Susceptibility of Pink salmon (Oncorhynchus gorbuscha) to Caligus elongatus and Lepeophtheirus salmonis and effect on some skin inflammatory cytokines

Abstract

Infections with Caligid ectoparasites such as Lepeophtheirus salmonis and Caligus elongatus represents one of the greatest challenges for the Norwegian aquaculture industry with large associated cost for treatment and control since these parasites negatively impact animal welfare of the Atlantic salmon and may result in early deaths of their salmonid hosts. The parasites feed upon the skin and mucus of susceptible species, which in turn imposes increased osmoregulatory challenges, stress, and facilitation of secondary infection with subsequent death for their host fish. Different species of salmonids display different susceptibility towards infections with these parasites, with resistant species displaying a strong immune response to rid itself of the lice. One of the species which display a heightened resistance towards infections is the pink salmon (Oncorhynchus gorbuscha) which has recently established itself as an invasive species in Norway. This species is known as highly resistant to infection with L. salmonis although whether this species could rid itself of the non-native generalist parasite C. elongatus was unknown and laid the foundation for this study with a main aim to experimentally assess susceptibility to C. elongatus copepodids and their subsequent survival and interaction with the host. We report that the pink salmon is susceptible to infection with C. elongatus genotype I and our result indicate the pink salmon is a viable host for this parasite to complete its life cycle on. The pink salmon displayed similar pathology and clinic to what has been previously described for other salmonid fish, with erratic swimming, decreased appetite, and development of sores. Additionally, we report an upregulation of inflammatory mediators of IL-4/13, IL-8, IL-1β and CCL20 in the skin beneath lice attachment, although our transcriptional analysis suffers from high experimental variation.