Immersion Marking of Juvenile Midas Cichlids with Oxytetracycline

Abstract

Laboratory experiments were conducted on the use of oxytetracycline hydrochloride (OTC) for marking juvenile Midas cichlids Amphilophus citrinellus. Juveniles were immersed in tris-buffered OTC solutions of 200, 400, or 600 mg/L for 4, 8, or 16 h. Marked juveniles were detected by the presence of a fluorescent mark on spines and rays when viewed under an ultraviolet light. Immersion in 600-mg/L OTC solution for 8 h produced the optimum mark intensity. No immediate mortality occurred after the marking procedure. Retention of the externally visible marks and effect of OTC treatment on long-term survival were examined by rearing both marked and unmarked juveniles for 6 weeks. Marks were visible for 2–7 weeks, depending on the size of the juveniles when marked. Marking with OTC had no effect on survival over the 6-week period. The effects of light exposure on retention and intensity of externally visible marks were examined by rearing marked fry under both dark and light conditions. Retention and intensity of externally visible marks were greater in juveniles held in the dark. The effect of OTC treatment on the vulnerability of juveniles to predation was determined by subjecting both marked and unmarked juveniles to predation by bigmouth sleepers Gobiomorus dormitor 72 h after OTC treatment. OTC marking did not affect the vulnerability of juveniles to predation. Our results indicate that this OTC marking technique would be suitable for short-term mark–recapture, growth, and alloparental care studies of Midas cichlids.