The constituents released from sea lice (Lepeophtheirus salmonis) in the presence of salmonid mucus

Sea lice (Lepeophtheirus salmonis, Kroyer) are a major pathogen of farmed Atlantic salmon (Salmo salar). To obtain a better understanding of the host-parasite relationship protease secretions of L. salmonis into mucus collected from susceptible hosts (Atlantic salmon and rainbow trout, Oncorhynchus mykiss), a resistant salmonid (coho salmon, Oncorhynchus kisutch) and a non-salmonid (winter flounder, Pseudopleuronectes americanus) were compared. Protease zymography of mucus from these fish following incubation with live lice revealed the presence of L. salmonis derived low molecular weight proteases more frequently in Atlantic salmon and rainbow trout, compared to coho salmon or flounder. The differences in L. salmonis protease secretion in response to mucus from different host species may partially explain why coho salmon are more resistant to infection.