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Aquaculture is a key component of the animal food industry, but intensive farming conditions increase the incidence of infectious diseases. Oxytetracycline (OTC) plays a major role for infectious diseases in fishes. Its MRLs include their 4-epimers, so in this trial, the depletion of residues of OTC and 4-epioxytetracycline in muscle and liver have been evaluated in gilthead sea bream (Sparus aurata) after oral administration. Hepatotoxicity has been investigated with histopathological effects on target tissues. A validated DAD-HPLC with SPE extraction has been applied. Residual levels in muscle and liver depleted with a similar kel, but mean retention time and t½ß resulted longer in muscle than in liver because of different vascularization. The OTC concentrations were below the LMR at 48 h after dosing. No analytical peaks ascribable to 4-epi-OTC or other derivatives were detected, while histopathology of liver showed degenerated parenchymal hepatocytes, nuclear pyknosis, focal necrosis and inflammatory leucocytes infiltration. It can be concluded that the assessment of pharmacokinetic and residual depletion of antibiotics result fundamental to determine the most suitable therapeutic regime and to minimize the toxic effects in fish species.