Laboratory exposure studies to assess impacts of sea lice Caligus clemensi infections on juvenile Sockeye salmon
Sea lice, a naturally occurring parasite, are managed by the Atlantic salmon aquaculture industry in British Columbia according to requirements set out by Fisheries and Oceans Canada (DFO) in the conditions of aquaculture licences. DFO works to ensure that infection levels on farms are below a set minimum to minimize the potential exposure of wild and farmed fish to sea lice.
Research shows that in the Strait of Georgia, over 70% of juvenile Sockeye and other salmon are infected with sea lice of two species: Lepeophtheirus salmonis and Caligus clemensi. Comparative laboratory experiments confirmed that juvenile Sockeye salmon are susceptible to infection with L. salmonis. Compared to other species of salmon, Sockeye salmon are more likely to develop severe skin lesions, osmoregulatory, imbalance and increased susceptibility to virus infections – all of which are related to their inability to mount an adequate defense response in the skin following infection with sea lice.
The majority of previous research has focused on susceptibility and defense responses to L. salmonis, with comparatively little known about the relative susceptibility of Sockeye salmon to C. clemensi. This study further investigated the physiological effects of single and mixed infections in order to establish a lethal threshold of C. clemensi infection, and to characterise defense response mechanisms in Sockeye salmon. The results of this study provided data in support of a more balanced assessment of the impact of sea lice on juvenile Pacific salmon, in particular Sockeye salmon.
The combined low availability and poor culture performance of Caligus clemensi contributed to the early termination of this project.
Pink salmon were examined 7 and 14 days after exposure to adult C. clemensi. No lice were observed. Failure to detect lice following experimental exposure of pink salmon was likely due to the high mobility of the parasite which readily detaches from the host making counting and collection difficult.
2015 - 2016
Amelia Mahony, Biologist, Fisheries and Oceans Canada, Pacific Biological Station, Pacific Region
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