By Larry Reynolds
Several species of sea lice have become a growing challenge for salmon farming around the world. In a recent article published in Animal Frontiers authors Okechukwu Igboeli, John Burka, and Mark Fast discuss both the current challenges as well as the therapeutic and management strategies for controlling this devastating parasite.
Aquaculture production has expanded rapidly since 2001 and currently accounts for 40% of world fish production; in addition, fin fish such as salmon (as opposed to molluscs and crustaeans, for example) represent two-thirds of world aquaculture production (ftp://ftp.fao.org/FI/news/GlobalAquacultureProductionStatistics2011.pdf). Production of salmon by aquaculture is no exception and has increased dramatically in the past 20+ years (http://www.fao.org/fishery/culturedspecies/Salmo_salar/en#tcNA00B1).
Atlantic salmon (Salmo salar) is the most intensively farmed fish, with Canada and Chile leading production in North America, and Ireland, Norway, and Scotland leading in Northern Europe. For Atlantic North American and Northern European salmon farming, Lepeophtheirus salmonis and Caligus elongatus are the major species of sea lice infecting salmon. For Pacific North America and Chile, other species are more prominent. Although the article by Igboeli et al. focuses on L. salmonis, the strategies that are outlined likely have implications for parasite control in other farmed salmonids (for example, Pacific salmon species, sea trout, and charr; Costello, J Fish Diseases 32:115-18, 2009).
Sea lice infection is linked to reduced growth rate (in part due to poor efficiency of feed utilization), loss of scales, hemorrhaging of eyes and fins, and, importantly, increased secondary infections in farmed salmon (Costello, 2009). As one of the authors (Fast) stated via email, “While there has been debate over … sea lice … as a vector for this [orthomyxovirus infectious salmon anemia (ISAv)] virus, lice infection does also affect host ability to respond to this and other infections (i.e, through stress, immunomodulation, etc.) …” Resistance to parasiticides also has emerged as a major issue in control of sea lice, and the cost of therapeutics including parasiticides contributes to economic loss (Costello, 2009). Moreover, it has been suggested that sea lice from salmon farms may contribute to increased incidence of sea lice infection in wild salmon populations (http://www.atlanticsalmontrust.org/assets/ast-sea-lice-impacts-review.pdf). Thus, production losses from sea lice infection have major socioeconomic impact.
One alternative strategy is to move farming of salmon and other marine fish to land-based systems. However, Fast argues that production needs “…cannot be met through land-based or self-contained environments [due to issues related to] water demand, effluent treatment and release, and overall ecological and economic footprints …”
All of this points to the critical need not only for more integrated sea lice management strategies but also for increased research aimed at alternative approaches to control of this pest, such as stimulating host immune defense mechanisms or genetic selection of resistant salmon lines. Without such forward-looking strategies, this major source of fish production may fail.
This article, “Lepeophtheirus salmonis: a persisting challenge for salmon aquaculture,” is available in the January 2014 issue of Animal Frontiers, and can be found at http://www.animalfrontiers.org/content/4/1/22.abstract.
University of Prince Edward Island
ASAS Media Communications
Keywords: aquaculture, salmon farming, parasites, sea lice, control strategies