Comparison of Pond Production of Phase-III Sunshine Bass Fed 32-, 36-, and 40%-Crude-Protein Diets with Fixed Energy : Protein Ratios

—We stocked phase-III sunshine bass (white bass Morone chrysops /3 striped bass M. saxatilis ?) at a rate of 6,188 fingerlings/ha into twelve 0.04-ha earthen ponds supplied with continuous aeration. Three dietary treatments were randomly assigned to quadruplicate ponds. Sunshine bass were fed to apparent satiation once daily after average initial weight (mean 6 SE 1⁄4 214 6 5 g) and total length (245 6 1.6 mm) were determined. Diets were formulated to conserve the estimated digestible energy : crude protein (CP) ratio (9.3 kcal/g protein) and represented the following CP and energy values fed to fish: 32% CP (3,000 kcal/kg), 36% CP (3,360 kcal/kg), and 40% CP (3,760 kcal/kg). Harvest data suggest that nutrient density is a variable that can be manipulated to optimize production and reduce production costs. Production rates (mean 6 SE) were 2,851 6 600 kg/ha for the 32%-CP diet, 2,895 6 341 kg/ha for the 36%-CP diet, and 2,953 6 142 kg/ ha for the 40%-CP diet; production rates were not significantly different among dietary treatments. Survival was excellent and did not appear to be related to dietary treatment. Dressed (gilled and gutted) fish averaged 80% of whole-fish weight, and the dressed percentage did not vary as a function of nutrient density. Feed conversion ratios of 3.0 6 0.4, 2.8 6 0.2, and 2.6 6 0.1 were obtained for the fish fed 32-, 36-, and 40%-CP diets, respectively. Protein conversion ratios (mean 1⁄4 1.0) were not significantly influenced by dietary treatment. Feed cost increased with increasing dietary CP level; costs were US$0.447 per kilogram for the 32%-CP diet, $0.493 per kilogram for the 36%-CP diet, and $0.541 per kilogram for the 40%-CP diet. The resulting production costs attributable to feed were $1.34, $1.38, and $1.41 per kilogram of gain for the 32-, 36-, and 40%-CP diets, respectively. A savings of $0.16 per kilogram produced, or approximately $450 per hectare, was realized as a result of feeding either of the two lower-CP, lower-energy diets. Accordingly, we suggest that phase-III sunshine bass can be more economically produced by feeding diets as low as 32% CP with a minimum energy : protein ratio of 9.3 kcal/g CP. Production of sunshine bass (white bass Morone chrysops / 3 striped bass M. saxatilis ?) as a food fish continues to develop rapidly as an industry in the United States. Sunshine bass production consists of three phases: phase I (4-d posthatch larvae to ;1.0-g fingerling), phase II (;1.0-g fingerling to ;100-g juvenile), and phase III (;100-g juvenile to ;650-g market-size fish). The cost of feed generally represents one of the largest variable expenses incurred during intensive production of phase-III sunshine bass. Within that category, variations in levels and sources of dietary protein affect cost and production significantly. Therefore, the determination of the requirement for protein and the optimum energy to protein (E:P) ratio has been addressed repeatedly; however, the potential use of fixed amino acid profiles and E:P ratios has not received similar attention under intensive culture conditions with phase-III fish. Many diets used in production of sunshine bass are still formulated according to nutrient requirements for juvenile salmonids (NRC 1993). Such formulations are extremely energy dense with respect to adult sunshine bass requirements. It has been suggested that during phase III, sunshine bass may be reared on significantly lower amounts of dietary protein and energy than are indicated by results of previous research (Nematipour and Gatlin 1992a, 1992b; Brown et al. 1993; NRC 1993; Kasper and Kohler 2004). Requirements for protein and optimum energy : crude protein (CP) ratios (kcal of energy/g CP) have been evaluated in small sunshine bass (Sullivan and Reigh 1995; Webster et al. 1995); however, similar studies considering protein reduction as a result of fixing amino acid profiles and simultaneously reducing energy and that use phase-III fish have not been performed. Utilization of diets wherein similar amino acid profiles are maintained will probably provide for greater control than the use of diets with highly variable amino acid profiles, as is often the case in studies where the reduction of protein and/or energy is considered exclusively. Application of this formulation strategy may permit reductions in dietary protein while still maintaining optimal growth * Corresponding author: [email protected] Received April 21, 2005; accepted October 26, 2005 Published online June 12, 2006 264 North American Journal of Aquaculture 68:264–270, 2006 Copyright by the American Fisheries Society 2006 DOI: 10.1577/A05-044.1 [Article]