Impacts of Multispecies Parasitism on Juvenile Coho Salmon (Oncorhynchus kisutch) in Oregon

NEWS COVERAGE: A news release based on this journal publication, which is written for a lay audience and has been approved by an author of the study, is available online: http://bit.ly/nGB6XDFULL TEXT: This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/aquaculture/. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.We are studying the impacts of parasites on threatened stocks of Oregon coastal coho\ud salmon (Oncorhynchus kisutch). In our previous studies, we have found high infections of\ud digeneans and myxozoans in coho salmon parr from the lower main stem of West Fork Smith\ud River (WFSR), Oregon. In contrast parr from tributaries of this river, and outmigrating smolts,\ud harbor considerably less parasites. Thus, we have hypothesized that heavy parasite burdens in\ud parr from this river are associated with poor overwintering survival. The objective of the current\ud study was to ascertain the possible effects these parasites have on smolt fitness. We captured parr\ud from the lower main stem and tributaries of WFSR and held them in the laboratory to evaluate\ud performance endpoints of smolts with varying degrees of infection by three digeneans\ud (Nanophyetus salmincola, Apophallus sp., and neascus) and one myxozoan (Myxobolus\ud insidiosus). The parameters we assessed were weight, fork length, growth, swimming stamina,\ud and gill Na+,K+36 -ATPase activity. We repeated our study on the subsequent year class and with\ud hatchery reared coho salmon experimentally infected with N. salmincola. The most significant\ud associations between parasites and these performance or fitness endpoints were observed in the\ud heavily infected groups from both years. We found that all parasite species, except neascus, were\ud negatively associated with fish fitness. This was corroborated for N. salmincola causing reduced\ud growth with our experimental infection study. Parasites were most negatively associated with\ud growth and size, and these parameters likely influenced the secondary findings with swimming\ud stamina and ATPase activity levels