The rise and fall of cleaner fish use in Norwegian salmon farming

Using cleaner fish to remove parasitic lice from farmed salmonids was heralded as an effective, environmentally sound method. However, we contend that the use of cleaner fish was adopted too rapidly and lacked sound evidence on their efficacy and welfare at commercial scale. Cleaner fish use (wild-caught wrasse, and farmed lumpfish and ballan wrasse) peaked in 2019, but has since declined. Four main factors likely contributed to the decline: (1) uncertainty surrounding efficacy; (2) poor welfare and high mortality rates; (3) availability of new preventative and control methods; and (4) changes in regulations and enforcement. Despite strategies employed by farmers to improve welfare, cleaner fish show limited adaptability to life in sea-cages. Since 1998, over half a billion cleaner fish have been deployed in sea-cages in Norway, with experimental and farmer-reported evidence indicating consistently poor welfare. Based on uncertain efficacy, poor welfare, and our assessment that improvements to cleaner fish use will not reduce mortality rates to the Norwegian government’s targets, we recommend that the use of lumpfish and wild-caught wrasse be phased out. Furthermore, as farmed ballan wrasse are regarded by some farmers as effective delousers, we recommend that the Norwegian salmon industry secure their welfare, reduce mortality levels to 5%, and demonstrate efficacy through multiple commercial-scale trials by 2029 or discontinue their use. The rise and fall of cleaner fish in Norway demonstrates why thorough research at the correct scale is required for all new techniques and technologies before they are widely deployed.