In recent years, the search for potential alternatives to fish meal (FM) has been a global issue due to the shortage of supply, and price surge of FM. Although several sources of protein from plant-based and animal by-products have been used in different species, there are several limitations in some of those products and the availability is species-specific. Therefore, it is necessary to continue to look for more reliable alternative protein sources. Although the availability of tuna by-product meal (TBM) has been determined in different species, as far as we know there is no report on this aspect in the greater amberjack, Seriola dumerili. Hence, the availability of TBM as a replacement of FM in the diet of juvenile greater amberjack was investigated from its effect on growth, mercury (Hg) levels in fish whole-body, phosphorus (P) load in the ecosystem, and plasma chemistry.
FM was the main protein source in the control diet (C), and FM protein in C was replaced by TBM at 25%, 50%, 75%, and 100% to formulate the diets TM25, TM50, TM75, and TM100, respectively. The experiment was set in triplicate by stocking 30 juveniles (mean weight about 6.7 g) in each 500 L tank.
After a 42-day rearing period, there were no significant differences in growth, nutrients digestibility and productive value between diets C and TM25. However, the quadratic polynomial regression analysis suggests that the optimal dietary levels of TBM against final weight is 14.5%. A significant linear correlation was found between Hg in diet and fish whole-body, but the level was much lower to pose health risk to humans. Due to a lower intake of P from TBM-based diets, P load was significantly reduced compared to the control group. Plasma levels of total protein, total cholesterol and albumin in diets TM75 and TM100 were significantly lower compared to those of diets C, TM25 and TM50. The results suggest that 14.5% of FM protein can be replaced by TBM in the diet of the juvenile greater amberjack and that a significant reduction in P load can be achieved from the TBM-based diet.