Dietary fulvic acid improves immune, digestive and antioxidant parameters in juvenile white-leg shrimp (Litopenaeus vannamei) in a super-intensive system

In the current study, the effects of dietary fulvic acid supplementation at levels of 0.5, 1 and 2% were examined in white-leg shrimp, Litopenaeus vannamei. A significant increase in the weight of the shrimp was observed in the group treated with 2% fulvic acid in comparison to the control group. This may have been associated with an increased digestive efficiency, with the food conversion ratio reducing from 2.4 to 1.9, and increased hepatopancreatic amylase, protease, and lipase enzyme activities. Enhanced activity of hemolymph superoxide dismutase was suggestive of an enhanced immune capacity, while hemolymph cell count increased by 16.4 and 13.6% in shrimp receiving diets supplemented with 1 and 2% fulvic acid, respectively. Additionally, the number of large granular cells increased by 37.3% and 40.8% relative to the control in these two groups. Furthermore, the lysozyme activity increased in shrimp receiving dietary supplementation of 1% and 2% fulvic acid by 16.7% and 24.7%, respectively. Phenol oxidase activity, which activates phagocytosis and encapsulation of invading pathogens, increased in all groups supplemented with fulvic acid, with the highest activity in the 1% fulvic acid group. Overall the present results suggest that fulvic acid is a promising feed additive for white-leg shrimp super-intensive culture.