Retention of Oxytetracycline-Induced Marks on Sagittae of Red Drum

Abstract

In a pilot-scale stocking program, juvenile red drum Sciaenops ocellatus were immersed for 4 h in a 500-mg/L active solution of oxytetracycline hydrochloride (OTC) and 15-g/L salinity water at a temperature of 26.2°C to mark the otoliths before release. A portion of the treated fish was retained to determine marking success and mark retention. Retained fish were held in outdoor tanks supplied with flow-through estuarine water from Charleston Harbor, South Carolina, and fed commercial trout diets daily. During a 4.4-year period, subsamples of treated fish were regularly sacrificed, and their sagittae were removed, sectioned, and examined under an epifluorescent microscope to validate presence of a mark. Because of interference from autofluorescence, OTC marks were not detectable on sagittae from fish sampled 56 d after immersion (N = 4). However, a mark was visible on 100% of sagittae examined from treated fish sampled on nine occasions from 73 to 1,618 d after immersion (N = 46). In a blind test, both marked and unmarked (wild) otoliths were assigned to their respective category with 100% accuracy. Thus, OTC immersion can be used to provide an accurate, long-term means of marking juvenile red drum.