Use of Oxytetracycline to Mark Larval Red Drum: Survival and Mark Persistence

The objectives of this research were to optimize techniques for the mass marking of larval red drum Sciaenops ocellatus with oxytetracycline (OTC) by testing, effects of salinity (i.e., total dissolved solids [TDS], either as artificial sea salt [AS] or laboratory-grade NaCl) and immersion duration on fish survival and mark retention. Survival of larvae immersed for 24 It was greater than 83% for all combinations of salinity (15-30 g of TDS/L of water) and OTC concentration (0-500 mg of OTC/L of water). Treatments with the lowest Ca2+ and Mg2+ concentrations ([Ca2+] and [Mg2+]: i.e., highest NaCl in Substitution of AS). highest OTC concentrations, and longest exposure times yielded the poorest survival (mean +/- SD = 63.3 +/- 5.8%). Conversely, mark quality (on it scale of 1-5, where 1 = best and 5 = worst) was greatest (1.4 +/- 0.4) in treatments With the lowest [Ca2+] and [Mg2+]. Larval survival (>93%) and mark quality (2.3 +/- 0.1) were acceptable under a combination of 500-mg/L OTC, 30-g/L TDS (80% of normal [Ca2+] and [Mg2+]). and 24h exposure duration. Marks were evaluated for 20 months but could be reliably detected for only 3 months. The marking technique developed in this research may be useful in studies that require immersion marking of marine fish larvae and reliable detection for 3 months.