Disease resistance of pacu Piaractus mesopotamicus (Holmberg, 1887) fed with β-glucan

Effects of beta-glucan on innate immune responses and survival were studied in pacu experimentally infected with Aeromonas hydrophila. Fish fed diets containing 0, 0.1% and 1% beta-glucan were injected with A. hydrophila. beta-glucan enhanced fish survival in both treated groups (26.7% and 21.2% of the control, respectively). Leukocyte respiratory burst and alternative complement pathway activities were elevated after bacterial challenge regardless the beta-glucan concentration. Lysozyme activity was higher after infection and showed a gradual increase as beta-glucan concentration increased. A significant elevation in WBC count was observed either after bacterial challenge or by influence of beta-glucan separately. The same response was observed in the number of thrombocytes, lymphocytes, eosinophils, LG-PAS positive cell and monocytes. It can be concluded that feeding pacu with beta-glucan can increase protection against A. hydrophila, due to changes in non-specific immune responses.