Susceptibility, behaviour, and retention of the parasitic salmon louse (Lepeophtheirus salmonis) differ with Atlantic salmon population origin

Abstract

Atlantic salmon populations across the world have diverse ecological and evolutionary histories, from wild anadromous or landlocked, to domestication and genetic modification. The natural host behaviours confer protection from infestation by ectoparasitic salmon lice Lepeophtheirus salmonis, yet whether genetic origin results in different behaviours and thus susceptibility to infestation is unknown. In common garden experiments, we tested antiparasite behaviours, susceptibility and retention of salmon lice in wild anadromous, wild landlocked, domesticated and genetically modified domesticated strains. Within domesticated strains, we tested two infestation histories (previously infested and naïve) and a new phenotype (albino colouring). Farmed stocks initially acquired 24%-44% higher levels of parasite density than the wild and landlocked strains. Burst swimming and displacement behaviours were higher in the domesticated groups, and jumping was more prevalent in the domesticated strains. At 34 days post-infestation, domesticated strains and the wild anadromous strain did not differ significantly from each other; however, landlocked salmon had increased infestation levels considerably. Domesticated strains lost ~20% (±9.9%-16.5%; 95% CI) of their initial parasite load, while parasite load increased by 5.5% (±30.1%) for wild salmon and 20.1% (±28.5%) in landlocked salmon. This study provides early evidence for diverged host-parasite interactions associated with domestication in this system.

Gene Expression Response to Sea Lice in Atlantic Salmon Skin: RNA Sequencing Comparison Between Resistant and Susceptible Animals

“…Further, Caligus infection is known to induce increased enzyme activity in muscle tissue ( Vargas-Chacoff et al, 2017 ), and behavioral changes in the fish such as flashing and jumping are associated with ectoparasite removal ( Furevik et al, 1993 ; Magnhagen et al, 2008 ). It has been recently reported that inactivity or reduced swimming activity contribute to resistance to sea lice ( Bui, 2017 ), so it is possible that the high lice counts of susceptible fish in this study are due to higher activity levels with associated expression of muscle contraction related genes. In turn, high lice burden can provoke behavioral responses increasing fish activity, which results in the up-regulation of muscle genes, increasing the expression differences between resistant-passive-low lice fish and susceptible-active-high lice fish.…”

Where art thou louse? A snapshot of attachment location preferences in salmon lice on Atlantic salmon hosts in sea cages

“…In communal and single fish tanks, between 36% and 51% of mobile lice can be lost over 24 days (Hamre & Nilsen, 2011). Interestingly, farmed strains of salmon lost 27%–32% of attached lice over 34 days in tanks; however, this was not the case with wild and landlocked Atlantic salmon in the same tanks (Bui, Dalvin, et al, 2018), suggesting a genetic effect on lice developmental success or movement between hosts. However, experience in unspecific loss of lice over development and between replicate tanks has been reported as quite high and very variable (Bjørn & Finstad, 1998; Hamre, Glover, & Nilsen, 2009), but when infested fish are housed in an very controlled manner, variation and loss of lice can be almost eliminated (S. Dalvin, unpublished data).…”

The effect of temperature on ability of Lepeophtheirus salmonis to infect and persist on Atlantic salmon

“…Bui et al. (2018)). Retention of lice is highly dependent on the size and density of host fish and tank environment (Hamre et al., 2009) and therefore varies between experiments.…”

“…The remarkably low louse loss observed contrasts other reports. Whereas several experiments have observed little loss of lice in fish from infection to development of preadults (Bui et al., 2018; Fast et al., 2002; Grimnes & Jakobsen, 1996), considerable loss was reported during the preadult to early adult phase (Bjørn & Finstad, 1998; Bui et al., 2016; Dawson, Pike, Houlihan, & McVicar, 1997; Hamre et al., 2009; Hamre & Nilsen, 2011). Loss is likely to be a result of a number of processes including behaviour and response of the fish, accidental detachment of parasites from the fish through contact with tank surfaces, and movement of the parasite.…”

“…Salmon lice can be long‐lived and may remain on the host fish for extended periods of time under optimal conditions (Hamre et al., 2009); however, little concrete evidence is provided for the rate of loss of salmon lice after infection; it varies considerably between studies ranging from 30% to almost complete loss during development to adults (Bjørn & Finstad, 1998; Bui et al., 2018; Hamre et al., 2009; Hamre & Nilsen, 2011; Jones, Fast, Johnson, & Groman, 2007). Biological mechanisms have been explored whereby lice are likely to be lost from the host through host physiological or immune defences (Wagner, Fast, & Johnson, 2008), mate‐searching behaviours in mature stages (Stephenson, 2012), natural mortality, or some cumulative interaction of these factors (Bui, Oppedal, Nola, & Barrett, 2020).…”