Effects of dietary β‐(1,3)(1,6)‐D‐glucan supplementation on growth performance, intestinal morphology and haemato‐immunological profile of mirror carp (Cyprinus carpio L.)

In recent years, aquaculture research has focused on probiotics, prebiotics, and β‐glucans, in order to improve health status and growth performance. Information regarding the effects of β‐glucan on growth performance and intestinal immunity of mirror carp (Cyprinus carpio L.) is scarce. An experiment was therefore conducted to investigate the effects of a yeast β‐glucan preparation (MacroGard®) on growth performance, intestinal morphology and haemato‐immunological indices of mirror carp. Carp (initial weight 11.1 ± 0.0 g) were fed highly purified diets supplemented with 0% (control), 0.1%, 1% or 2% MacroGard®for 8 weeks. Fish fed diets containing 1% and 2% MacroGard®showed significant improvements in weight gain, specific growth rate and feed conversion ratio compared to fish fed both the control and the 0.1% MacroGard®containing diet. Histological appraisal of the intestine showed a significantly higher infiltration of leucocytes into the epithelial layer of fish fed diets supplemented with 1% and 2% MacroGard®in the anterior intestine compared to fish fed the control and 0.1% MacroGard®diet. 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. At the end of the experiment, the haematological status of the fish was examined. Compared to control fed fish, the haematocrit value was significantly elevated in fish fed the 2% MacroGard®diet. Furthermore, the blood monocyte fraction was significantly higher in fish fed the 1% and 2% MacroGard®diets. No significant changes were observed in the other blood parameters assessed. The present study shows that high dietary β‐glucan inclusion increases growth performance without detrimental effects on the health indicators assessed. Increased intraepithelial leucocytes in the anterior intestine may indicate a localized immune response; no detrimental effects on intestinal morphology were observed.