Enhancement of non-specific immune responses in common carp,Cyprinus carpio, by dietary carotenoids obtained from shrimp exoskeleton

Abstract

The immunostimulatory role of carotenoid extract from shrimp processing discards was evaluated by feeding common carp fingerlings with a diet containing carotenoid extract for 21 weeks at 100 and 200 mg kg�1 astaxanthin levels. Haemoglobin content was significantly (P < 0.05) higher in the blood of fish fed with carotenoid diet (>8.1 g dL�1) compared with that from fish fed with carotenoid deficient diet (6.86 g dL�1) and also leukocyte counts were higher (P < 0.05). No differences (P > 0.05) were observed in total serum protein, globulin level and albumin-globulin ratio, but albumin content was higher (P < 0.05). Respiratory burst activity was significantly (P < 0.05) higher, the serum lysozyme activity almost doubled and the serum bactericidal activity was significantly increased when the fish were fed with diet containing 200 mg kg�1 of astaxanthin but no significant differences were observed in serum trypsin inhibitory activity. There was a significant (P < 0.05) increase in leukocyte myeloperoxidase activity due to dietary carotenoids. Challenging fish with Aeromonas hydrophila after the feeding period resulted in 50% mortality in the control group while in the group fed with diet containing 100 mg kg�1 astaxanthin, the mortality rate was 15%. No mortality and even symptoms of infection was not observed in the group fed with diet containing 200 mg kg�1 of astaxanthin. The study indicated that carotenoid extract from shrimp processing discards can effectively be used as immunostimulants in aquaculture of carps and dietary carotenoids were found to enhance various immune defence mechanisms and also provide protection against the infection of pathogen A. hydrophila.