Defence against the Dark Arts: Mechanisms of Resistance among Salmon to the Parasitic Copepod Lepeophtheirus salmonis

Abstract

IntroductionCopepods belonging to the family Caligidae, referred to as sea lice, are ectoparasites of marine fishes. All sea lice share similar life cycles including nauplius stages and an infective copepodid stage that disperse in the plankton while subsisting on endogenous lipids. Once settled onto a suitable host, the copepodid moults through four chalimus stages that are tethered to the host with a frontal filament. Depending on species, the parasite further develops through one or two preadult stages to the adult stage which are untethered and mobile on the host. Much of the damage caused by parasitic copepods is related to attachment to the host ( Figure 1) and feeding behaviour: the parasites graze on host tissues that range from mucus, cells of the epidermis, dermis or subcutaneous tissues. The more invasive feeding behaviours are associated with the larger developmental stages.Species of sea lice parasitic on salmonid fishes are well described pests in marine aquaculture and in the northern hemisphere include Lepeophtheirus salmonis (the salmon louse) and several species of Caligus [1][2][3][4]. Infections with L. salmonis incur annual costs to marine open netpen aquaculture in excess of 700M Euros in Norway, Scotland, Ireland and Canada [5]. In addition, infections with Caligus rogercresseyii are a significant economic burden to salmon aquaculture in Chile [6]. Management of sea lice infections in aquaculture depends on integrated husbandry schemes including chemotherapeutant intervention [7]. However, recent trends indicate a declining efficacy for many compounds used for treatment, suggesting that in several jurisdictions L. salmonis or C. rogercresseyii have developed tolerance or resistance to these compounds. The absence of commercially efficacious vaccines against sea lice reflects a lack of detailed knowledge of immunogenic parasite antigens that elicit protective immunity in salmonids. In addition, defence responses against parasitic copepods in fishes are poorly documented. A more thorough understanding of teleost defense mechanisms against sea lice will provide a rational basis for the development of novel management strategies. The purpose of this paper is to review the current understanding of salmonid defence responses to L. salmonis. AbstractThe 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 Atl...

Disease Resistance in Atlantic Salmon (Salmo salar): Coinfection of the Intracellular Bacterial Pathogen Piscirickettsia salmonis and the Sea Louse Caligus rogercresseyi

“…Additionally, we hypothesized that coinfection resistance is a heritable trait that does not correlate with resistance to a single infection of P. salmonis because salmonid defense mechanisms against bacteria and parasites are substantially different [46]. We present experimental evidence supporting both hypotheses for the interaction between Atlantic salmon, P. salmonis and C. rogercresseyi .…”

“…In this study, we hypothesized that coinfection with the sea louse C. rogercresseyi reduces the resistance of Atlantic salmon to P. salmonis because of the well-documented stress and depression of the immune system produced by sea lice infection in salmonids. Additionally, we hypothesized that coinfection resistance is a heritable trait that does not correlate with resistance to a single infection of P. salmonis because salmonid defense mechanisms against bacteria and parasites are substantially different [46] . We present experimental evidence supporting both hypotheses for the interaction between Atlantic salmon, P. salmonis and C. rogercresseyi .…”

Behaviour in the toolbox to outsmart parasites and improve fish welfare in aquaculture

“…These applications still require methodical testing of their efficacy and the potential negative welfare impacts before being considered for commercial use. Finally, interest in genomics and selective breeding of parasite-resistant salmon is increasing (Jones 2011;Y añez et al 2014;Gharbi et al 2015), but is still in the exploration phase.…”

Production, mortality, and infectivity of planktonic larval sea lice, Lepeophtheirus salmonis (Krøyer, 1837): current knowledge and implications for epidemiological modelling

“…In Atlantic salmon, initial infection by the copepodid can elicit a detectable transcriptomic host response within 1 day post infection (dpi) (Tadiso et al 2011) and some Pacific salmon species, e.g. juvenile coho, are able to mount a rapid and successful inflammatory response following infection (Johnson and Albright, 1992;Fast et al, 2002;Jones, 2011) that is capable of killing infecting copepodids within a few days. Atlantic salmon show a less developed inflammatory response and are generally considered to show a poor capacity for removing infecting copepodids (Johnson and Albright, 1992).…”