Comparative study on the toxic factors of Chochlodinium polykrikoides and Chattonella marina

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Generation of reactive oxygen species (ROS) by Chattonella marina could be confirmed by ESR spin trapping method. Immunohistochemical analysis of gill lamellae from yellowtail exposed to C.marina using antiserum against crude glycocalyx demonstrated that there were the antigns recognaised by the antiserum on the surface of gill lamellae. As compared to C.marina, the levels of ROS detected in Cochlodinium polykrikoides were trace levels. Furthermore, no significant increase in O^2_- generation by C.polykrikoides was observed in the presence of lectins or fish mucus prepared from skin and gill of yellowtail, whereas C.marina generated increased level of O^2_- responding to these stimuli. The cell-free aqueous extract prepared from C.polykrikoides showed toxic effect on HeLa cells, but the extract of C.marina had almost no effect. Furthermore, gradual accumulation of polysaccharides in the medium was observed during the culture of C.polykrikoides, but no such change was observed in the medium of C.marina. These results suggest that ROS may play a significant role in the fish-killing activity of C.marina, whereas in the case of C.polykrikoides, certain toxic substances or polysaccharides are mainly responsible for the toxicity rather than ROS.