The effect of diet composition (plant vs fish oil-based diets) on the availability of oxytetracycline in gilthead sea bream (Sparus aurata) at two water temperatures

The effect of partial fish oil replacement (66%) by rapeseed, linseed and palm oil on the availability of oxytetracycline (OTC) was investigated in gilthead sea bream (Sparus aurata). Fish received a dosage of 75 mg OTC/kg for 5 days at 27 or 14 °C water temperature. Tissues including blood and muscle plus skin were sampled on days 1, 3 and 5 during treatment and on days 6, 8, 12 and 16 post-treatment. At the high water temperature, OTC levels were undetectable in the tested tissues at all sampling points for both diets. At the winter temperature, plasma OTC concentrations were insignificantly higher in fish given plant oil-based diets compared to fish oil diets with maximum values of 1.03 and 0.73 μg/ml respectively on day 6 for both groups. Similarly, OTC muscle plus skin levels were insignificantly lower in the fish oil compared to the plant oil group with respective values of 0.48 μg/g on day 5 and 1.21 μg/g on day 6. Overall, replacement of fish oil by plant oil sources showed no significant influence on OTC availability in gilthead sea bream at winter temperatures. The use of OTC should be discouraged at very high water temperatures in this species irrespective of the diet source probably due to inhibited absorption or very rapid elimination of OTC from circulation. Long withdrawal times were necessary in gilthead sea bream fed with both plant oil (312 h) and fish oil (239 h) to ensure consumer safety at winter temperatures.