A 6-week feeding trial evaluated composite protein mixtures as partial replacements for fish meal (FM) in diets for juvenile yellowtail (Seriola quinqueradiata). Five diets were prepared: a control diet (C) with FM as the main protein source, and four test diets in which 25% and 35% of FM protein were replaced by either a composite mixture of SSM (44% shark by-product meal + 56% surimi by-product mixture; SS25 and SS35) or SMM (58% shark by-product meal + 42% other by-product mixture; SM25 and SM35). Fish (initial mean weight 0.85 g) were stocked at 30 fish per 500-L tank, with three replicate tanks per treatment. Growth performance indicators, including final mean weight, percent weight gain, specific growth rate, daily feeding rate, and survival, did not differ significantly among treatments (p > 0.05). Feed efficiency was significantly higher in SS25 and SS35 than in the control (p < 0.05), whereas no significant differences were observed among the by-product-based diets. Whole-body proximate composition was unaffected, except for crude ash. The levels of key n-3 fatty acids, eicosapentaenoic acid and docosahexaenoic acid, were significantly lower in SM25 and SM35 than in the control (p < 0.05). These results indicate that up to 35% of FM protein can be replaced with shark by-product-based mixtures without compromising growth in juvenile yellowtail.

A six-week feeding experiment was carried out to investigate the suitability of wasted tofu meal (WTM) as a substitute protein source for fish meal (FM) in diets for juvenile yellowtail (Seriola quinqueradiata). A diet containing FM as the principal protein source served as the control (C), while WTM was incorporated to replace 20%, 35%, and 50% of the FM protein in the experimental diets, referred to as T20, T35, and T50, respectively. Juvenile fish with an initial average body weight of approximately 30.99 g were randomly distributed into 500-L tanks at a density of 20 fish per tank, with triplicate groups assigned to each dietary treatment. At the end of the feeding trial, fish fed the T20 diet showed no significant differences from the control group in final body weight, specific growth rate, daily feed intake, feed efficiency, or survival. However, fish receiving the T35 and T50 diets exhibited significant reductions in most growth performance indices compared with those fed the control diet. Although nutrient retention efficiency and plasma biochemical indicators associated with fish health were not significantly influenced by dietary treatment, alterations were observed in whole-body lipid composition and fatty acid profiles, including reductions in EPA, DHA, total n-3 fatty acids, and the n-3/n-6 fatty acid ratio with increasing WTM inclusion. Overall, the findings suggest that, under the dietary formulations tested, WTM can replace up to 20% of FM protein in diets for juvenile yellowtail without negatively affecting growth performance or physiological health; however, supplementation with n-3 HUFA-rich lipid sources may be required to maintain optimal whole-body fatty acid composition and product nutritional quality.

A two-factorial experiment was conducted to evaluate the potential for improving the palatability and utilization of tuna by-product meal (TBM) as a replacement for fish meal (FM) via supplementing the diet of juvenile greater amberjack (Seriola dumerili) with powdered salmon roe liquid (PSRL). FM protein in the control diet (C) was partially replaced with TBM at levels of 25% (T25R0) and 40% (T40R0). PSRL was then added at 5% and 10% to both the T25R0 and T40R0 diets, resulting in the formulations T25R5, T25R10, T40R5, and T40R10. After a 6-week rearing period, during which groups of 30 juveniles (mean initial weight of approximately 1.7 g) were stocked in 500 L tanks, there were no significant differences in the final mean weight, weight gain, or specific growth rate among fish fed diets C, T25R0, and T25R5. However, the other experimental diets showed significantly lower values compared to the C diet (p < 0.05). PSRL supplementation did not significantly enhance either palatability or feeding rate in TBM-based diets (p > 0.05). Two-way ANOVA indicated that only FM replacement with TBM had a significant effect on the growth parameters mentioned above (p < 0.05). A significantly lower whole-body crude lipid content was observed in all test diets compared to that in the C diet, resulting in significantly lower lipid retention efficiency in all test groups except T25R5 and T25R10 (p < 0.05). These results suggest that 25% of FM protein can be replaced with TBM protein in the diet of juvenile greater amberjack, but PSRL does not effectively address the palatability issues associated with TBM-based diets.