The immune responses and antioxidant status of Portunus trituberculatus individuals with different body weights

• Different sized Portunus trituberculatus were challenged with Vibrio alginolyticus.
• Immune response and antioxidant parameters' mRNA and protein levels were measured.
• Larger, compared to smaller, organisms had a better immune response capacity.
• Similarly, larger organisms had better antioxidant abilities.
• The parameters measured could be used as indicators of physiological status.

Vibrio alginolyticus is a virulent pathogen that affects crab aquacultures. In the present study, the immune responses and antioxidant status of big and small (based on body weight and size) 80-, 100- and 120-day-old specimens of Portunus trituberculatus, challenged for 72 h with Vibrio alginolyticus, were studied. The total hemocyte count (THC), and phagocytic, prophenoloxidase and phenoloxidase activities, of the big individuals (BIs) were higher than those of the small individuals (SIs) (P < 0.05). The antioxidant status of the organisms showed a similar pattern: superoxide dismutase (SOD) activity and glutathione/oxidized glutathione (GSH/GSSG) in the cell-free hemolymph and hepatopancreases of the BIs were higher than in the SIs (P < 0.05). There were no significant differences in α2-macroglobulin (α2-M), antibacterial and bacteriolytic activities in the cell-free hemolymph, or glutathione peroxidase activity in the cell-free hemolymph or hepatopancreas between the BIs and SIs. The α2-M and crustin gene expression levels in the hemocytes, and SOD expression in the hemocytes and hepatopancreas, were also significantly higher in the BIs. The results suggest that, compared with the SIs, the BIs possessed a higher resistance to V. alginolyticus infection.