Effects of Algal-Derived Β-Glucan on the Growth Performance, Intestinal Health And Aeromonas Veronii Resistance of Ricefield Eel (Monopterus Albus)

Abstract

Ricefield eel is an important economic fish in China. However, large-scale intensive breeding has increased the incidence of diseases in eels. In this study, we conducted an 8-weeks feeding trial to investigate the effects of β-glucan on the growth performance, intestinal health, and Aeromonas veronii resistance of Monopterus albus (M. albus). Three hundred healthy fish (average weight: 12.38 ±0.50 g) were randomly divided into five groups: A1 (basal diet) was considered the control group, whereas A2, A3, A4, and A5 were the experimental groups. The fish in the experimental groups were fed a basal diet supplemented with 250, 500, 1000, and 2000 mg/kg β-glucan, respectively. The addition of 0.025%–0.2% β-glucan significantly improved eel growth performance, with the growth performance of 0.1% β-glucan being the most significant. Furthermore, 0.025%–0.2% β-glucan could significantly enhance the antioxidant properties of the eel intestinal tract, and the addition of 0.1% β-glucan significantly improved trypsin, amylase, and lipase activities in the intestine. β-Glucan addition also altered the intestinal tissue structure of the eel, with the addition of 0.1% β-glucan exerting the most significant effect on eel intestinal tissues. At β-glucan concentrations of 0.1% and 0.2%, the richness and diversity of intestinal microorganisms and the relative abundance of Proteobacteria increased; however, the relative abundance of Firmicutes significantly decreased. Moreover, the addition of 0.05%–0.2% β-glucan significantly improved the relative survival rate of Aeromonas veronii-infected eels and significantly decreased the bacterial load of the liver, spleen, and kidney. Compared with eel without β-glucan addition, those with 0.2% β-glucan added had decreased intestinal structure damage and fewer dead cells in the spleen. In summary, the addition of 0.1%–0.2% β-glucan can promote eel growth, improve intestinal digestion and antioxidant capacity, regulate intestinal flora, and enhance intestinal physical function and anti-infection ability.

Keywords: β-Glucan, Monopterus albus, Growth, Intestinal flora, Aeromonas verinii