Influence of β‐glucan on innate immunity and resistance of Lutjanus guttatus to an experimental infection of dactylogyrid monogeneans

Summary The present study investigated the effect of β‐1,3/1,6‐glucan on growth, haematology, innate immunity and resistance against dactylogyrids on the spotted rose snapper (Lutjanus guttatus). Fish were fed during 5 weeks with commercial diet (control group) and same diet supplemented with three levels of β‐glucans (0·05%, 0·1% and 0·5%/kg feed). The results showed that at concentrations of 0·05% and 0·1%, fish growth was enhanced, and in weeks 2 and 4, an increase in cellular responses such as percentage of monocytes, neutrophils, respiratory burst activity and nitric oxide activity was observed. In diet with 0·5%β‐glucans, changes were registered at the end of the experiment. At week 2, 0·05%β‐glucans showed the best response to most of the analysed parameters. In a second trial, diet with 0·05%β‐glucans was chosen to prove its effect on the resistance of infected fish with monogeneans. The results showed that fish reduce significantly the number of dactylogyrids, and parameters such as WBC, percentage of lymphocytes, neutrophils and eosinophils were increased. In addition, WBC and percentage of thrombocytes increased in the control (+). The β‐glucans have the potential to be use in diet formulations of the spotted rose snapper and to limit the adverse effects of dactylogyrids.