Dietary microbial floc potentiates immune response, immune relevant gene expression and disease resistance in rohu, Labeo rohita (Hamilton, 1822) fingerlings

Effects of dietary administration of microbial floc on immune response, immune relevant gene expression and resistance of rohu (Labeo rohita) against Edwardsiella tarda were investigated in the present study. Microbial flocs were collected from a biofloc system, dried and ground into fine powder. Four isonitrogenous diets were prepared with the addition of graded level of floc powder at 0% (control), 4% (B4), 8% (B8) and 12% (B12) inclusion. Fingerlings of rohu (1036 +/- 0.71 g) were fed with these diets and various immune responses, immune relevant gene expression and disease resistance were measured after 4 weeks of feeding. Different immunological parameters viz. oxygen radical production and lysozyme activity showed significant enhancement in fish fed with the B4 diet. However, myeloperoxidase and alkaline phosphatase activity did not show any significant difference. Immune relevant genes viz. IL-1 beta, IFN-gamma, TNF-alpha, C3, iNOS and IL-10 showed significantly higher expression in liver and head-kidney tissues in most of the cases for the B4 and B8 diets. The B4 diet enhanced the resistance of rohu substantially against E. tarda challenge. In conclusion, the dietary supplementation of microbial floc meal had a health ameliorating effect in rohu particularly, at 4% inclusion level. The results collectively suggest the potential of applying microbial floc meal as immunostimulant in aquaculture. (C) 2016 Elsevier B.V. All rights reserved.