The effects of hairtail protein hydrolysate-Fe2+ complexes on growth and non-specific immune response of red swamp crayfish (Procambarus clarkii)

The experiment was conducted to investigate the effects of prepared hairtail protein hydrolysate-Fe2+ (PH-Fe2+) complexes on growth and non-specific immune responses of crayfish (Procambarus clarkii). The diets with five different levels of PH-Fe2+ (200, 400, 600, 800, and 1000 mg/kg) were fed to crayfish for 60 days. The results indicated that the survival rate, weight gain percentage, specific growth rate, and muscle index of crayfish with 400-1000 mg/kg of PH-Fe2+ feeding were significantly higher, 9.94-10.10, 8.55-8.72, 0.24-0.29 %/day, and 2.39-3.05 %, respectively, than the control values after 60 days of feeding. Additionally, after 30 days of feeding, 200-400 mg/kg of PH-Fe2+ showed no significant (P > 0.05) improvement effect on activities of superoxide dismutase (SOD), phenoloxidase (PO), lysozyme (LSZ), and acid phosphatase (ACP) in serum or hepatopancreas of crayfish. However, significant improvement effects were observed in 800-1000 mg/kg groups. After 60 days of feeding, 400-600 mg/kg of PH-Fe2+ significantly (P < 0.05) improved the activity of SOD and LSZ, but did not affect the activity of PO and ACP significantly (P > 0.05). Moreover, the activities of SOD, PO, LSZ, and ACP in serum and hepatopancreas were all significantly enhanced upon treatment with 800-1000 mg/kg of PH-Fe2+. For these reasons, PH-Fe2+ can be recommended as a supplement in crayfish feed to increase the growth and immunity.