Effect of Dietary Supplementation of Bacillus subtilis and Terribacillus saccharophillus on Innate Immune Responses of a Tropical Freshwater Fish, Labeo rohita

Abstract

Objective: Indiscriminate use of antibiotics to control fish diseases has led to the development and propagation of antibiotic resistant bacteria in aquatic ecosystems. Amongst the various alternatives proposed, enhancing immunity in fish using probiotics is the most widely accepted approach. Several earlier studies indicated the possibility of more potent effects of bacteria on fish when administered in live condition than as inactivated cells. But very few studies have explored the effect of gut bacteria on innate immune responses of fishes. Hence an attempt is made to study immunostimulatory effects of dietary supplementation of Bacillus subtilis and Terribacillus saccharophillus isolated from the gut of an edible Indian freshwater fish, Labeo rohita, in the same species.Methods: Long term administration (for 30 and 60 days) of B. subtilis or T. saccharophillus isolated from the gut wall of L. rohita were tested in the same species for their ability to improve innate immunity through measurement of the phagocytic activity, respiratory burst, myeloperoxidase activity, serum IgM levels, serum lectins, haemagglutination and haemolytic activity.Results: Dietary administration of 107 cfu/g of B.subtilis/T. saccharophillus for 30 (B 1 ) or 60 (B 2 ) days resulted in a significant increase in immune and humoral responses of L. rohita. Serum phagocytic activity, respiratory burst activity, myeloperoxidase activity, serum lectins, haemagglutination and haemolytic activity increased upon administration of B.subtilis / T. saccharophillus, except serum IgM levels which increased only in B 1 . A positive correlation was observed between the duration of supplementation of diets and the responses in both the cases. Conclusion:The results suggest that T. saccharophillus can also be used as a potent probiont similar to B.subtilis and both will have significant applications in fish feed formulations and disease prevention.