Effects of <i>Lactobacillus acidophilus</i> AC on growth, intestinal flora and metabolism of juvenile large yellow croaker ( <i>Larimichthys crocea</i> )

Abstract The intensive aquaculture model has increased the incidence of disease outbreaks in fish, and the prolonged use of antibiotics and chemicals can adversely affect the health of farmed fish and the environment. Consequently, there is an urgent need to develop eco‐friendly feed additives as alternatives. The experiment was conducted with four groups: LA0 (the control), LA9 (10 9 CFU/g L. acidophilus AC), LA10 (10 10 CFU/g L. acidophilus AC) and LA11 (10 11 CFU/g L. acidophilus AC); each group had three replicates, and the trial lasted for 56 days. The results showed that compared with the LA0 group, the LA11 group exhibited a significantly lower viscerosomatic index (VSI) ( p &lt; 0.05). Moreover, the LA9 and LA10 groups displayed significantly higher muscle moisture content and lower fat content ( p &lt; 0.05). The hepatic acid phosphatase (ACP) activity in the LA9 and LA11 groups was significantly elevated ( p &lt; 0.05), and the serum lysozyme (LZM) activity in the LA10 group was significantly higher compared with that of the LA0 group ( p &lt; 0.05). The intestinal villus height in the LA9 and LA11 groups was significantly increased than that in the LA0 group ( p &lt; 0.05), as well as up‐regulated the number of goblet cells in the LA11 group ( p &lt; 0.05). Intestinal lipase activity in the LA9 group was significantly higher than that of the LA0 group ( p &lt; 0.05). Dietary supplementation with L. acidophilus AC significantly increased the relative abundance of beneficial bacteria, including Arenimonas , Methylobacterium‐Methylorubrum , OM27 clade , Roseomonas and Subdoligranulum in the intestine of the LA9 group ( p &lt; 0.05). Intestinal metabolomics analysis revealed significant reductions in the concentrations of PS (24:0/22:6 (5Z, 7Z, 10Z, 13Z, 16Z, 19Z)‐OH (4)), galabiosylceramide (d18:1/26:1 [17Z]) and PC (24:0/22:6 (4Z, 7Z, 11E, 13Z, 15E, 19Z) ‐2OH (10S, 17)) in the LA9 group ( p &lt; 0.05), while the concentration of 3b,6a‐dihydroxy‐alpha‐ionol 9‐[apiosyl‐(1‐ &gt; 6)‐glucoside] was significantly elevated ( p &lt; 0.05). Further analysis indicated that the differential metabolites were primarily associated with neomycin, kanamycin and gentamicin biosynthesis pathways. In conclusion, L. acidophilus AC can enhance the digestive and absorptive capacity and regulate the antioxidant and immune ability of large yellow croaker by regulating the intestinal microbiota and metabolism.