Fish performance, fillet characteristics, and health assessment index of rainbow trout (Oncorhynchus mykiss) fed diets containing adequate and high concentrations of lipid and vitamin E

The recent trend for rainbow trout feeds to be higher than 15% lipid may improve feed conversion ratios (FCRs) and increase the lipid concentration of the fish. However, one disadvantage of the higher lipid concentration in fish is the potential for increased rates of lipid oxidation, which could affect fish health and contribute to off-flavors in fillets. The objective of this experiment was to determine the effects of adequate and high concentrations of dietary lipid and the antioxidant vitamin E on fish performance, fish health, and fillet product quality of rainbow trout. A 10-week feeding trial was conducted with diets containing either 15 or 30 g lipid/100 g feed, and either 300 (e) or 1500 (E) mg dl-α-tocopheryl acetate/kg feed (15e, 15E, 30e, and 30E). Fish fed 30% lipid diets had significantly higher final body weight, specific growth rate (SGR), and protein efficiency ratio (PER) than fish fed 15% lipid diets. All health parameters of fish measured in the experiment were within normal ranges of healthy fish although several parameters were affected by increasing dietary lipid concentration. Lipid concentration in fish body (whole body, fillets, and viscera) reflected dietary lipid concentration. Increasing the lipid concentration in the feed from 15% to 30% increased the fillet lipid concentration from 8.4 to 9.6 g lipid/100 g fillet. Vitamin E concentrations in fillets reflected dietary vitamin E concentration and ranged from 8.3 mg/kg (30e) to 49.1 mg/kg (15E) (P<0.05). Fish fed the 30% lipid diets had significantly higher concentration of malonaldehyde [thiobarbituric acid reactive substances (TBARS)] in fillets than fish fed the 15% lipid diets, and fish fed the “E” diets had significantly lower concentration of malonaldehyde in fillets than fish fed the “e” diet. Principal components analysis of sensory evaluation results showed that the 30e fillet had higher scores than other treatments on a “fishy” axis, which was highly correlated with overall flavor intensity, fishy, musty, sour, and bitter attributes. “Fishy” scores of the 30E fillets were lower than the 30e fillets, and were comparable to those of the 15e fillets. These results suggested that increasing the concentration of vitamin E in the feed from 300 to 1500 mg/kg could reduce the “fishy” aroma in fillets of trout fed a 30% lipid diet.