Effect of Nanophyetus salmincola and Bacterial Co-Infection on Mortality of Juvenile Chinook Salmon

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The article is copyrighted by the American Fisheries Society and published by Taylor & Francis. It can be found at: http://www.tandfonline.com/toc/uahh20/currentThe freshwater trematode Nanophyetus salmincola has been demonstrated to impair salmonid immune function\ud and resistance to the marine pathogen Vibrio anguillarum, potentially resulting in ocean mortality. We examined\ud whether infection by the parasite N. salmincola similarly increases mortality of juvenile Chinook Salmon Oncorhynchus\ud tshawytscha when they are exposed to the freshwater pathogens Flavobacterium columnare or Aeromonas\ud salmonicida, two bacteria that juvenile salmonids might encounter during their migration to the marine environment.\ud We used a two-part experimental design where juvenile Chinook Salmon were first infected with N. salmincola\ud through cohabitation with infected freshwater snails, Juga spp., and then challenged with either F. columnare or\ud A. salmonicida. Cumulative percent mortality from F. columnare infection was higher in N. salmincola-parasitized\ud fish than in nonparasitized fish. In contrast, cumulative percent mortality from A. salmonicida infection did not\ud differ between N. salmincola-parasitized and nonparasitized groups. No mortalities were observed in the N. salmincola-\ud parasitized-only and control groups from either challenge. Our study demonstrates that a relatively high mean\ud intensity (>200 metacercariae per posterior kidney) of encysted N. salmincola metacercariae can alter the outcomes\ud of bacterial infection in juvenile Chinook Salmon, which might have implications for disease in wild fish populations