Effects of geniposide as immunostimulant on the innate immune response and disease resistance in crucian carp

Chinese herbal medicines, as the natural and innocuous compounds, have been used commonly as immunostimulants to increase growth performance, immune response and disease resistance in fish. This study aimed to investigate the effects of dietary geniposide on the immune response and disease resistance in crucian carp. The fish were fed with three different levels of geniposide-supplemented diets, including 1 mg/kg (low level group, LLG), 10 mg/kg (medium level group, MLG), 100 mg/kg (high level group, HLG) geniposide, respectively. Innate immune response, immune-related genes expression, and disease resistance against Aeromonas hydrophila infection were detected to evaluate the immunostimulant effect of dietary geniposide. The results showed that compared with control group, crucian carp fed with different levels of geniposide showed significant (p < .05) improvement serum lysozyme activity, SOD activity, complement C3 and catalase activity (CAT). Dietary geniposide increased nine immune-related genes expression in spleen and kidney with different degree. In addition, the cumulative survival percent of fish in treatment groups were significant higher than control group (10%) in challenge experiment with A. hydrophila, the relative percent survivals were 22.2%, 48.1%, and 70.4% in LLG, MLG and HLG groups, respectively. Taken together, these results suggested that geniposide used as immunostimulant was capable of improving the immune response and disease resistance against A. hydrophila infection. The supplemental level of geniposide against A. hydrophila infection in crucian carp was estimated to be about 100 mg/kg diet.