The development of the Norwegian wrasse fishery and the use of wrasses as cleaner fish in the salmon aquaculture industry

Abstract

Norway leads the world aquaculture production of Atlantic salmon Salmo salar and farmed Norwegian Atlantic salmon is currently consumed around the globe. However, sea lice infestation is a major problem faced by the salmon aquaculture industry in Norway and elsewhere. The use of wild-caught cleaner fish, mainly wrasses, has been recommended over the other available methods as the most economical and environmentally friendly option to control sea lice infestation in salmon farming. Here, we review the development of the Norwegian wrasse fishery and the use of wrasses as cleaner fish. In this document, we address the sea lice problem and introduce the main wrasse species employed as cleaner fish, document the cleaning behaviour of wrasses, present the development of a new wrasse fishery associated with the salmon aquaculture industry, and finally, we identify the main challenges associated with the intensive use of wild-caught cleaner wrasses and provide some insight for future directions of the wrasse fishery and further development of aquaculture techniques to supply salmon facilities with domesticated cleaner fish.

Embryonic development in corkwing wrasse, Symphodus melops

“…Indeed, the small size of the larvae at the time of mouth opening in corkwing and goldsinny wrasses has been a major constraint to developing rearing techniques for these species. Instead, efforts have been directed toward the larger ballan wrasse, which is the only wrasse species farmed commercially (Blanco Gonzalez & de Boer, ). The development of aquaculture techniques to produce large numbers of domesticated wrasses may create new opportunities to mitigate the intensive fishing pressure on wild wrasses, as well as the ecological and genetic risks associated with translocated fish populations (Blanco Gonzalez & de Boer, ).…”

“…In 2017, approximately 20 million wild wrasses were used by the salmon industry (Statistics Norwegian Directorate of Fisheries: http://www.fiskeridir.no/Akvakultur/Statistikk-akvakultur/Akvakulturstatistikk-tidsserier/Rensefisk) despite little knowledge about their biology (Blanco Gonzalez & de Boer, ). Additional concerns revolve around the possibility that translocated wrasses with distinct genetic profiles to recipient populations (Blanco Gonzalez, Knutsen, & Jorde, ; Jansson et al, ) may escape (Espeland et al, ) and spawn viable eggs that may survive the colder temperatures experienced in northern regions (Blanco Gonzalez & de Boer, ; Faust, Halvorsen, Andersen, Knutsen, & André, ). Eventually, they could establish a genetically distinct population and/or compromise the viability and evolutionary potential of the species (Blanco Gonzalez et al, ; Faust et al, ).…”

“…The use of cleaner fish as biological treatment to combat sea lice infestation in Norwegian salmon farming has reached unprecedented levels (Blanco Gonzalez & de Boer, 2017), with more than 54 million fish used in 2017 (Statistics Norwegian Directorate of Fisheries: http://www.fiskeridir.no/Akvakultur/Statistikk-akvakultur/ Akvakulturstatistikk-tidsserier/Rensefisk). At present, five main species are used as cleaner fish, namely, corkwing, Symphodus melops; goldsinny, Ctenolabrus rupestris; ballan, Labrus bergylta; rock cook, Centrolabrus exoletus, wrasses; and lumpfish, Cyclopterus lumpus (Deady, Varian, & Fives, 1995;Skiftesvik, Bjelland, Durif, Johansen, & Browman, 2013).…”

“…The abundance of wild wrasses in Norway has increased drastically over the last decades (Barceló, Ciannelli, Olsen, Johannesen, & Knutsen, 2016), a trend that appears associated with the warmer sea water temperatures registered (Knutsen et al, 2013). As a result, millions of wrasses are fished in warmer southern regions and annually translocated to salmon farms located in colder northern areas where local stocks are not large enough to support their high demand (Blanco Gonzalez & de Boer, 2017). The intensive fishing pressure on wrasses raised concerns about the sustainability of the fishery, and a maximum fishing quota was implemented for the first time in 2016.…”

Interbreeding between local and translocated populations of a cleaner fish in an experimental mesocosm predicts risk of disrupted local adaptation

“…Sea lice infestation is a major burden for the aquaculture industry causing high salmon mortalities and large economic losses (Blanco Gonzalez & de Boer, 2017;Iversen, 2016). The use of wrasses as cleaner fish has been proposed to be the most economical and environmental friendly solution to combat sea lice infestation (Liu & Bjelland, 2014), despite high mortalities at low temperatures (Bjelland, Simensen, & Kvenseth, 1996;Costello, 1991;Sayer, Reader, & Davenport, 1996).…”