| Research Abstract |
Chattonella marina, a raphidophycean flagellate, is one of the most noxious red tide phytoplankton and is highly toxic to fish, especially to yellowtail Seriola quinqueradiata. Although the precise mechanism of the toxic action or Chattonella sp.remains unclear, it has been demonstrated that a decrease in oxygen partial pressure or arterial blood is the earliest physiological disturbance observed in fish after exposure to C.marina. Physiological and histological studies of fish exposed to C.marina also suggested that the blockade of respiratory water flow through the gill lamellae caused by excessive mucus interferes with O2 transfer, resulting in asphyxia. Recent studies have shown that Chattonella sp.generates reactive oxygen species (ROS) such as O2-, H2O2, and hydroxyl radical (OH). Furthermore, it has been reported that Heterosigma akashiwo, which is also classified in a raphidophycean, produces ROS,and showed an oxygen-radical-mediated toxic effect on rainbow trout, Oncorhynchus
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mykiss. Thus, it is likely that the production of ROS is a common feature of raphidophycean flagellates. This notion is supported by our recent findings in which other raphidophycean flagellates such as Olisthodiscus luteus and Fibrocapsa japonica produce O2-and H2O2. Since harmful effects or oxygen radicals have been well documented. ROS generated by Chattonella sp.may be responsible for gill tissue injury. Interestingly, resent results domonstrated that the generation of ROS by Chattonella is stimulated by lectins such as Con A,CBH,and WGH,suggesting that cell-surface redox enzyme may be involved in O2-production, and such enzyme is responsible for the lectin-stimulation. Furthermore, Fish mucus prepared from skin and gill of yellowtail, red sea bream, and japanese flounder stimulated C.marina and H.akashiwo to generate increased amounts or O2-in a concentration dependent manner. These results suggest that fish mucus enhances the ROS mediated toxic effects of Chattonella against fish. Less
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