The efficacy of mass-marking channel catfish fingerlings by immersion in oxytetracycline

Abstract

Oxytetracycline (OTC) has been extensively used for marking a variety of fish species, but has never been successfully used to mark channel catfish Ictalurus punctatus. Channel catfish fingerlings (~ 25 mm TL) obtained from the Oklahoma Department of Wildlife Conservation at Byron Fish Hatchery were kept in Living Streams (791 to 1,018 L) equipped with recirculation units. Marking trials consisted of immersing channel catfish in one of three concentrations (250, 450, and 700 mg/L) OTC hydrochloride [HCl] for 6 hours. Samples of channel catfish were obtained from each group at 1-week and 4-week postimmersion. Lapilli otoliths and pectoral spines were removed to assess mark presence with an epi-fluorescent compound microscope. After one week, no marks were detected on pectoral spines for all treatments, mark detection on otoliths depended on concentration, but never exceeded 43% (700 mg/L). After four weeks, all otoliths and pectoral spines were determined marked for 700 mg/L OTC, 20% for fish immersed in 450 mg/L OTC, and 0% were marked after four weeks at the 250 mg/L OTC. Results show, channel catfish fingerlings can be successfully marked with immersion in OTC at 700 mg/L for at least 6 hours.