Accumulation–Excretion Characteristics of Enrofloxacin in Farmed Largemouth Bass (Micropterus salmoides)

Enrofloxacin (ENR) is an antibiotic that is widely used in aquaculture, but residual ENR persistence in popular farmed fish such as largemouth bass (Micropterus salmoides) poses significant risks to food safety and the environment. We investigated the accumulation–excretion characteristics and environmental fate of ENR in largemouth bass fed diets containing 20 or 100 mg/kg body weight for 5 consecutive days. Our results reveal differences in ENR accumulation between the two dosage groups, with tissue-specific distribution patterns. Pharmacokinetic analysis revealed a disproportionately high increase in tissue AUC (area under the concentration–time curve) values (9.4- to 13.7-fold) relative to the fivefold dose increase from the lower to the higher dosage. Skin tissue exhibited the highest and most persistent residues, with peak concentrations 12.5-fold higher in the high-dose group, exceeding the maximum residue limit for up to 28 days. The withdrawal time calculated for skin in the high-dose group was 930 degree-days. The dose of 20 mg/kg suppressed overall growth and triggered oxidative stress and time-dependent histopathological damage. Our results underscore the necessity of mandating stricter residue surveillance in intensive aquaculture systems and highlight a need for further investigations into the mechanisms underlying dose-dependent nonlinear ENR excretion and their long-term ecological consequences.