Occurrence of pathogens in Pacific lamprey ( Entosphenus tridentatus )

Pacific lamprey ( Entosphenus tridentatus ) is a First Food of Native Americans. Declines in lamprey abundance due to dam construction and habitat loss have curtailed traditional harvest opportunities. Artificial propagation is an emerging recovery tool for this imperiled species, and other lamprey species in Finland and Japan. To manage disease risk at prospective lamprey hatcheries, it is critical to understand the pathogens and parasites most likely to affect lamprey and other fish, both in culture and in the wild. We assembled data from regional fish health laboratories to assess pathogen prevalence in Pacific lamprey sampled from various sources (518 adults, 275 larvae, and one juvenile). In adults, Aeromonas salmonicida was identified using standard health screening methods in 0–69% of dead lamprey samples submitted, but no other pathogens were typically observed. All larvae were negative for bacterial and viral infections, and larvae experimentally exposed to A. salmonicida showed no infection or mortality. Conspicuously absent were detailed health assessments for metamorphosed larvae (juveniles). However, external examinations of over 20,000 juveniles captured at dams on the lower Columbia River indicated that they are susceptible to fungal infection in warm water conditions (> 12 °C), which can lead to mortality. To fully evaluate the disease risk associated with lamprey culture, directed research is needed along with standardized health screenings of lamprey at all life stages. Control of A. salmonicida , the etiological agent for furunculosis, will be a top priority for Pacific lamprey use, as this was the only pathogen regularly identified in this species.