gain and change in body protein ranged from 20 to 25 g DP/(kg BW.d), whereas energy requirements for maximum weight gain and whole-body deposition ranged from 776 to 958 and 914 to 985 kJ DE/(kg BW.d), respectively. These requirements for maintenance and maximum gain of red drum should assist in formulation of diets for a variety of desired feeding strategies.