Detection and diagnosis of the invasive swim bladder parasite, Anguillicola crassus, in American eels (Anguilla rostrata)

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University of New Brunswick


Anguillicola crassus is an invasive parasitic nematode that infects the swim bladder of American eels (Anguilla rostrata) throughout most of the eel’s native range. Declines in eel populations are attributed in part to A. crassus infection, with swim bladder damage impairing their survival and/or migration to the Sargasso Sea, where they migrate for reproduction. Hydroelectric dams on inland rivers, such as dams on the Wolastoq | Saint John River (W|SJR), New Brunswick, Canada, impede both upstream eel migration and parasite transmission. Thus, head ponds above dams could serve as refugia for stocking and translocation of parasite-free eels to support conservation initiatives. Based on eel life stage (pre-elvers, elvers, yellow) and month/location of eel collection, I assessed A. crassus infections in this system, using existing diagnostic tools (light microscopy and PCR/sequencing) as well as a new diagnostic methodology that I developed (autofluorescence microscopy). The high prevalence of A. crassus infection in elvers and yellow eels precludes their use in parasite-free translocation. However, the absence of infection in pre-elvers entering estuarine locations in March and April supports their use in conservation initiatives.