OXYGEN-RADICAL-MEDIATED EFFECTS OF THE TOXIC PHYTOPLANKTER HETEROSIGMA-CARTERAE ON JUVENILE RAINBOW-TROUT ONCORHYNCHUS-MYKISS

Heterosigma carterae (formerly Heterosigma akashiwo) is a flagellated marine phytoplankter which can be toxic to many finfish, including sal monids. We have determined that, when toxic to juvenile rainbow trout Oncorhynchus mykiss, H. carterae produces high concentrations of super oxide and hydroxyl radicals as well as hydrogen peroxide. If superoxid e dismutase (dismutates superoxide radical to hydrogen peroxide) and/o r catalase (catalyzes the formation of water from hydrogen peroxide) a re added to a toxic culture of H. carterae, it becomes markedly less t oxic to juvenile rainbow trout. We propose that the toxicity of H. car terae to the salmonid O. mykiss is due to the formation of toxic conce ntrations of superoxide and hydroxyl radicals and hydrogen peroxide.