Towards a sustainable fishery and use of cleaner fish in salmonid aquaculture

Parasitic salmon lice cause great economic losses in the aquaculture of Atlantic salmon and rainbow trout. It also has a significant impact on wild populations of salmonids, particularly sea trout in areas with aquaculture activity. Several pharmaceuticals have been used for treatment of salmon lice infestations, but over time the lice have developed resistance to these treatments, and there is a growing concern regarding the environmental impact of chemical and pharmaceutical treatments on non-target organisms. Consequently, there has been a strong incentive to find alternative methods for de-lousing. The use of cleaner fish, which pick lice from the skin of infested salmonids, has become an important tool to fight lice. Lumpfish and several species of wrasses are used as cleaner fish. There are extensive fisheries for wrasses in the UK, along the Swedish west coast and in Norway. In addition, there is aquaculture of ballan wrasse and lumpfish in Norway, and lumpfish in the UK and Iceland. The fisheries and use of cleaner fish have evolved relatively fast, whereas scientific data collection, as well as the development of a regulatory framework, has lagged behind. Challenges linked to poor welfare, transmission of diseases and changes in the genetic structure of local populations as a result of translocations have raised questions regarding the sustainability of the current cleaner fish practice. Both ballan wrasse and lumpfish are relatively new as farmed species, and as new species in aquaculture, there are knowledge gaps that must be filled. Research on different aspects for each of the two species has recently increased to address problems and prepare the fish for a life as cleaner fish in sea cages. There is also an increase in research that aims to increase survival and welfare of cleaner fish. There is still a way to go, but information from farmers who have good results show that it should be possible to achieve improvement. A wide range of research projects and studies have been initiated in Scandinavia and the UK over the last decade. In order to facilitate a more rapid spread and implementation of good management solutions that are based on knowledge of the species, it is therefore important that scientists and regulating authorities in different institutions and countries have a common knowledge-base and are collaborating efficiently. This report presents the state-of-knowledge on the biology of cleaner fish, the challenges regarding environmental impacts of fishing, translocation and how management have dealt with the fisheries in the Nordic countries. The development and challenges related to the use and welfare of cleaner fish in captivity are presented and discussed. Based on our shared expert knowledge, we hopefully provide management recommendations on how the fisheries and use of cleaner fish can become more sustainable. A sustainable fishery should allow the target species to replenish and have no long-term or permanent negative changes on ecosystem diversity, function, or productivity. A sustainable practice should minimize the harm and death of cleaner fish, as well as escapement and the associated risks; including transfer of new diseases to new species and areas, and irreversible genetic changes in the wild populations that reduce fitness or adaptability. The report also identifies data gaps that may be filled with future, hopefully collaborative, research or monitoring activities. Although there is an active collaboration between Swedish and Norwegian cleaner fish researchers there is still a considerable potential for improvement through exchange of knowledge and experiences between scientist and managers in Norway, Sweden and the UK, as well as with those in other countries with developing or emerging fisheries for wrasses, like Denmark