Determination of residue in muscle and skin of sea bass (Dicentrarchus labrax L., 1758) after oxytetracycline treatment

The research were carried out in order to determine residue depletion of oxytetracycline HCl in the muscle and skin of Listonella anguillarum infected sea bass (Dicentrarchus labrax) which were held in floating net cage placed in sea water. They were fed with commercial pelleted diet at a rate of 1% biomass. Oxytetracycline HCl were given to fish one time in a day 75 mg/kg living weight for 10 days in the fed. It was attached to the pellet with mixing starch. Muscle and skin without scales and bones were sampled from fish netted at different intervals after last treatment (1st, 2nd, 3rd, 4th, 5th, 9th, 10th, 14th, 15th, 19th, 20th, 24th, 25th, 29th, 30th, 37th and 44th day). Oxytetracycline HCl were extracted from muscle and skin tissues by using 0.1 M KH sub(2)PO sub(4) or 2% 0.1 M HCl containing methanol and determined in bacteriolological method. Bacillus cereus var. mycoides (ATCC-11778) were used as test organism and seeded on to Antibiotic Medium No: 2 (pH 5.95 plus or minus 0.05). A great variation were recorded in tissue residue of oxytetracycline HCl depending variation of feed intake. Oxytetracycline concentrations in muscle of naturally L. angullarium infected sea bass were declined under maximum residue limit (MRL) 20 days (0.034 mu g/g) after treatment ceased. This is equal to 456 degree/days. However, skin oxytetracycline HCl concentration was declined below MRL (0.046 mu g/g), 30 days after treatment ceased. This is equal to 684 degree/days.