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Characteristics of a sea louse (Caligus clemensi) epizootic in wild Pacific herring (Clupea pallasii)

September 15, 2023

We characterized a natural sea louse epizootic of Caligus clemensi and the effects of parasitism on Pacific herring Clupea pallasii in Port Angeles Harbor, WA, USA. Infestation prevalence on newly metamorphosed age 0 Pacific herring reached 100% prevalence by mid-August. At this time, the mean louse intensity was 4.6 lice/fish, and a positive correlation occurred between louse intensity and herring body length. The epizootic then waned, with infestation prevalence decreasing to less than 25% and the mean parasite intensity falling below 1 louse. While skin injuries were not detected, motile lice preferentially aggregated around head and anterior dorsal areas. However, louse tropism became evenly distributed over the body as the parasite intensity increased. Louse-induced mortality in herring was negligible in controlled experiments. These results indicate that Caligus clemensi epizootics reach high prevalence, but also fade from mid-summer to early fall. Due to the predominant presence of motile copepod stages, we suggest that the epizootic fades because lice complete their life cycle and dislodge from the host; however, multiple explanations for epidemic fading are possible.

Publication Year 2023
Title Characteristics of a sea louse (Caligus clemensi) epizootic in wild Pacific herring (Clupea pallasii)
DOI 10.1139/cjfas-2023-0070
Authors David James Páez, Jacob L. Gregg, Ashley MacKenzie, Sophie Amanda Hall, Paul Hershberger
Publication Type Article
Publication Subtype Journal Article
Series Title Canadian Journal of Fisheries and Aquatic Sciences
Index ID 70248516
Record Source USGS Publications Warehouse
USGS Organization Western Fisheries Research Center