Intermittent Administration Alleviates Enrofloxacin-Induced Hepatotoxicity in Zebrafish via Adaptive Lipid Remodeling and p38 MAPK Signaling

Simple SummaryHow does antibiotic administration affect the health of farmed fish? In this study, zebrafish were exposed to enrofloxacin—a common aquaculture antibiotic—to evaluate physiological, histological, and metabolic changes in the liver using either a continuous or an intermittent regimen. We found that continuous exposure caused severe liver damage and biological stress. However, giving the fish a short break (intermittent exposure) dramatically protected their livers. This break allowed the fish to adapt and heal, preventing cellular damage despite receiving the same total amount of medication. These findings suggest that adopting “pulsed” dosing could significantly improve animal welfare and promote sustainable fish farming.Enrofloxacin (ENR) has been widely used in global aquaculture production, yet its hepatotoxic impacts under different operational administration modes remain poorly understood. Current environmental risk assessments and therapeutic guidelines generally assume that cumulative exposure dose dictates biological outcomes, largely ignoring the temporal patterns of drug administration. In the present study, we systematically compared the hepatotoxic, metabolic, and molecular effects of two matched-duration ENR administration regimens, continuous versus intermittent, on adult zebrafish (Danio rerio) at environmentally realistic concentrations (0.4, 4, and 40 μg/L). Biochemical, histological, and lipidomic analyses revealed fundamentally divergent toxicological trajectories between the two regimens. While both regimens induced significant basal triglyceride and cholesterol depletion, continuous exposure drove progressive hepatocellular damage, characterized by elevated transaminase activities, unconstrained glycogen accumulation, and the eventual collapse of antioxidant defenses, culminating in severe lipid peroxidation. Mechanistically, continuous exposure triggered sustained pathological activation of the p38 MAPK signaling cascade and broad upregulation of de novo phosphatidylcholine (PC) and phosphatidylethanolamine (PE) biosynthesis. In contrast, intermittent exposure provided a critical physiological buffering window, whereby the depuration phase enabled a sustained, adaptive antioxidant response that successfully suppressed lipid peroxidation, significantly alleviated structural liver injury, and raised the activation threshold for the p38 stress response. Furthermore, lipidomic and transcriptional profiling demonstrated that intermittent exposure uniquely induced compensatory lipid remodeling, characterized by adaptive ceramide signaling and a metabolic shift. Taken together, these findings demonstrate that the temporal pattern of exposure critically dictates ENR hepatotoxicity, highlighting the need to perform discriminative risk assessment and providing a mechanistic basis for optimizing antibiotic stewardship in aquaculture.