ABSTRACT: Heterosigma carterae (formerly Heterosigma akashiwo) is a flagellated marine phytoplankter which can be toxic to many finfish, including salmonids. We have determined that, when toxic to juvenile rainbow trout Oncorhynchus mykiss, H. carterae produces high concentrations of superoxide and hydroxyl radicals as well as hydrogen peroxide. If superoxide dismutase (dismutates superoxide radical to hydrogen peroxide) and/or catalase (catalyzes the formation of water from hydrogen peroxide) are added to a toxic culture of H. carterae, it becomes markedly less toxic to juvenile rainbow trout. We propose that the toxicity of H. carterae to the salmonid O. mykiss is due to the formation of toxic concentrations of superoxide and hydroxyl radicals and hydrogen peroxide.

KEY WORDS: Heterosigma carterae . Toxic phytoplankter . Salmon . Superoxide radicals . Hydroxyl radicals . Hydrogen peroxide . Superoxide dismutase . Catalase

Published in DAO Vol. 23, No. 2 (1995) on October 26
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1995