Possible toxic mechanism of a red tide dinoflagellate, Cochlodinium polykrikoides on fish and shellfish
2009
Yamasaki, Y.(Nagasaki Univ. (Japan). Faculty of Fisheries) | Oda, T.
To elucidate the involvement of reactive oxygen species (ROS) in the ichthyotoxic mechanism of the harmful dinofiagellate Cochlodinium polykrikoides, a bioassay using damselfish (Chromis caerulea) was performed. As a result, our strain of C. polykrikoides was highly toxic to damselfish, and all individuals (n=5) died within 90 min in an intact cell suspension of C. polykrikoides, whereas the ruptured cells prepared from the same culture did not affect fish mortality. In addition, no significant reduction in the toxicity of C. polykrikoides to the damselfish was observed despite the presence of catalase, superoxide dismutase (SOD), or even both enzymes together. Furthermore, in order to clarify whether or not 5 strains of C. polykrikoides isolated at different localities in Japan generate ROS, L012-dependent chemiluminescence assays and PHPA fluorescence assays were carried out for detection of O2sup(-) and H2O2, respectively. The chemiluminescence responses and H2O2 levels in all these strains of C. polykrikoides were almost the same as the back ground levels observed in the medium alone, while obviously higher levels of chemiluminescence response and H2O2 were detected in the harmful raphidophyte Chattonella marina under the same experimental conditions. On the other hand, the aqueous extract prepared from C. polykrikoides cells showed toxic effects on the HeLa cells, but the extract of C. marina cells had no significant toxic effect. Therefore, our results suggest that certain toxic substances rather than ROS might be mainly involved in the ichthyotoxic mechanism of C. polykrikoides.
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