Effects of Reduced Levels of Dietary Protein and Menhaden Fish Meal on Production,Dressout, and Biochemical Composition of Phase III Sunshine Bass Morone chrysops ♀× M. saxatilis ♂ Cultured in Earthen Ponds1

The responses of phase III sunshine bass Morone chrysops ♀× M. saxatilis ♂ to diets containing reduced levels of menhaden fish meal (30–10%, dry weight) and crude protein (40–36%, dry weight) were evaluated in two separate experiments. Reductions in fish meal were compensated by increase in dietary soybean meal, a meat and blood meal product, and additional amounts of a 1:1 catfish oil:menhaden oil mixture sprayed on as a top dressing. Fish were cultured in earthen ponds and fed commercially manufactured, extruded diets to apparent satiation. In Experiment 1, dietary crude protein was reduced from 40 to 36% and the menhaden fish meal ingredient was reduced from 30 to 15% (dry weight). The mean weight of fish stocked into each pond ranged from 144 to 188 g, the stocking density was 8641/ha, and the duration of the growout was 172 d. In Experiment 2, both dietary treatments contained 40% crude protein (dry weight) and either 30% or 10% menhaden fish meal. The mean weight of fish stocked into each pond ranged from 42 and 77 g, the stocking density was 8,500/ha, and the duration of the growout was 175 d. Simultaneous reductions in dietary menhaden fish meal and crude protein resulted in significant decreases in all production indices except survival and percent weight increase. Weights of filet, carcass, liver and intraperitoneal fat, expressed as a percent of total body weight, were not significantly different. A 66% reduction in dietary menhaden fish meal while the crude protein level was maintained at 40% did not significantly affect growth, production, and weights of filet, carcass, liver and intraperitoneal fat, expressed as a percent of total body weight, and represents a 6% decrease in the cost of feed. In both experiments, levels of protein, lipid, moisture, and ash of the whole body and the filet were not significantly different. Fatty acid composition of the filet and livers from fish fed the control and experimental diets in Experiment 2 were highly comparable. The comparable level of performance of fish fed diets believed to be deficient in HUFA suggests that the dietary levels reported to be required may not be totally applicable to diets formulated for pond culture.