During fish immunization studies, a massive fish kill occurred in two raceway systems holding juvenile red drum, Sciaenops ocellata. Nearly four thousand juveniles were killed in a 48-hour period. Moribund fish exhibited signs of caudal and pectoral fin paralysis prior to death due to respiratory failure. Water quality measurements were within normal limits; however, a dinoflagellate tentatively identified as Gymnodinium breve was present in high numbers. This organism, frequently associated with red tide bloams, elaborates a rapidly fatal neurotoxin.

Environmental circumstances contributing to the bloom and the implications for mariculture will be discussed.