Gregg J L, Grady C A, Friedman C S, Hershberger P K
Western Fisheries Research Center, US Geological Survey, Nordland, WA 98358, USA.
Dis Aquat Organ. 2012 Jun 13;99(2):139-44. doi: 10.3354/dao02458.
The parasite Ichthyophonus is enzootic in many marine fish populations of the northern Atlantic and Pacific Oceans. Forage fishes are a likely source of infection for higher trophic level predators; however, the processes that maintain Ichthyophonus in forage fish populations (primarily clupeids) are not well understood. Lack of an identified intermediate host has led to the convenient hypothesis that the parasite can be maintained within populations of schooling fishes by waterborne fish-to-fish transmission. To test this hypothesis we established Ichthyophonus infections in Age-1 and young-of-the-year (YOY) Pacific herring Clupea pallasii (Valenciennes) via intraperitoneal (IP) injection and cohabitated these donors with naïve conspecifics (sentinels) in the laboratory. IP injections established infection in 75 to 84% of donor herring, and this exposure led to clinical disease and mortality in the YOY cohort. However, after cohabitation for 113 d no infections were detected in naïve sentinels. These data do not preclude the possibility of fish-to-fish transmission, but they do suggest that other transmission processes are necessary to maintain Ichthyophonus in wild Pacific herring populations.
寄生虫艾氏异孢虫在北大西洋和太平洋的许多海洋鱼类种群中呈地方流行性。饵料鱼很可能是高营养级捕食者的感染源；然而，维持艾氏异孢虫在饵料鱼种群（主要是鲱科鱼类）中的传播过程尚未得到充分了解。由于尚未确定中间宿主，因此有人提出一种简便的假设，即该寄生虫可通过水体中的鱼对鱼传播在群居鱼类种群中得以维持。为了验证这一假设，我们通过腹腔注射在1龄和当年幼鱼（YOY）太平洋鲱（Clupea pallasii，瓦朗谢讷）中建立了艾氏异孢虫感染，并在实验室中将这些供体鱼与未感染的同种鱼（哨兵鱼）放在一起饲养。腹腔注射使75%至84%的供体鲱鱼受到感染，这种感染导致当年幼鱼出现临床疾病并死亡。然而，在共同饲养113天后，未在未感染的哨兵鱼中检测到感染。这些数据并不排除鱼对鱼传播的可能性，但确实表明，在野生太平洋鲱种群中维持艾氏异孢虫感染需要其他传播过程。
