Dietary effects of protein and lipid levels on growth performance and flesh quality of large-size largemouth bass (Micropterus salmoides)

Abstract

The aim of this trial was to investigate the effects of dietary protein and lipid levels on growth performance and flesh quality of largemouth bass (Micropterus salmoides). A 3 × 3 two-factor design was used, including three crude protein levels of 46%, 50%, 54% (P46, P50, P54) and three crude lipid levels of 8%, 12%, 16% (L8, L12, L16). Thus, a total of nine diets (P46/L8, P46/L12, P46/L16, P50/L8, P50/L12, P50/L16, P54/L8, P54/L12 and P54/L16) were prepared and fed to large-size largemouth bass with initial body weight of 109.7 g for 84 days. At the same dietary protein level, weight gain rate (WGR), protein efficiency rate (PER), viscerosomatic index and polyunsaturated fatty acids (PUFAs) percent in flesh showed an increasing trend with increasing the dietary lipid level, while feed conversion ratio (FCR) showed a decreasing trend. At P46 and P50, whole fish crude protein, muscle crude protein, total collagen content, hardness, springiness, chewiness and shear force increased, and steaming loss and freezing loss decreased with increasing the dietary lipid level, while the above indicators showed an opposite trend at P54. At P50, the protein retention (PR) of 16% crude lipid group was significantly higher than that in the 8% and 12% crude lipid groups (P < 0.05). At the same dietary lipid level, the 50% and 54% crude protein groups presented higher WGR and lower FCR than the 46% crude protein group. The P54/L16 group had the highest WGR (184.4%) and lowest FCR (0.92) among all the groups, but the P50/L16 group presented similar WGR and FCR to the P54/L16 group (P > 0.05). The P50/L16 group showed the highest PER, PR, whole fish protein, muscle protein, total collagen, PUFAs, muscle hardness, springiness, chewiness, shear force and the lowest steaming loss. In conclusion, based on growth performance and flesh quality, the appropriate dietary protein and lipid requirements for large-size largemouth bass were 50% and 16%, respectively.