Effects of dietary soy isoflavones on growth, antioxidant status, immune response and resistance of juvenile grass carp (Ctenopharyngodon idella) to Aeromonas hydrophila challenge

The current study was conducted to evaluate the effect of dietary soy isoflavones (SI) on growth performance, antioxidant status, immune response and resistance to Aeromonas hydrophila in juvenile grass carp (Ctenopharyngodon idella). Six diets were formulated to contain 0 (control), 10, 50, 100, 500 or 1,000 mg SI per kg feed. Each diet was randomly allotted to triplicate net cages, and each net cage was stocked with 30 fish. The fish were fed one of the experimental diets to satiation twice per day for 60 days. The results showed that the WGR and DGC of the 500 mg/kg SI-supplemented group were significantly higher than those of the non-SI-supplemented group (p < .05). Serum LZM and IgM activities in the SI-supplemented groups were improved compared to the control group. SOD and GSH-Px levels of fish fed the diet containing 500 mg/kg SI were significantly enhanced compared to those of fish fed the control diet (p < .05). Additionally, serum CAT, GSH-Px and AKP activities in 50, 100 and 500 mg/kg SI-supplemented groups were significantly higher than that in the control group (p < .05). The expression of most immune-related genes (including IFN-gamma 2, TNF-alpha, M-CSF2, IL-6, IL-12p40 and IL-4) was significantly affected by dietary supplementation of SI. The group fed with 500 mg/kg SI had the highest 7-day cumulative survival rate after challenge test (p < .05). The current results revealed that dietary inclusion of SI could improve the immune response and resistance against A. hydrophila and the supplementation level is suggested to be 500 mg/kg diet.