New Way Of Keeping Salmon Clean


Scottish fish farmers have embarked on a novel way of keeping salmon, reared for farming, clean – by using other, smaller fish to remove lice.

The idea is, the BBC has reported, to breed cleaner fish called wrasse. These fish feed on a common salmon parasite called sea lice.

Wrasses are a type of marine fish, distinguished by their bright colors. The strange sounding name the is derived from old Cornish dialect, a corruption of the word wragh, a which is based on the term for an old woman or hag.

Cleaner wrasses have a symbiotic relationship with other, often larger, fish. Here they groom the larger fish of lice and parasites, consuming what they manage to pick off as their primary food source. The larger fish (in this case, salmon) benefits through being free of parasites. The only risk from introducing cleaner fish is that they can sometimes go too far and start consuming healthy skin and scales from the bigger fish. For this reason, the introduction to salmon farms needs to be carefully controlled.

The target for the wrasses is sea lice, including the common genera Lepeophtheirus and Caligus. They are problematic parasites for fish farmers and those engaged in aquaculture. They are marine parasites that occur naturally on many different species of wild fish including wild adult salmon; the danger is when they infest farms. The parasites attach to gills or scales and proceed to feed off the fish. With young salmon, only an handful of lice are enough to kill the juvenile fish.

The idea has come about through a collaborative effort involving the Scottish Aquaculture Innovation Center (funded by the Scottish government), University of Stirling, and a seafood company called Marine Harvest. How successful the project will be, time will tell.

About the author

Tim Sandle

Dr. Tim Sandle is a chartered biologist and holds a first class honours degree in Applied Biology; a Masters degree in education; and has a doctorate from Keele University.