Development of the use of wrasse to control sea lice on salmon farms in Ireland

Abstract

Abstract. Developments in the use of wrasse as cleaner-fish in the control of sea lice (Lepeophtheirus salmonis, Caligus elongatus) in Ireland are reviewed. Corkwing, Symphodus melops, and goldsinny, Ctenolabrus rupestris, have controlled L. salmonis (<1 louse per salmon) on commercial farms. C. rupestris and rockcook, Centrolabrus exoletus, removed both adult and chalimus C. elongatus in aquarium trials. No egg-bearing lice were ever found on salmon in cages with wrasse, and numbers of mobile lice were maintained at <1 per salmon smolt. Wrasse are fished using shrimp pots, optimally set for about 2 h. The fishery is seasonal and limited to >10cm wrasse occurring close to the farm, and distant from other farms. Localized reductions in the body length and numbers of wrasse have been detected in the second year of fishing in two areas respectively. Due to the fishery limitations and high fecundity of wrasse, impacts on wrasse populations should remain localized. All wrasse populations fished are screened for microbial diseases, and protozoan and metazoan parasites. Results are typical for wild marine fish but metazoan skin parasites are rare. No pathogens, including tests with an Aeromonas sp. found in wrasse, have been found to be transferable to salmon. Wrasse are the only effective and continuous method of sea lice control legally available. Research efforts should be directed towards improving the availability, pathogen-free status, and husbandry of wrasse, to enable cleaner-fish technology to be more widely and efficiently utilized.