Zinc supplementation in practical diets for pond-raised hybrid snakehead (Channa maculate ♀ x Channa argus ♂) fingerlings: Effects on performance, mineral retention and health

Zinc (Zn) is an essential micromineral for fishes and is closely related to many biochemical processes. This study was designed to determine the effects of dietary Zn supplied in practical diets on the pond-raised hybrid snakehead (Channa maculate female x C. argus male). Five extruded diets were supplemented with different Zn sulfate levels (analysed Zn values: 42.33, 65.79, 82.27, 100.41, and 120.18 mg kg(-1)). A total of 900 fish (initial weight 3.33 g) were divided into three net cages per treatment and fed twice daily to apparent satiety. The results indicated that dietary Zn influenced growth parameters, antioxidant capacity and innate immunity. The moisture and crude lipid contents of the whole body were significantly affected by dietary Zn concentration (P < 0.05). The whole-body, hepatic, and vertebral Zn concentrations were not significantly affected by dietary Zn level (P > 0.05). However, copper (Cu) content in the whole body, vertebrae, and liver increased and then decreased as dietary Zn increased (P < 0.05). The content of whole body Zn was significantly positively correlated with whole body Fe, Mn (P < 0.01) and liver Cu (P < 0.05), and negatively correlated with whole-body Cu (P < 0.01). The content of liver Zn was positively correlated with liver Cu, Mn (P < 0.01), liver and whole body Fe (P < 0.05). Dietary Zn supplementation mitigated the generation of free radicals and improved the antioxidant capacity of hybrid snakehead. Plasma immune parameter activity and innate immune ability were both enhanced by appropriate dietary Zn levels. Liver Zn level was positively correlated with plasma C3 and TP (P < 0.05). Regression analysis of feed utilization, antioxidant and innate immunity parameters indicated that the optimum zinc concentration in a practical diet for fingerlings hybrid snakeheads ranged from 81.94 to 101.05 mg kg(-1).