Growth, nutrient retention, innate immune response, and intestinal morphology of juvenile, soy-naïve hybrid striped bass, Morone saxatilis x M. chrysops fed commercial-type, soy-based, ideal protein, fish meal replacement diets

To develop plant-based diets for hybrid striped bass (HSB), Morone chrysops × M. saxatilis, we evaluated six soy products in extruded, ideal protein, fish meal (FM) replacement diets fed to soy-naïve juveniles (3.72 ± 0.01 g initial weight) for up to 5 months. The products included soy protein concentrate (SPC), a conventional soybean meal (SBM) from Archer Daniels Midland (ADM), three non-genetically modified (non-GM) soybean varieties from the University of Arkansas (R05–1415, R05–1772, and R07–2001) with high protein and putatively reduced anti-nutritional factor (ANF) content, and Ozark soybeans, parent to the non-GM strains. The control diet included Special-Select® menhaden fish meal (MFM-S; Omega Protein) at 25.5% of diet and contained 40% digestible protein (DP) and 16% lipid. MFM-S was replaced by each soy product on a digestible protein basis and supplemented with Met, Lys, and Thr based on 40% HSB muscle AA profile. HSB sac fry were reared on soy-free diets to increase the likelihood of detecting any soy-induced performance issues when they were fed the test diets to satiation twice daily. Daily feed intake did not differ among treatments (2.2–2.5% of body weight/day). Fish fed the ADM diet were larger (58 g) and gained (1465%) more than those fed the control (51 g, 1251%); otherwise final weights (47-54 g) and weight gains (1153%–1355%) did not differ from the FM control. Gains in fish fed the SPC diet fell below those of fish fed the ADM, Ozark, and R0–1415 diets. Feed conversion ratios (FCR) were slightly poorer for fish fed the R05–1772 diet (1.09) compared to those fed the control (0.93); otherwise, FCR (0.97–1.01) did not differ among diets. The following responses also did not significantly differ among treatments: protein, energy, and AA retentions, whole body protein, moisture, and ash, muscle ratio, and hematological and innate immune parameters. There were slight differences among treatments in whole body lipid and energy, Glu and His content, and liver size. Challenge with Columnaris generally revealed no adverse effect of soy diet on time to death. In contrast to most fish studies, moderate inflammation was noted in proximal intestinal samples from soy-based diets after 73 days, whereas distal gut morphology did not differ among diets. However, no intestinal inflammation was found after a further 5 months of feeding test diets. Complete replacement of FM with various soybean varieties is possible in juvenile hybrid striped bass diets using ideal protein formulas with little impact on fish performance.