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

Abstract

We stocked phase‐III sunshine bass (white bass Morone chrysops ♀ × 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 ± SE = 214 ± 5 g) and total length (245 ± 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 ± SE) were 2,851 ± 600 kg/ha for the 32%‐CP diet, 2,895 ± 341 kg/ha for the 36%‐CP diet, and 2,953 ± 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 ± 0.4, 2.8 ± 0.2, and 2.6 ± 0.1 were obtained for the fish fed 32‐, 36‐, and 40%‐CP diets, respectively. Protein conversion ratios (mean = 1.0) were not significantly influenced by dietary treatment. Feed cost increased with increasing dietary CP level; costs were US.447 per kilogram for the 32%‐CP diet, .493 per kilogram for the 36%‐CP diet, and .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 .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.