Development of a Practical Soy-Based Diet for White Seabass

Two feeding trials were conducted to begin development of a practical soy-based diet for white seabass Atractoscion nobilis. The first trial was designed to provide initial data on the efficacy of practical soy-based diets. Three diets and a commercial reference diet were evaluated. Research diets were 42% protein and 12% lipid, with varying protein sources: fish meal (FM), FM plus solvent-extracted soybean meal (SBM), or FM plus soy protein concentrate (SPC). Final weight (14.1-17.2 g), percent weight gain (307.2-401.8%), and feed conversion ratio (FCR; 1.0-1.2) followed similar trends, with fish offered the FM-based diet significantly outperforming the other dietary treatment groups. There was no significant difference between soy-based diets and the commercial reference diet, and no significant differences in survival due to dietary treatments were observed. The second trial was designed to evaluate varying levels of FM replacement with SPC in a series of four diets containing 42% protein and 12% lipid. The basal diet contained 40% FM and 24.6% SBM as primary protein sources. The FM was then reduced to 30, 20, and 15% of the diet using SPC as the replacement protein. Final weight (27.1-36.5 g), percent weight gain (69.0-116.6%), and FCR (1.5-2.4) followed similar trends, with performance decreasing as FM level was reduced. In general, each incremental reduction in FM resulted in significant reductions in final weight and percent weight gain and significant increases in FCR. Results from these initial trials on white seabass are encouraging because the poor response was most likely due to a nutrient imbalance or palatability problem, which can be corrected, as opposed to an allergic response. Given that the open formulations performed similarly to the commercial feed, these simple formulations can be used as a starting point for the development of practical diets for white seabass.