Kocan R M, Kocan A J, Reichley S R
School of Fisheries and Aquatic Science, University of Washington, Seattle, Washington, 98392, USA.
United States Navy, Conservation and Repair, Shipbuilding, 4101 Washington Avenue, Building 2, Code 162, Newport News, Virginia, 23607, USA.
J Aquat Anim Health. 2019 Dec;31(4):349-353. doi: 10.1002/aah.10087. Epub 2019 Oct 9.
The ingestion of infected prey is the most recognizable mode of transmission for Ichthyophonus, but because this mode of transmission is unidirectional from small prey fish to larger predators, it cannot sustain the parasite within or among populations nor does it explain transmission to planktivores. Recently, waterborne transmission was demonstrated in cultured Rainbow Trout Oncorhynchus mykiss, which could explain how the parasite is transmitted without piscivory. However, it is possible that this is an adaptation to aquaculture conditions, and may not occur among wild fish. To address this question, experiments were conducted to determine if a freshwater isolate of Ichthyophonus is infectious and pathogenic to marine species, as well as if transmission is possible between different marine species. Pacific Staghorn Sculpins Leptocottus armatus were fed a freshwater isolate of Ichthyophonus (clade C) and then housed with susceptible sentinel Rock Soles Lepidopsetta bilineata. Ninety two percent of the orally exposed sculpins and 30% of the sentinel soles were Ichthyophonus-positive at the end of the study, with 0% infected controls. These results demonstrate that a freshwater isolate of Ichthyophonus is infectious and pathogenic to marine species and can be transmitted in seawater in the absence of piscivory. It also provides a plausible mechanism for transmission to small prey fish and planktivores, as well as within a population of piscivores when infected prey is not available.
摄食受感染的猎物是鱼孢菌最常见的传播方式，但由于这种传播方式是从小型猎物鱼单向传播到大型捕食者，它无法在种群内部或种群之间维持寄生虫的传播，也无法解释其向浮游生物食性鱼类的传播。最近，在养殖的虹鳟Oncorhynchus mykiss中证实了水传播，这可以解释寄生虫在没有捕食鱼类的情况下是如何传播的。然而，这可能是对水产养殖条件的一种适应，在野生鱼类中可能不会发生。为了解决这个问题，进行了实验，以确定鱼孢菌的淡水分离株对海洋物种是否具有传染性和致病性，以及不同海洋物种之间是否可能发生传播。给太平洋角鲉Leptocottus armatus投喂鱼孢菌的淡水分离株（C类群），然后与易感的哨兵双线鳎Lepidopsetta bilineata一起饲养。在研究结束时，92%经口暴露的角鲉和30%的哨兵双线鳎鱼孢菌呈阳性，感染对照组为0%。这些结果表明，鱼孢菌的淡水分离株对海洋物种具有传染性和致病性，并且在没有捕食鱼类的情况下可以在海水中传播。这也为向小型猎物鱼和浮游生物食性鱼类传播，以及在没有感染猎物时在捕食性鱼类种群内部传播提供了一种合理的机制。
