Leaching, palatability and digestibility of oxytetracycline and oxolinic acid included in diets fed to seabass Dicentrarchus labrax L.

The leaching of oxolinic acid (OA) and oxytetracycline (OTC) from medicated feeds, as well as the palatability and digestibility of these drugs were i nvestigated in seabass Dicentrarchus labrax L. (350 g) at 16 degrees C and 24 degrees C water temperature. Oil-coated OA and OTC on feeds were greatly affected by leaching at 16 degrees C (losses of 55.5% and 42.5% for OA and OTC respectively) and 24 degrees C (32% for OA and 47% for OTC), However, a significant reduction in drug loss resulting from leaching was evident wh en the antibiotics were mixed with the diet at 16 degrees C (5% for OA and 6.5% for OTC) and 24 degrees C (10% and 20% for OA and OTC respectively). I ncreased water temperature induced a significant effect on the leaching of both drugs when mixed with the feed, but did not affect the loss of oil-coa ted drugs. There was a significant reduction in feed consumption of fish fe d a diet with oil-coated OTC (90% and 92% at 16 degrees C and 24 degrees C respectively), whereas intake of feed containing oil-coated OA was only sli ghtly affected (10% at 16 degrees C, 12% at 24 degrees C). The depressed pa latability of feeds containing oil-coated OTC was overcome by mixing the dr ug with the diet. Both antibiotics were well digested by seabass (94% and 8 5% for OA and OTC respectively) at 24 degrees C; however, more than one-thi rd of each drug was recovered in the faeces at 16 degrees C (64% and 59% fo r OA and OTC respectively). The significance of these findings for the inte raction between fish therapy and marine environment is stressed.