U.S. Geological Survey - Western Fisheries Research Center, Marrowstone Marine Field Station, 616 Marrowstone Point Road, Nordland, WA 98358, USA.
Dis Aquat Organ. 2022 Jul 14;150:61-67. doi: 10.3354/dao03677.
In recent decades, evidence has accumulated to suggest that the widespread and highly variable parasite Ichthyophonus hoferi is actually a species complex. Highly plastic morphology and a general lack of defining structures has contributed to the likely underestimate of biodiversity within this group. Molecular methods are a logical next step in the description of these parasites, but markers used to date have been too conserved to resolve species boundaries. Here we use mitochondrial encoded cytochrome-c oxidase (MTCO1) gene sequences and phylogenic analysis to compare Ichthyophonus spp. isolates from several marine and anadromous fish hosts. The resulting phylogeny displays lineage separation among isolates and possible host/niche segregation not previously described. The parasite type that infects Pacific herring Clupea pallasii, Atlantic herring C. harengus, Atlantic salmon Salmo salar, and Pacific staghorn sculpin Oligocottus maculosus (Clade A) is different from that which infects Chinook salmon Oncorhynchus tshawytscha, walleye pollock Gadus chalcogrammus, Greenland halibut Reinhardtius hippoglossoides, and Pacific halibut Hippoglossus stenolepsis (Clade B). MTCO1 sequences confirmed the presence of a more divergent Ichthyophonus sp. isolated from American shad Alosa sapidissima in rivers of eastern North America (Clade C), while American shad introduced to the Pacific Ocean are infected with the same parasite that infects Pacific herring (Clade A). Currently there are no consensus criteria for delimiting species within Ichthyophonidae, but MTCO1 sequences hold promise as a potential species identifying marker and useful epizootiological tool.
近几十年来，有证据表明广泛存在且高度多变的寄生虫 Ichthyophonus hoferi 实际上是一个种复合体。高度可塑性的形态和普遍缺乏定义结构的特点，导致该群体的生物多样性可能被低估。分子方法是描述这些寄生虫的逻辑下一步，但迄今为止使用的标记物过于保守，无法解决物种界限问题。在这里，我们使用线粒体编码细胞色素-c 氧化酶（MTCO1）基因序列和系统发育分析来比较来自几种海洋和洄游性鱼类宿主的 Ichthyophonus 分离株。得到的系统发育显示出分离株之间的谱系分离，以及以前未描述的可能的宿主/生态位隔离。感染太平洋鲱 Clupea pallasii、大西洋鲱 C. harengus、大西洋鲑 Salmo salar 和太平洋鹿角杜父鱼 Oligocottus maculosus 的寄生虫类型（Clade A）与感染奇努克鲑 Oncorhynchus tshawytscha、大眼狮鲈 Gadus chalcogrammus、格陵兰比目鱼 Reinhardtius hippoglossoides 和太平洋比目鱼 Hippoglossus stenolepsis 的寄生虫类型（Clade B）不同。MTCO1 序列证实了从北美东部河流中的美洲西鲱 Alosa sapidissima 中分离出的更具差异性的 Ichthyophonus sp.（Clade C）的存在，而引入太平洋的美洲西鲱则感染了与感染太平洋鲱相同的寄生虫（Clade A）。目前，Ichthyophonidae 内种的界定尚无共识标准，但 MTCO1 序列有望成为潜在的种识别标记和有用的流行病学工具。
