*4.3. Effects of Aquaculture Mode on Nutrient Composition of Large Yellow Croaker*

It was generally accepted that muscle quality was a complex set of characteristics, mainly including muscle sensory properties, nutritional value, and freshness [36,37]. Among them, the nutritional value was the most concern. The nutritional value of fish muscle was measured by various components, such as protein and fat, as well as ash and moisture content [38]. This study showed that the nutrient composition of the muscle of the large yellow croaker cultured in ship was better than that of the cage, mainly due to the

higher protein and lower fat content. Due to the unique plasticity of skeletal muscle, it was prone to be seriously affected by exogenous factors. In the case of continuous swimming, important biochemical changes occurred in skeletal muscle, leading to changes in muscle nutrient composition [39,40]. There is a lot of research data showing that moderate exercise training can significantly improve the protein content of *Spinibarbus sinensis*, *Barbodes schwanenfeldi*, *Schizothorax prenanti*, and *Mylopharyngodon piceus*, and can also significantly reduce the lipid content of fish muscle [41–44]. It was also found in this study that large yellow croaker could keep swimming under stable flow field conditions (0.2–0.4 m/s), which was consistent with the phenomenon that was observed in the experiment. The cage was also located in the inner Bay Sea area, the water fluidity was poor, and difficult to form a continuous flow field. Therefore, flow velocity may be an important reason for the difference in muscle nutrient composition of the large yellow croaker. In addition, it was found in the experiment that the food intake of the large yellow croaker in the cage was low, and it failed to obtain enough nutrients to synthesize energy substances in the body, which may be another important reason affecting the nutrient composition of the large yellow croaker muscle.
