Integrative Pharmacokinetic and Metabolomic Analyses Reveal the Underlying Mechanisms of Metabolic Regulation and Support the Safe Use of Oxolinic Acid in Micropterus salmoides

Infections caused by <i>Aeromonas hydrophila</i> lead to significant economic losses in <i>Micropterus salmoides</i> aquaculture. Prior to the single-dose oral administration via gavage, the antibacterial efficacy of Oxolinic Acid (OXO) against the <i>Aeromonas hydrophila</i> strain NJ-35 was initially validated using in vitro assays. Subsequently, this study evaluated the pharmacokinetics, tissue residue depletion, and safety of OXO following a single oral dose (30 mg/kg) via medicated feed. The highest tissue concentration was observed in the kidney (C_max 17.99 mg/L), while the muscle, the primary edible tissue, reached 4.54 mg/L. Residues in all tissues declined significantly by 72 h, supporting a withdrawal period of 476 degree-days. Metabolomic and biochemical analyses at peak concentration times revealed OXO-induced oxidative stress. Perturbations in the kidney were primarily associated with amino acid metabolism, whereas the muscle exhibited alterations in both lipid and amino acid pathways. Corresponding changes in oxidative stress markers were also detected. These metabolic disturbances and biochemical shifts gradually resolved as OXO was eliminated. This study confirms the in vitro antibacterial efficacy of OXO, establishes a practical withdrawal period, and demonstrates its overall effectiveness and safety profile in <i>Micropterus salmoides</i> under the experimental conditions. The findings provide crucial data for the judicious use of OXO in freshwater aquaculture, highlight transient metabolic effects, and contribute to supporting sustainable farming practices.