In a recent study, palatability was an issue, while fish meal (FM) was replaced by tuna by-product meal (TBM) in the diet of juvenile greater amberjack, Seriola dumerili. To address this issue, powdered salmon roe liquid (PSRL) was added to identify suitable feeding attractants for TBM-based diets.
A two-factorial experiment was designed to evaluate the potential for improving the palatability and use of TBM as a replacement for FM by supplementing the diet of juvenile greater amberjack with PSRL. The FM protein in the control diet (C) was partially replaced with TBM at levels of 25% (T25R0) and 40% (T40R0). The PSRL was then added at 5% and 10% to both the T25R0 and T40R0 diets, resulting in the formulations T25R5, T25R10, T40R5, and T40R10. The experiment was set in triplicate by stocking 30 juveniles (mean weight approximately 1.7 g) in each 500 L tank.
After a 6-week rearing period, 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. PSRL supplementation did not significantly enhance either palatability or feeding rate in TBM-based diets. Two-way ANOVA indicated that only FM replacement with TBM had a significant effect on the growth parameters mentioned above. A significantly lower whole-body crude lipid content was observed in all test diets compared to that of the C diet, resulting in significantly lower lipid retention efficiency in all test groups except T25R5 and T25R10. 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.