Effect of water temperature on the depletion of enrofloxacin and its metabolite ciprofloxacin in largemouth bass (Micropterus salmoides) tissue following repeated oral administrations

Enrofloxacin (ENR) is a veterinary antibiotic commonly used in aquaculture in some regions. However, currently established withdrawal periods do not adequately consider the varying residue depletion characteristics of ENR across different cultured species and under different temperature conditions. This study investigated temperature-dependent depletion of ENR and its metabolite ciprofloxacin (CIP) in largemouth bass at 17 °C, 22 °C, and 27 °C. Fish received oral ENR (20 mg/kg·bw) for five consecutive days, with tissue samples collected from 1 to 48 days post-administration and analyzed by HPLC-MS/MS. Results demonstrated significant temperature-dependent elimination kinetics, with higher temperatures accelerating residue depletion in all tissues. At 17 °C, ENR half-lives ranged from 2.72 days (liver) to 4.78 days (plasma), while at 27 °C, these decreased to 2.27 days and 4.30 days, respectively. The metabolite CIP exhibited faster overall depletion than the parent compound, with greater temperature sensitivity particularly in plasma and liver tissues. Tissue-specific depletion patterns revealed liver as a site of rapid clearance, followed by skin-on muscle, while kidney and gill tissues demonstrated slower depletion rates. Temperature significantly influenced withdrawal periods, with calculated withdrawal times for ENR and CIP in skin-on muscle decreasing from 29.57 days at 17 °C to 23.90 days at 27 °C. This study highlights the critical importance of incorporating temperature considerations into ENR withdrawal period determination, as current fixed withdrawal recommendations may be inadequate for ensuring food safety across varying environmental conditions.