Is widespread cleanerfish use driving the evolution of transparent lice? Examining pigmentation in Lepeophtheirus salmonis
Parasitic salmon lice (Lepeophtheirus salmonis) are the biggest challenge to environmentally sustainable salmonid aquaculture globally. This species also displays high evolutionary potential, as demonstrated by its rapid development of resistance to delousing chemicals. Farms now use a range of non-chemical prevention and control techniques, including cleaner fish which eat lice directly off the salmon. Anecdotal reports from farms suggest that where cleaner fish are used, lice are beginning to appear less pigmented, and thus less visible to cleaner fish. However, do these observations reflect a plastic (environmental) or adaptive (genetic) response? The aim of this study is to estimate the relative importance of genetics and environmental exposure on the variation in pigmentation in salmon louse populations.
This experiment is expected to cause mild to moderate distress for the 200 infected salmon as a result of lice infestation. The salmon will not be exposed to any other stressors, and we will aim for a lice infestation of 10 per fish. However, due to variability in the infection success, our upper threshold for lice infestation will be 30 lice per fish, a commonly accepted limit to maintain acceptable welfare.
More than 60 million cleanerfish were deployed in salmon cages in 2019. If genotype has a significant influence on color (i.e. heritability is high), then there is the potential for louse populations to evolve in response to selection, leading to reduced cleaner fish effectiveness. If the observed variation in lice pigmentation is primarily plastic and driven by environmental exposure, then evolution of reduced pigmentation in response to selection by cleaner fish is unlikely. Thus, in addition to improving our basic biological understanding of L. salmonis, these results will have substantial commercial implications for producers of both salmon and cleaner fish.
200 Atlantic salmon (Salmo salar) post-smolts weighing at least 300 grams will be utilized in this study.
L. salmonis are a parasitic organism, and require a host to develop beyond the copepodid stage. For that reason, salmon are required in this study. The number of salmon used (200) was chosen to balance the number of individuals used in the trial against the distress caused to each individual as a result of lice infestation.
This experiment is expected to cause mild to moderate distress for the 200 infected salmon as a result of lice infestation. The salmon will not be exposed to any other stressors, and we will aim for a lice infestation of 10 per fish. However, due to variability in the infection success, our upper threshold for lice infestation will be 30 lice per fish, a commonly accepted limit to maintain acceptable welfare.
More than 60 million cleanerfish were deployed in salmon cages in 2019. If genotype has a significant influence on color (i.e. heritability is high), then there is the potential for louse populations to evolve in response to selection, leading to reduced cleaner fish effectiveness. If the observed variation in lice pigmentation is primarily plastic and driven by environmental exposure, then evolution of reduced pigmentation in response to selection by cleaner fish is unlikely. Thus, in addition to improving our basic biological understanding of L. salmonis, these results will have substantial commercial implications for producers of both salmon and cleaner fish.
200 Atlantic salmon (Salmo salar) post-smolts weighing at least 300 grams will be utilized in this study.
L. salmonis are a parasitic organism, and require a host to develop beyond the copepodid stage. For that reason, salmon are required in this study. The number of salmon used (200) was chosen to balance the number of individuals used in the trial against the distress caused to each individual as a result of lice infestation.