Dietary fulvic acid effects on survival and expression of immune-related genes in Litopenaeus vannamei challenged with Vibrio parahaemolyticus

The effects of fulvic acid (FA) on survival and immune-related gene expression were investigated in Litopenaeus vannamei challenged with Vibrio parahaemolyticus by immersion. Shrimp were fed with different dietary FA concentrations (1, 2, 4 and 6g/kg feed) for 20days (first bioassay) or 8days (second bioassay, 2g/kg feed of FA added every 2days) and then challenged with V.parahaemolyticus. In a third bioassay, the expression of three immune-related genes (translationally controlled tumour protein [TCTP], superoxide dismutase [SOD] and heat-shock protein 70 [HSP70]) in haemocytes or hepatopancreas of experimental shrimp was measured by real-time quantitative PCR at 0, 6, 12, 24, 48, 72 and 96hr after FA (2g/kg feed) administration. Fulvic acid increased survival at a concentration of 2g/kg feed supplied every two days. Interestingly, TCTP gene expression was upregulated, whereas gene expression of SOD and HSP70 was downregulated. In conclusion, dietary fulvic acid improves survival in white shrimp challenged with V.parahaemolyticus and modulates the immune response. Therefore, FA merits further evaluation as prophylactic treatment in commercial shrimp farms.