Sections of sagittal otoliths and dorsal fin rays from summer flounderParalichthys dentatuswere examined for fluorescent bands after injection with calcein and oxytetracycline at dosages of 25 mg/kg and 50 mg/kg of body weight. Fish were held alive 36 to 194 d after injection. Differences in holding times were due to mortalities attributed to a toxic red tide. Sagittae and dorsal fin rays were stored in darkness for 18 months prior to examination. No bands were seen on dorsal fin rays. Both fluorophors produced readable marks on sagittae when injected intramuscularly at each dosage rate; however, calcein bands were more intense than tetracycline bands. Tetracycline appeared detrimental to the health of the fish, causing reduced activity and cessation of feeding, whereas calcein did not.