Oxygen Radical Production by a Red Tide Flagellate Chattonella and its Ichthyotoxicity

只有当死亡发生时，双氧水浓度（[H_2O_2]）在黄尾鱼暴露于查顿菌后立即增加到约1.5 μ mol/l。在鱼存活的情况下，在整个实验中没有检测到H_2O_2。在环境水中添加5 μ mol/l的[H_2O_2]对鱼的生理反应无明显影响。因此，过氧化氢本身并不是造成查顿菌致鱼死亡的原因。颊腔和眼腔样品中[H_2O_2]含量无明显差异。甘露醇是一种OH自由基清除剂，其作用延长了鱼的存活时间，提示OH自由基参与了查顿菌致鱼死亡机制。当日本比目鱼（palichthys olivaceus）暴露于查顿菌时，血Po_2迅速下降，黄尾鱼也是如此。然而，与黄尾鱼不同的是，在7小时的暴露中没有鱼死亡。这两种鱼类对查顿菌的易感性的差异被认为是由于它们对缺氧的耐受性不同。然后我们比较了黄尾鱼、红鲷鱼和比目鱼鳃中过氧化氢酶和超氧化物歧化酶（SOD）的活性。比目鱼过氧化氢酶的Vmax显著低于黄尾鱼，红鲷的活性处于中等水平。过氧化氢酶Km和超氧化物歧化酶活性在三种间无显著差异。鳃中过氧化氢酶活性的差异也可能是黄尾鱼对查顿菌敏感性较高的原因。组织学检查显示，当恰顿菌暴露初期Po_2下降时，鳃部未形成水肿。在这些鳃样品中观察到的唯一组织学变化是粘液堵塞了纤维间隙。查顿菌产生氧自由基与粘液分泌的关系有待于进一步的研究。少

Only when mortality occurred, hydrogen peroxide concentration ([H_2O_2]) increased up to ca. 1.5 mumol/l immediately after the onset of exposure of the yellowtail, Seriola quinqueradiata, to Chattonella. In cases where fish survived, H_2O_2 was not detected throughout the experiment. Fish showed no physiological perturbations in response to [H_2O_2] of 5 mumol/l added to ambient water. Thus, hydrogen peroxide per se was not responsible to fish kill by Chattonella. There was no detectable difference in [H_2O_2] between samples collected from buccal and opercular cavities. When the effect of mannitol, known as an OH radical scavenger, was tested, survival of fish was prolonged, suggesting the involvement of OH radical in fish kill mechanism by Chattonella.When the Japanese flounder, Paralichthys olivaceus, were exposed to Chattonella, blood Po_2 rapidly declined as was the case in the yellowtail. Unlike yellowtail, however, no fish was killed during 7 hr of exposure. The difference in su … More sceptibility to Chattonella between these two fish species was considered to be attributable to difference in hypoxia tolerance between them.We then compared the activities of catalase and superoxide dismutase (SOD) in the gills of the yellowtail, red sea bream, and flounder. The Vmax of catalase was significantly lower in the flounder than in the yellowtail, red sea bream showing an intermediate activity. The Km of catalase as well as activity of superoxide dismutase was not significantly different between the three species. This difference in catalase activity in the gills may also be responsible to the higher susceptibility of the yellowtail to Chattonella.Histological examination revealed that there were no edema formation in the gills when the initial Po_2 drop occurred early in Chattonella exposure. The only histological change observed in those gill samples was blockage of interfilamental spaces by mucus. Relationship between oxygen radical production by Chattonella and mucus secretion needs to be elucidated in the future research. Less