Effect of dietary β-glucan supplementation on growth, intestinal functionality and disease progression in selected cyprinids (Cyprinus carpio and Danio rerio)

Three experiments were conducted to investigate the effects of dietary supplementation of a ß-(1,3)(1,6)-D-glucan derived from the yeast Saccharomyces cerevisiae, on growth performance parameters and intestinal functionality in mirror carp (Cyprinus carpio L.) and on progression of a chronic, pre-existing mycobacteriosis in zebrafish (Danio rerio). The 1 experiment revealed that mirror carp fed diets containing 1% and 2% ß-glucan showed significant improvements in growth performance compared to fish fed both the control and the 0.1% ß-glucan containing diet. Equally, fish fed diets supplemented with 1% and 2% ß-glucan displayed significantly higher infiltration of leukocytes into the epithelial layer of in the anterior intestine. This effect was not observed in the posterior intestine. There were no significant differences in the intestinal absorptive surface area and number of goblet cells in either intestinal region. Compared to control fed fish, the haematocrit value was significantly elevated in fish fed the 2% ß-glucan diet. The blood monocyte fraction was significantly higher in fish fed the 1% and 2% ß-glucan diets. No significant changes were observed in the other blood parameters assessed. In the 2 experiment, culture-dependent microbiology unveiled that aerobic heterotrophic bacterial levels in mirror carp intestinal microbiota were unaffected by dietary β-glucan after two and four weeks. No effects were observed on the allochthonous lactic acid bacteria (LAB) populations at either time point, however, reduced autochthonous LAB populations were observed at week four. PCR-DGGE confirmed these findings through a reduction of the abundance of autochthonous LAB operational taxonomical units (OTUs) in β-glucan fed fish compared to the control fed