Abstract
The salmon louse Lepeophtheirus salmonis is a marine ectoparasite of wild and farmed salmon in the Northern Hemisphere. Infections of farmed salmon are of economic and ecological concern. Nauplius and copepodid salmon lice larvae are free-swimming and disperse in the water column until they encounter a host. In this study, we characterized the sublethal stress responses of L. salmonis copepodid larvae by applying a 38K oligonucleotide microarray to profile transcriptomes following 24 h exposures to suboptimal salinity (30–10 parts per thousand (‰)) or temperature (16–4 °C) environments. Hyposalinity exposure resulted in large-scale gene expression changes relative to those elicited by a thermal gradient. Subsequently, transcriptome responses to a more finely resolved salinity gradient between 30 ‰ and 25 ‰ were profiled. Minimal changes occurred at 29 ‰ or 28 ‰, a threshold of response was identified at 27 ‰, and the largest response was at 25 ‰. Differentially expressed genes were clustered by pattern of expression, and clusters were characterized by functional enrichment analysis. Results indicate larval copepods adopt two distinct coping strategies in response to short-term hyposaline stress: a primary response using molecular chaperones and catabolic processes at 27 ‰; and a secondary response up-regulating ion pumps, transporters, a different suite of chaperones and apoptosis-related transcripts at 26 ‰ and 25 ‰. The results further our understanding of the tolerances of L. salmonis copepodids to salinity and temperature gradients and may assist in the development of salmon louse management strategies.
Highlights
The salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) is an ectoparasite of wild and farmed salmonids (Salmo and Oncorhynchus spp.) in the Northern Hemisphere (Nagasawa et al 1993; Johnson et al 2004; Beamish et al 2009), genetically distinct varieties of L. salmonis occur in the Atlantic and Pacific Oceans (Yazawa et al 2008)
In British Columbia, Canada, adult Pacific salmon carry gravid L. salmonis when they return from the ocean to spawn
Lepeophtheirus salmonis obtained from seawater netpenreared Atlantic salmon Salmo salar in western British Columbia were maintained in cold aerated seawater during transport to the Pacific Biological Station, Nanaimo, BC
Summary
The salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) is an ectoparasite of wild and farmed salmonids (Salmo and Oncorhynchus spp.) in the Northern Hemisphere (Nagasawa et al 1993; Johnson et al 2004; Beamish et al 2009), genetically distinct varieties of L. salmonis occur in the Atlantic and Pacific Oceans (Yazawa et al 2008). There are a limited number of chemical treatment options (Johnson et al 2004), raising concerns for resistance development to commonly used treatments in Scotland, Norway and Atlantic Canada (Jones et al 1992; Denholm et al 2002; Boxaspen 2006; SEARCH 2006; Brooks 2009; Burridge et al 2010; Chang et al 2011). Other potential methods of control may include the use of cleaner wrasse, leaving farms to fallow, reducing synthetic light, and ensuring high water velocity at sites (SEARCH 2006)
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