Application of a solid-phase fluorescence immunoassay to determine oxytetracycline and tetracycline residues in tissue of olive flounder (Paralichthys olivaceus)

Parallux, a solid-phase fluorescence immunoassay (SPFIA) developed for antibotics residue detection in milk, was applied for analysis of fish tissue. The recommended therapeutic doses of oxytetracycline (OTC, 100 g/ton water, withdrawal period 30 days) and tetracycline (TC, 150 g/ton water, withdrawal period 30 days) were treated to a group of 35 olive flounders (Paralichthys olivaceus) using dipping administration. Muscle was sampled before and after drug treatment 1st, 2nd, 3rd, 5th, 7th, and 14th day. The concentration of oxytetracycline in muscle, determined by SPFIA, was compared with that of internal standard (100 ppb as oxytetracycline). The S/C ratio of sample inhibition value to cutoff inhibition value was employed as an index to determine the muscle residue in olive flounder. To investigate the recovery rate, and standard solutions were added to muscle samples to give final concentrations in muscle of 0.1 and 0.5 microg/ml. The recovery rates of all spiked samples were >89% of the spiked value. OTC and TC were detected in muscle of fishes treated until the 3rd day of withdrawal period. The present study showed that the SPFIA can be easily adopted in predicting tissue residues for OTC and TC in farmed fishes.