Evaluation of Experimental and Practical Diets for Walleye Stizostedion vitreum

Culture of walleye Sfizostedion vitreum is one of the largest components of public sector aquaculture in the eastern U.S. and there is increasing interest in private sector culture. However, the nutritional requirements of walleye are unknown and experimental diets for use in quantifying nutritional requirements have not been identified. We formulated four experimental and four practical diets and fed those to triplicate groups of walleye with an initial weight of 13 g per fish. The experimental diets contained either casein (CAS), casein + gelatin (CG), casein + arginine (CA), or casein + gelatin + crystalline amino acids (CGAA) as sources of amino acids. The practical diets were formulated to mimic salmon grower (SG) and trout grower (TG) diets, a fish meal‐free diet for trout (TFMF), and a walleye grower (WG) diet. Fish were fed twice daily to satiation for 9 wk. Feed consumption, percent weight gain, specific growth rates, feed efficiency, protein efficiency ratio, and protein retention efficiency were not significantly different among fish fed CGAA, SG, and TG, but those values were significantly higher than in fish fed other diets. Weight gain of fish fed CGAA was approximately 80% of that in fish fed SG and 91% of that in fish fed TG. Protein retention efficiency of fish fed CGAA was approximately 69% and 81% of that observed for fish fed SG, and TG, respectively. In general, the carcasses of fish fed diets CGAA, SG and TG had significantly lower moisture and ash concentrations, and higher lipid levels than fish fed other diets. There were no significant differences in carcass protein concentration, muscle proximate composition, or liver lipid concentration among treatments. Livers from fish fed all diets were characterized by microvesicular degeneration and glycogen accumulation in hepatocytes. Results from the study indicate that CGAA can be used as a basal experimental diet in future nutritional research with juvenile walleye and confirms the benefits of trout and salmon grower diets. Fish meal‐free diets formulated around the requirements for rainbow trout were consumed at approximately 80% of the values in fish fed TG and SG, but weight gain was approximately 20% of that in fish fed TG and SG. It appears the nutritional requirements for walleye are different than those of rainbow trout.