Nonspecific immune response in fish fed glucan diets prior to induced transportation stress

The present research studied the effects of feeding diets containing different doses of glucan on stress prevention in rainbow trout (Oncorhynchus mykiss). Different concentrations of glucan (0, 0.1, 0.5 or 1.0%) were administered to the fish over a 4-week period, then the fish were stressed by being transported for 2h. The effect of stress on the efficiency of the immune response was studied by measuring alterations of the following parameters: number and composition of the leucocyte population, phagocytosis and respiratory burst activity. At the end of the treatment, glucan-fed trout had increased levels of phagocytosis and oxidative radical production, but the data could not be correlated with the different dietary concentrations of glucan. Respiratory burst and phagocytosis appeared significantly reduced in stressed groups. The reduction was more evident in the control group, but no differences were detected between groups fed different diets. Transportation stress increased phagocytosis activity, but for control fish and fish fed 1.0% glucan it did not reach the levels observed before stress. Feeding glucan apparently induced a slight degeneration of the epithelial cells in the stomach and gut mucosae.