Do immunomodulatory substances facilitate recovery from stress caused by feed changes in juvenile brown trout (Samo trutta m. fario L.)?

The aim of the study was to determine the influence of feeds with or without β-glucan-based immunomodulatory supplements (groups BF and UB or B and U, respectively; feeding period 14 and 28 days) on the welfare of brown trout. The diets tested did not influence the rearing indices. The type of feed and the feeding period were confirmed to have a significant influence on the white blood cell (WBC) count. WBC counts were lower than those in the initial sample particularly on day 14 of the experiment. Red blood cell (RBC) counts and hematocrit (HCT) were determined by feeding period, and the values of these parameters decreased the longer the tested feeds were applied. These changes were accompanied by increases in the values of mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC). Feed type determined levels of chloride ion (Cl-) and ammonia (NH3) and alkaline phosphatase (ALP) activity and feeding period affected sodium (Na+) and albumin (ALB) concentrations, while aspartate aminotransferase (AST) activity depended on both factors. Changes in leukograms were noted in all the groups, inter alia, significant increases in the share of lymphocytes, and after changing diets, decreases in the percentage of neutrophils, myeloperoxidase activity (AMPO) in phagocytes and cidal ability (CA). After day 28, AMPO and CA values increased and were significantly higher in groups BF and UB.