Single or conjoint application of autochthonous Bacillus strains as potential probiotics: Effects on growth, feed utilization, immunity and disease resistance in Rohu, Labeo rohita (Hamilton)

The study evaluated effects of dietary administration of Bacillus spp., either single or in combination, on growth performance, immune response and disease resistance in rohu, Labeo rohita (Hamilton) fingerlings. The fish were fed for 60 days with control diet (without probiotics) or diets supplemented with 1 x 10(7) cells g(-1) of B. methylotrophicus (E1), B. amyloliquefaciens (E2), B. licheniformis (E3), B. methylotrophicus + B. amyIo1iquefaciens (E4), B. methylotrophicus + B. licheniformis (E5) and B. amyIo1iquefaciens + B. licheniformis (E6). Results indicated that combination of B. methylotrophicus and B. licheniformis (E5) produced significant (P < 0.05) improvement in specific growth rate (% d(-1)), feed conversion ratio and condition factor, when compared to the control and other experimental groups. Immune and blood parameters were examined after 30 and 60 days of feeding. Overall, probiotics supplemented groups (E1 -E6) were noticed with improved immune and hematological parameters in comparison to the control group. Serum lysozyme, alternative complements pathway, antiprotease and peroxidase activities were significantly higher in L. rohita reared on conjoint application of probiotics (E4-E6) than other experimental groups (E1 -E3, fed single probiotics) and the control group. Further, conjoint application of probiotics significantly increased phagocytic and respiratory burst activities in fish. A significant enhancement in serum IgM level was noticed in the experimental groups after 30 days of feeding, while decreased thereafter. Data on stress enzymes (glutamic oxaloacetic transaminase and glutamic pyruvic transaminase) revealed that probiotics application did not create physiological stress on the fish. Further, after exposure to Aeromonas hydrophila, the highest post-challenge survival (87.33 +/- 0.67%) was recorded in fish fed diet E5, which was followed by E6 (78.67 +/- 0.88%). Consequently, supplementation of B. methylotrophicus and B. licheniformis in equal proportions might be recommended to improve growth, immunity and disease resistance in L. rohita.