Influence of dietary lysine levels on growth performance and protein metabolism in male Eriocheir sinensis under integrated rice-crab co-culture system

The Chinese mitten crab (E. sinensis) is valued in China for its high nutritional value. Due to the lack of specifically formulated feed, crab farming in Jilin Province, China, faces challenges of poor growth and low survival rates. Crabs were divided into five dietary lysine (Lys) level groups: 1.2%, 1.5%, 1.8%, 2.1%, and 2.3% (the analyzed dietary Lys concentrations were 1.19%, 1.50%, 1.78%, 2.07%, and 2.38% for groups Lys1, Lys2, Lys3, Lys4, and Lys5, respectively). From June to August, we investigated the effects of dietary Lys levels on growth performance and protein metabolism in male E. sinensis under an integrated rice-crab co-culture (RC) system. Results showed that the Lys4 group exhibited the highest weight gain rate (WGR) and specific growth rate (SGR) (P < 0.05). Muscle total amino acids (TAA) and essential amino acid (EAA) concentrations were highest in Lys2, whereas Lys concentration peaked in Lys3. The essential-to-total amino acid ratio (EAA/TAA) was maximized in Lys4 (P < 0.05). Gonadal crude fat content peaked in Lys2, whereas crude protein reached its maximum in Lys3 (P < 0.05). Hepatopancreatic crude fat content was highest in Lys4 (P < 0.05). Protein metabolism–related enzymes differed significantly: alkaline phosphatase (AKP) activity was highest in Lys3, while acid phosphatase (ACP) peaked in Lys2. Superoxide dismutase (SOD) and γ-glutamyl transferase (γ-GT) activities were significantly elevated in Lys4 (P < 0.05). Aspartate aminotransferase (AST) activity was significantly increased in Lys3 (P < 0.05). Adenosine deaminase (ADA) activity was also significantly elevated in both Lys3 and Lys4. Total carnitine content peaked in Lys3. Based on these findings, the optimal dietary Lys level for E. sinensis in the RC system is recommended at 1.78–2.07%.