Effects of fish meal replacement with compound protein source on growth performance and body composition of juvenile Japanese Seabass <i>Lateolabrax japonicus</i>

Abstract Objective To evaluate compound protein sources (CPSs) as a sustainable alternative to fish meal in diets for juvenile Japanese Seabass Lateolabrax japonicus, assessing impacts on growth performance and body composition. Methods A dietary CPS was formulated by blending soybean meal, meat and bone meal, peanut meal, and rapeseed meal (4:3:2:1 ratio), supplemented with crystalline L-methionine (0.77%), L-lysine (0.95%), and L-isoleucine (0.44%). Six isoenergetic diets with graded fish meal replacement (0, 13, 26, 39, 52, 65%) were prepared. Juvenile Japanese Seabass (n = 180 per group, initial weight 6.26 ± 0.10 g) were reared in triplicate sea cages per diet and fed for 8 weeks. After 24-h fasting, fish were bulk-weighed per cage. Subsequently, 20 fish per replicate were euthanized with MS-222 (100 mg/L) and stored at −20°C for whole-body composition analysis. Results The findings demonstrated that the replacement levels of 39, 52, and 65% were considerably lower than those of the other three groups (P &amp;lt; 0.05) in terms of weight gain, specific growth rate, and feed efficiency. Dietary CPS supplementation resulted in a decrease in whole-body crude protein and crude lipid and gross energy contents. The dietary CPS level had a substantial impact on whole-body lysine and methionine levels (P &amp;lt; 0.05), while other essential amino acid contents did not differ significantly. Conclusions A dietary CPS effectively replaces up to 26% of dietary fish meal without compromising production metrics, providing a viable strategy to enhance aquaculture sustainability.