Autochthonous Bacilli and Fructooligosaccharide as Functional Feed Additives Improve Growth, Feed Utilisation, Haemato-Immunological Parameters and Disease Resistance in Rohu, Labeo rohita (Hamilton)

SIMPLE SUMMARY: The application of probiotics, prebiotics and synbiotics as functional feed additives has created increasing attention towards environment-friendly aquaculture. In this study, the effects of autochthonous Bacillus spp. (probiotics) and fructooligosaccharide (FOS, prebiotic) have been evaluated, either alone or in combination (synbiotics), for an Indian major carp (rohu), Labeo rohita fingerlings. The results indicated that the combination of B. licheniformis and FOS significantly improved live weight gain, feed utilisation and protease activity in fish compared to the other groups. In general, probiotics- and synbiotics-supplemented groups exhibited improved haematology, serum biochemical profiles and immune parameters compared to the control group. After 90 days of feeding, the fish were experimentally exposed to a pathogenic bacterium, Aeromonas hydrophila. Data on the haematology, immunity and stress parameters revealed that synbiotics application boosted immunity and relieved physiological stress in fish. The highest survival among the pathogen-infected fish was recorded with the dietary application of synbiotics consisting of B. licheniformis and FOS. In addition, fish fed a combination of B. methylotrophicus and FOS in their diets also survived well. Thus, we suggest the application of synbiotics containing autochthonous bacilli and FOS to improve growth, immunity and pathogen resistance in fish. ABSTRACT: The effects of Bacillus spp. (7 Log CFU g(−1) feed) and fructooligosaccharide (FOS, 1%) as functional feed additives, either alone or in combination, were evaluated in a study on rohu, Labeo rohita fingerlings. The fish were fed different diets for 90 days, including a control diet and diets supplemented with FOS, B. licheniformis, B. methylotrophicus or synbiotic formulations of these. The results showed that the combination of B. licheniformis and FOS significantly improved weight gain, feed utilisation and protease activity compared to the other groups. Overall, the groups supplemented with probiotics and synbiotics (B. licheniformis + FOS or B. methylotrophicus + FOS) showed improvements in haematology, serum biochemistry and immune parameters compared to the control group. After 90 days of experimental feeding, the fish were challenged with pathogenic Aeromonas hydrophila, and data on haematology, immunity and stress parameters were collected. The results indicated that the application of Bacillus spp. and FOS boosted immunity and resistance to physiological stress in the fish. The highest post-challenge survival rate was observed in fish fed a diet with B. licheniformis and FOS, indicating the potential of this particular combination of functional feed additives to enhance growth, immunity and disease resistance in L. rohita.