The aim of the present study was to investigate the influence of dietary supplementation with Bacillus subtilis C-3102 on the productive, intestinal histomorphometry, haemato-immunological aspects, as well as evaluated the resistance of juvenile Pseudoplatystoma sp. after challenge with Aeromonas hydrophila. Inclusion levels of the commercial probiotic were set at 0 (control), 1, 2, 3 and 4% of CALSPORIN® kg feed−1 with six replicates. Blood samples were collected on day 0, 10 and 20 for hematological analysis, and on the 20th day, samples were collected for intestinal histomorphometry, zootechnical and survival analyses. The results showed that probiotic supplementation with B. subtilis significantly improved intestinal morphology in fish from groups 1% and 2% and phagocytic activity in all supplemented groups, regardless of the applied dose. In addition, on the 20th day, improvements in non-specific immunity were observed, such as an increase in the number of monocytes (groups 2, 3 and 4%), eosinophils (group 3%), leukocytes (1%) and lymphocytes (group 4%) of the fish that received the supplemented feed. It was also possible to verify that the probiotic caused significant changes in the haemogram between the sampling periods on 0, 10th and 20th day, showing activation of specialized cells of the fish’s non-specific defense mechanism. At the end of the experimental period, supplementation of B. subtilis improved the productive indexes and survival of Pseudoplatystoma sp. after bacterial challenge.
