Effects of fermented sweet potato residue on growth performance, immune organ morphology, antioxidant capacity and nonspecific immunity in common carp (Cyprinus carpio)

The aim of this study was to investigate the effects of fermented sweet potato residue (FSP) on growth performance, immune organ morphology, antioxidant capacity and nonspecific immunity in common carp. One hundred and twenty healthy and disease-free common carp with an initial body weight of (408.36±26.12) g were randomly divided into four groups, FSP0, FSP10, FSP20 and FSP30, and their base diet was supplemented with 0, 10%, 20% and 30% FSP, respectively.There were with 10 common carp in each tank, and the experiment was replicated three times. The results showed that the weight gain rate and specific growth rate of the FSP10 and FSP20 groups were significantly greater (p<0.05) than those of the FSP0 group. The structure of the headkidney and spleen were normal in all test groups, there were no inflammatory changes. However, the length of the intestinal villi and the thickness of the intrinsic muscularis layer were significantly increased (p<0.05) and the depth of the mucosal crypts significantly decreased (p<0.05). With the addition of FSP; the activity of GSH-Px in the spleen of the common carp in the FSP20 group significantly increased; TNF-α content in the kidneys of common carp in the FSP10 group significantly increased (p<0.05); and IL-1β content in the kidneys of common carp in the FSP30 group significantly increased (p<0. 05), Moreover, IFN-γ content in the spleens of common carp in the FSP20 and FSP30 groups was significantly lower (p<0.05). This study showed that FSP did not affect the normal morphology or structure of the headkidney, spleen or intestine of the common carp, and to a certain extent, it could improve the growth performance of common carp; and effectively induce a nonspecific immune response in common carp. The addition of 20% FSP was more appropriate.