TISSUE DISTRIBUTION AND RESIDUE DEPLETION OF OXYTETRACYCLINE IN SEA BREAM (SPARUS-AURATA) AND SEA BASS (DICENTRARCHUS-LABRAX) AFTER ORAL-ADMINISTRATION

Tissue distribution and residue depletion of oxytetracycline (OTC) fol lowing oral administration were evaluated in sea bream and sea bass un der field conditions. Fish were held in floating cages placed in sea w ater and fed a commercial medicated diet containing 7.5 g/kg of OTC on ce daily for 14 days at a rate of 1.0% (75 mg a.i./kg) biomass per day . Muscle, liver, vertebrae, and skin with scales were sampled from fis hes netted at different intervals during (2(nd), 4(th), 6(th), 10(th), and 14(th) day) and after treatment (10(th), 20(th), 30(th), 40(th), 50(th), and 60(th) day). OTC analyses were carried out by HPLC, after SPE extraction. In sea bream, a great variation in drug intake was evi dent from the inter-subject differences in OTC tissue concentrations. The highest recorded concentrations were in skin and pooled liver (7.7 0 +/- 6.71 mu g/g and 14.65 mu g/g at the 6(th) day, respectively). Ve rtebrae showed concentrations even six-fold higher than those in muscl e, and reached steady state concentrations at the 40(th) day after the end of treatment (1.73 +/- 0.92 mu g/g), lasting until the end of the study. OTC concentrations in muscle were lower than in all the other tissues throughout the entire experiment and declined under 0.1 mu g/g 20 days after treatment ceased, In sea bass a high mortality not rela ted to infectious diseases was observed and muscle samples had only tr aces or no detectable OTC levels even during medication.