Effects of Dietary Protein Levels on Growth, Digestive Enzyme Activity, Antioxidant Capacity, and Gene Expression Related to Muscle Growth and Protein Synthesis of Juvenile Greasyback Shrimp ( Metapenaeus ensis )

An 8-week feeding trial was conducted to assess the effects on growth, antioxidant capacity, digestive enzyme activity, and gene expression related to muscle growth and protein synthesis of juvenile greasyback shrimp ( ) using five experimental diets containing 29.37%, 34.30%, 39.11%, 44.05%, and 49.32% of protein. The results demonstrated that juvenile greasyback shrimp consuming 39.11%, 44.05%, and 49.32% dietary protein had a significantly higher final body weight (FBW), weight gain (WG), feed conversion ratio (FCR), and specific growth rate (SGR) than other groups ( < 0.05). The protein efficiency ratio (PER) showed a significantly quadratic pattern with increasing dietary protein levels < 0.05). The highest trypsin and pepsin activities were observed in the group with a protein level of 44.05% ( < 0.05). Relatively higher superoxide dismutase (SOD) activity was found in groups with protein levels of 39.11% ( < 0.05). Alkaline phosphatase (AKP) and catalase (CAT) activity showed a significantly linear increasing pattern with increasing protein intake up to 44.05%, and then decreased gradually ( < 0.05). Compared to the dietary 29.37% protein level, the expression levels of myogenic regulatory factors ( , , and ) and mTOR pathway ( , , , and )-related genes were significantly up-regulated in muscle with 39.11%, 44.05%, and 49.32% dietary protein levels ( < 0.05). The AAR pathway ( , , and )-related gene expression levels were significantly lower in muscles with 39.11%, 44.05%, and 49.32% protein levels than in other groups ( < 0.05). Based on the broken-line regression analysis of SGR, the estimated appropriate dietary protein requirement for juvenile greasyback shrimp is 38.59%.