OXYTETRACYCLINE MARKING EFFICACY FOR YELLOW PERCH FINGERLINGS AND TEMPORAL ASSAYS OF TISSUE RESIDUES

Differentiating between hatchery and naturally reproduced fishes is di fficult because of the lack of appropriate marking techniques. Chemica l immersion techniques can be a practical method for mass marking juve nile fishes. The objectives of this study were to determine the concen tration of oxytetracycline (OTC) hydrochloride needed to effectively m ark age-0 yellow perch Perca flavescens, to observe the retention time of the mark, and to measure the persistence of OTC in body tissues. F ish were immersed in 309, 534, and 748 mg OTC/L for 12 h. Initial fish collections were made weekly, and monthly collections began 1 month p ostmarking for tissue and mark analyses. High-pressure liquid chromato graphy was used to quantitate OTC residues in tissues; OTC concentrati ons were undetectable (<0.05 mu g/g) in the edible tissue (muscle) at 110 d postimmersion. Aided by a Nikon Labophot fluorescence microscope , we discerned otolith marks 56 d postimmersion on 100% of the fish tr eated at 534 and 748 mg/L. Marks were still visible on 100% of the fis h treated with 534 and 748 mg/L at 8 months postimmersion.