Dietary Supplementation with Organic Acids Improves Production Performance and Intestinal Health of Largemouth Bass

Organic acid supplementation in aquafeed plays a crucial role in enhancing fish health and performance, contributing to sustainable aquaculture practices amid growing global demand for protein sources. In a feeding trial lasting 8 weeks, 360 juvenile fish (43.5 ± 0.23 g) were randomly assigned to four groups (three replicates per group; 30 fish per replicate), following one of four dietary regimens: the control (CON), or the control diet supplemented with 0.3% citric acid, 0.3% fumaric acid, or 0.3% malic acid. The supplementation of diets with the three organic acids significantly promoted weight gain (WG) and specific growth rate (SGR). Additionally, a significant increase in the activities of serum antioxidant enzymes (SOD, CAT, AKP) was recorded, with concomitant decreases observed in hepatic parameters (TG, GLU, ALT, AST) and the serum lipid peroxidation product MDA. Similarly, the organic acids supplementation also enhanced the hepatic antioxidant capacity (CAT, T-AOC, GSH-PX) and their gene expression levels, and decreased hepatic lipid and glycogen levels. Additionally, dietary organic acid supplementation significantly enhanced the activities of both digestive and antioxidant enzymes in the intestine. Furthermore, it improved intestinal morphology, as evidenced by increases in villus height, villus width, and muscular thickness. Moreover, supplementation with organic acids improved intestinal permeability, mediated through the suppression of serum DAO activity and LPS levels, accompanied by upregulated intestinal expression of junction complex components (Claudin-1, ZO-1, Occludin-1) and downregulated pro-inflammatory mediators (tnf-α, il-1β). The 16S rRNA sequencing demonstrated that CA induced a significant shift in the intestinal microbiota composition, marked by an elevated relative abundance of Firmicutes (including Streptococcus) and Acinetobacter, along with a decreased abundance of Aeromonas. These findings demonstrate that organic acids may enhance fish growth performance and intestinal health through their modulating effects on gut microbiota, intestinal development, immune responses, and antioxidant capacity. Notably, the dietary CA supplementation exhibited the most pronounced efficacy.