Urawa S, Kusakari M
Hokkaido Salmon Hatchery, Fisheries Agency of Japan, Sapporo.
J Parasitol. 1990 Feb;76(1):33-40.
Experimental studies revealed that a freshwater ectoparasitic flagellate Ichthyobodo necator (Henneguy, 1883) could survive and reproduce in seawater after infected chum salmon fry, Oncorhynchus keta (Walbaum), were transferred directly from fresh water to 33% seawater. Minor morphological changes (slight reduction in body width, loss of twistlike wrinkles on body surface, and reduction in contractile vacuoles) were observed in the attached form of I. necator following transfer to seawater. The field survey also confirmed that I. necator occurs on chum salmon fry in seawater estuaries (salinity 17-34%) and in freshwater habitats. It was assumed that I. necator acquired salinity tolerance as a result of adapting to the migratory behavior of its anadromous host. Two morphologically similar bodonids, I. necator from chum salmon and Ichthyobodo sp. from marine Japanese flounder, Paralichthys olivaceus (Temminck and Schlegel), were differentiated by cross-infection experiments. Thus, the parasite from marine flounder should be regarded as a separate species from I. necator.
实验研究表明，将感染了淡水外寄生鞭毛虫鲺（Ichthyobodo necator，1883年亨内居命名）的大麻哈鱼仔鱼（Oncorhynchus keta，瓦尔鲍姆命名）直接从淡水转移到33%的海水中后，该鞭毛虫能够在海水中存活并繁殖。转移到海水中后，附着形态的鲺出现了一些微小的形态变化（体宽略有减小、体表螺旋状皱纹消失、伸缩泡减少）。实地调查也证实，鲺出现在海水河口（盐度17 - 34%）和淡水生境中的大麻哈鱼仔鱼身上。据推测，鲺由于适应溯河产卵宿主的洄游行为而获得了耐盐性。通过交叉感染实验区分了两种形态相似的波豆虫：来自大麻哈鱼的鲺和来自日本海产牙鲆（Paralichthys olivaceus，坦明克和施莱格尔命名）的波豆虫属（Ichthyobodo sp.）。因此，来自海产牙鲆的寄生虫应被视为与鲺不同的物种。
