Dietary taurine supplementation ameliorates growth performance, intestinal health, and environmental stress tolerance in summer-reared Megalobrama amblycephala.

Rising frequencies of summer heatwaves driven by climate change impose severe physiological stress on aquaculture species. This study investigated the effects of dietary taurine supplementation (0.0, 0.8%, 1.2%, and 2.0%) on the growth, intestinal health, and environmental stress tolerance of Megalobrama amblycephala. Over an 8-week trial conducted under natural temperature fluctuations (26.5‒35.3 °C), 360 fish (initial body weight: 6.47 ± 0.04 g) were randomly allocated into 12 outdoor cages (three replicates per treatment). Taurine supplementation significantly enhanced growth performance, increasing final body weight (FBW), final body length (FBL), weight gain rate (WGR), and specific growth rate (SGR) compared to the control (P < 0.001), while survival rate was unaffected (P = 0.627). Polynomial regression identified 1.460% dietary taurine as the optimal level for maximizing SGR. Whole-body composition analysis revealed that taurine elevated crude protein and reduced ash contents (P < 0.05), with no significant difference in moisture or crude lipid (P > 0.05). Furthermore, taurine improved the muscle amino acid profile, significantly raising the levels of both essential and non-essential amino acids among the 17 amino acids detected (P < 0.05). Taurine supplementation enhanced systemic antioxidant capacity by increasing total antioxidant capacity (T-AOC) and the activities of the key serum antioxidant enzymes (superoxide dismutase [SOD] and catalase [CAT]), reducing malondialdehyde (MDA) and reactive oxygen species (ROS) levels, and activating the nuclear factor erythroid 2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap-1)/heme oxygenase-1 (HO-1) pathway (P < 0.05). It also exerted anti-inflammatory effects via suppressing the nuclear factor kappa B (NF-κB) signaling pathway, reducing pro-inflammatory cytokines (il-1β, tnf-α, and il-8) and increasing anti-inflammatory mediators (tgf-β and il-10) (P < 0.05). Intestinal health was improved, as evidenced by increased villus height and muscularis thickness, higher digestive enzyme activities (amylase, lipase, and trypsin), and upregulated mucin-related gene expression (P < 0.05). Finally, taurine supplementation improved the tolerance of M. amblycephala to environmental stress. Although 1.460% taurine maximized SGR, a lower supplementation level of 0.8% provided the best overall performance when considering feed conversion ratio (FCR) and stress tolerance. Therefore, a dietary taurine supplementation of 0.8% is recommended for optimal overall performance, effectively promoting growth, reducing FCR, strengthening antioxidant and anti-inflammatory defenses, supporting intestinal barrier function, and improving climate stress tolerance in M. amblycephala. These findings support the potential practical use of taurine as an ecologically sustainable feed additive that concurrently addresses production performance and climate adaptation in M. amblycephala aquaculture.