Evaluation of Optimal Dietary Protein Levels and Meat Quality of Adult Hybrid Abalone (haliotis Discus Hannai♀ × H. Fulgens♂) under Two Representative Water Temperatures

In this study, the optimal dietary protein levels for adult hybrid abalone (H. discus hannai & FEMALE; x H. fulgens & MALE;) were evaluated at two representative temperatures, and the interactive influences of dietary protein and water temperature on abalone meat quality were examined. Six isoenergetic and isolipidic diets containing graded levels of protein (15%, 20%, 25%, 30%, 35%, and 40%) were fed to the hybrid abalone for 90 days. Based on the specific growth rate, the optimum dietary protein levels for adult hybrid abalone using a quadratic curve model were estimated to be 28.07% and 26.47% of the diet at 23 degrees C (optimum temperature) and 27 degrees C (high temperature), respectively. The amount of crude protein in the abalone body increased linearly with the dietary protein levels and water temperature. Antioxidation enzyme activities of abalone muscle, including GPx and GST were significantly affected by the interaction of dietary protein levels and water temperature. As for texture analysis, the abalone kept at 23 degrees C exhibited higher meat hardness than those fed the same diets at 27 degrees C. The n-3 PUFAs (particularly DHA and EPA) in abalone meat were significantly influenced by dietary protein levels, and the highest content was observed in the 30% dietary protein group. These levels were not affected by water temperature. In addition, higher dietary protein levels and water temperatures increased the total contents of free amino acids and flavor amino acids (Asp + Glu + Gly + Ala + Arg + Tau). The cooking loss of abalone meat was reduced with increased protein levels and was significantly lower in the 23 degrees C group, along with a higher meat postmortem pH value. The collagen fiber ratio and collagen content of abalone meat were higher in the 23 degrees C group. In summary, for multiple diet feeding strategies in practical production of abalone aquaculture, the balance between the seasonally specific feeds cost benefits and the abalone meat quality should be carefully evaluated.