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首页> 外文期刊>Journal of Parasitology >Post-mortem Sporulation of Ceratomyxa shasta (Myxozoa) After Death in Adult Chinook Salmon
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Post-mortem Sporulation of Ceratomyxa shasta (Myxozoa) After Death in Adult Chinook Salmon

机译：成年奇努克鲑鱼死亡后的Ceratomyxa shasta（Myxozoa）的死后孢子形成

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Ceratomyxa shasta (Myxozoa) is a common gastrointestinal pathogen of salmonid fishes in the Pacific Northwest of the United States. We have been investigating this parasite in adult Chinook salmon (Oncorhynchus tshawytscha) in the Willamette River, Oregon. In prior work, we observed differences in the pattern of development of C. shasta in adult salmon compared to juvenile salmon. Adult salmon consistently had large numbers of prespore stages in many of the fish that survived to spawn in the fall. However, myxospores were rarely observed, even though they were exposed and presumably infected for months before spawning. We evaluated the ability of C. shasta to sporulate following fish death because it is reported that myxosores are common in carcasses of Chinook salmon. We collected the intestine from 30 adult salmon immediately after artificial spawning and death (T-0). A total of 23 fish were infected with C. shasta based on histology, but only a few myxospores were observed in 1 fish by histology. Intestines of these fish were examined at T-0 and T-7 (latter held at 17 C for 7 days) using quantified wet mount preparations. An increase in myxospore concentrations was seen in 39% of these fish, ranging between a 1.5- to a 14.5-fold increase. The most heavily infected fish exhibited a 4.6-fold increase from 27,841 to 129,352 myxospores/cm. This indicates, supported by various statistical analyses, that under certain conditions presporogonic forms are viable and continue to sporulate after death in adult salmon. Considering the life cycle of C. shasta and anadromous salmon, the parasite may have evolved 2, non-mutually exclusive developmental strategies. In young fish (parr and smolts), the parasite sporulates shortly after infection and is released into freshwater from either live or dead fish before their migration to seawater, where the alternate host is absent. The second strategy occurs in adult salmon, particularly spring Chinook salmon, which become infected upon their return to freshwater in the spring or early summer. For several months throughout the summer, only prespore stages are observed in most fish, even at the time of spawning. But once the fish dies, environmental conditions experienced by C. shasta change and viable presporogonic stages are induced to sporulate. As the post-spawned fish occur in the upper reaches of rivers, the myxospores would be released in a freshwater environment that would provide a reasonable opportunity for them to encounter their freshwater polychaete hosts, which reside downstream.
机译：Ceratomyxa shasta（Myxozoa）是美国西北太平洋鲑鱼的常见胃肠道病原体。我们一直在俄勒冈州威拉米特河的成年奇努克鲑鱼（Oncorhynchus tshawytscha）中调查这种寄生虫。在先前的工作中，我们观察到成年鲑与幼鲑相比，梭状芽胞杆菌的发育模式有所不同。成年鲑鱼在许多幸存下来在秋天产卵的鱼中始终具有大量的孢子前期。但是，即使在产卵前暴露了粘孢子并可能感染了几个月，也很少观察到粘孢子。我们评估了C. shasta在鱼类死亡后形成孢子的能力，因为据报道，粘鳞菌在奇努克鲑鱼的尸体中很常见。在人工产卵和死亡（T-0）后，我们立即从30只成年鲑鱼中收集了肠道。根据组织学，总共有23条鱼感染了C. shasta，但是根据组织学，在1条鱼中仅观察到了少数粘孢子。使用定量湿装制剂在T-0和T-7（后于17 C保持7天）检查了这些鱼的肠。这些鱼中有39％的粘孢子浓度增加，增幅在1.5倍至14.5倍之间。受感染最严重的鱼表现出从27,841到129,352粘孢子/厘米的4.6倍增长。这表明，在各种统计分析的支持下，在某些情况下，成年鲑的前代形式是可行的，并在死亡后继续形成孢子。考虑到C. shasta和无性鲑的生命周期，该寄生虫可能已经进化为2，非互斥的发展策略。在幼鱼（parr和smolts）中，寄生虫在感染后不久就会形成孢子，并在迁移到海水之前从活鱼或死鱼释放到淡水中，而没有其他宿主。第二种策略发生在成年鲑鱼中，特别是春季的奇努克鲑鱼，它们在春季或初夏返回淡水后就受到感染。在整个夏天的几个月中，即使在产卵时，在大多数鱼中也只观察到孢子前期。但是，一旦鱼死亡，沙门氏菌所经历的环境条件就会发生变化，并且会形成活跃的前旋生阶段。由于产卵后的鱼出现在河流的上游，粘孢子将在淡水环境中释放，这将为它们遇到下游的淡水多毛hosts寄主提供一个合理的机会。

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