Journal of Aquaculture Research & Development

Abstract

Mechanisms of Resistance among Salmon to the Parasitic Copepod Lepeophtheirus salmonis

Simon RM Jones

The purpose of this paper is to review the current knowledge of salmonid defence responses to Lepeophtheirus salmonis. The salmon louse L. salmonis is an important pest of economically valuable salmonids in seawater throughout the northern hemisphere. Treatment of salmon lice on cultured salmon often fails in regions where the parasite has developed resistance to commonly used therapeutants. The development of efficacious vaccines is hampered by limited knowledge of parasite antigens that elicit protective immunity and a poor understanding of defence responses mounted by the salmonid host. Infection kinetics indicate a wide range of susceptibilities to L. salmonis among salmon species: juvenile coho and pink salmon are relatively resistant whereas Atlantic and chum salmon are susceptible. Innate resistance is linked to the speed and intensity of local inflammatory reactions at the site of infection. Conversely, susceptibility is related to an absence of these reactions and in Atlantic salmon is mediated in part by hypersecretion by the parasite of prostaglandin E2 and other compounds. Transcriptomic analysis shows that the susceptible salmonid response is characterised by cell stress, tissue remodelling and diminished immunological responsiveness during infection. In contrast, there is evidence of cell motility, somatic growth and immuncompetence among resistant salmon following infection. Future research should apply a combination of genomic, proteomic and immunological studies to better understand defence mechanisms among susceptible and resistant salmonids.