RESEARCH ARTICLE Progress in Understanding Algal Bloom- Mediated Fish Kills: The Role of Superoxide Radicals, Phycotoxins and Fatty Acids

Quantification of the role of reactive oxygen species, phycotoxins and fatty acids in fish tox-icity by harmful marine microalgae remains inconclusive. An in vitro fish gill (from rainbow troutOncorhynchus mykiss) assay was used to simultaneously assess the effect in super-oxide dismutase, catalase and lactate dehydrogenase enzymatic activities caused by seven species of ichthyotoxic microalgae (Chattonella marina, Fibrocapsa japonica, Het-erosigma akashiwo, Karenia mikimotoi, Alexandrium catenella, Karlodinium veneficum, Prymnesium parvum). Quantification of superoxide production by these algae was also per-formed. The effect of purified phycotoxins and crude extracts was compared, and the effect of fatty acids is discussed. The raphidophyte Chattonellawas the most ichthyotoxic (gill cell viability down to 35%) and also the major producer of superoxide radicals (14 pmol cell-1 hr-1) especially after cell lysis. The raphidophyte Heterosigmaand dinoflagellate Alexan-driumwere the least toxic and had low superoxide production, except when A. catenella was lysed (5.6 pmol cell-1 hr-1). Catalase showed no changes in activity in all the treatments. Superoxide dismutase (SOD) and lactate dehydrogenase exhibited significant activit