Enhancement of immune response and antioxidant status of Litopenaeus vannamei juvenile in biofloc-based culture tanks manipulating high C/N ratio of feed input

Biofloc technology (BFT) is a microbial manipulation technique used recently in intensive shrimp aquaculture. The driving force of BFT culture systems is microbial biofloc that is responsible for enhancing water quality, supplementing natural food, and improving growth and health of cultured shrimp. The aim of this study was to investigate the effects of biofloc on immune response and antioxidant status of Litopenaeus vannamei juveniles reared in biofloc-based tanks through manipulating high C/N ratio of feed input. Two biofloc treatments and one control were compared: Biofloc-based tanks under zero-water exchange with two levels of C/N ratio (15:1, 20:1) by addition of carbohydrate referred to as 'CN15' and 'CN20' and clear water tanks operated with high water exchange and without addition of carbohydrate referred to as 'control'. The shrimp were cultured for 30 days. The water quality in biofloc-based tanks was maintained with the promotion and development of biofloc through sucrose addition during the experiment. At the end of the experiment, the total hemocyte count in the hemolymph and the phagocytic activity of the hemocyte of the shrimp in the two biofloc treatments were significantly higher than those of the shrimp in the control group (P < 0.05). Furthermore, the total antioxidant capacity in both the plasma and the hepatopancreas of the shrimp in the two biofloc treatments was significantly higher than those of the shrimp in the control group (P < 0.05). Increased superoxide dismutase activity in the plasma, and increased reduced/oxidized glutathione ratio in both the plasma and the hepatopancreas were found in the shrimp of the two biofloc treatments (P < 0.05). There were no significant differences in all of the above parameters between the CN15 and CN20 treatments (P > 0.05). The results indicated that promoting biofloc through carbohydrate addition in zero-water exchange systems could enhance immune cellular response and antioxidant status of cultured shrimp under the conditions of the present study.