Effects of Algal‐Derived <i>β</i> ‐Glucan on the Growth Performance, Intestinal Health, and <i>Aeromonas veronii</i> Resistance of Ricefield Eel ( <i>Monopterus albus</i> )

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‐week 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 (initial body 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 resulted in a notable enhancement of eel growth performance, with the most significant improvement observed in eels supplemented with 0.1% β ‐glucan ( p &lt; 0.05). Furthermore, 0.025%–0.2% β ‐glucan could significantly enhance the antioxidant properties of the eel intestinal tract ( p &lt; 0.05), and the addition of 0.1% β ‐glucan significantly improved trypsin (TPS), amylase (AMS), and lipase (LPS) activities in the intestine ( p &lt; 0.05). In terms of intestinal histology, the A3, A4, and A5 groups exhibited significantly greater villus height compared to the control group ( p &lt; 0.05). Concentrations of β ‐glucan at 0.1% and 0.2% enhanced the composition of the intestinal flora; specifically, the relative abundance of Proteobacteria increased, while the relative abundance of Firmicutes decreased. Moreover, the addition of 0.05%–0.2% β ‐glucan significantly improved the relative survival rate (SR) of A. veronii ‐infected eels and significantly decreased the bacterial load of the liver, spleen, and kidney ( p &lt; 0.05). In comparison to eels that did not receive β ‐glucan supplementation, eels supplemented with 0.2% β ‐glucan exhibited decreased intestinal structural damage. 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.