Withdrawal period and elimination half-life of enrofloxacin, with assessment of its impact on bioresponses of Oreochromis niloticus according to integrated biomarker response.

In intensive aquaculture, outbreaks of infectious diseases are increasing, which demand improved disease management. This study assessed the effects of dietary enrofloxacin (ENF) on Oreochromis niloticus at the recommended dose (10 mg) and overdose (30 mg/kg/day) for 5 days by using integrated biomarker response. The ENF-fed fish were observed for mortality, residue deposition, oxidative stress, plasma biochemistry, and histopathological anomalies. The withdrawal period and elimination half-life of ENF were estimated. The dosing groups experienced 0.67%-2.67% mortalities. An increase in glucose, transaminases, alkaline phosphatase, and creatinine, alongside a decrease in calcium and chloride, indicated altered physiology. The liver and kidney tissues exhibited signs of oxidative stress, as indicated by alterations in malondialdehyde, ferric-reducing antioxidant power, total nitric oxide, glutathione S-transferase, and catalase levels. Maximum residual accumulation of ENF and its metabolite ciprofloxacin was in the liver, followed by muscle + skin, kidney, and plasma. Residues of ENF and ciprofloxacin persisted in the muscle + skin and kidney at Day 42 postdosing. The projected withdrawal period at a 95% confidence limit was 22 days for the recommended dose group. The elimination half-life followed the kidney > muscle + skin > liver > plasma trend. The integrated biomarker response scores of the liver were comparatively higher than those of the kidney, indicating that the liver tissues are more prone to oxidative damage. The liver and kidney histopathology revealed dose-dependent damage, which partially recovered after ENF withdrawal. While the recommended dose induced reversible effects, the findings emphasized the need for stringent regulation and adherence to withdrawal to mitigate potential risks to fish and consumers.