Mowi Scotland calls a halt to lumpfish production and use

Salmon farmer Mowi Scotland has stopped using lumpfish as a form of biological lice control and discontinued production of lumpfish at its Ocean Matters facility in Anglesey, Wales.

News of Mowi’s decision to stop using lumpfish was first published by investigative news website The Ferret last week. The website reported that the development followed its report in June of the deaths of 135,000 lumpfish at a Mowi farm in the Highlands.

Mowi told The Ferret it has invested in new technology that is safer for fish, and that sea lice levels have reached their “lowest levels in more than a decade”.

The fish farmer has in the past used two types of fish – lumpfish (Cyclopterus lumpus) and ballan wrasse (Labrus bergylta) – as “cleaner fish” which share a pen with farmed salmon and eat the parasitic sea lice that attach to the salmon. Ballan wrasse are generally considered more effective at removing sea lice than lumpfish, but take longer to grow.

Ballan wrasse

Both cleaner fish species were farmed at Ocean Matters, and Mowi Scotland – the UK’s biggest fish farmer – will continue to produce and use ballan wrasse to supplement other sea lice control methods which include freshwater treatment in wellboats.

“Mowi is constantly reviewing all options available with regard to protecting the fish in our care from sea lice, including all cleaner fish. With this in mind, we have taken the decision to stop using lumpfish at this time,” Mowi Scotland said in a statement. 

“Cleaner fish continue to be one method available to us in a suite of methods which include freshwater treatment in wellboats. Mowi has also made major investments in FLS mechanical delousing to gently remove sea lice after freshwater baths.”

Enhanced capacity

Mowi Scotland's capacity to treat its fish for sea lice was enhanced in 2023 and 2024 by the delivery of two newbuild wellboats - the Inter Atlantic and the Inter Scotia - contracted from Intership. Both vessels have freshwater baths, while the Inter Atlantic has an FLS Caligus R500 delousing system and the Inter Scotia has the very latest FLS Caligus R600 system. 

Fish pumped aboard the vessels spend several hours in freshwater, which causes some lice to drop off and other to be weakened, then the FLS system gently flushes fish with seawater to remove the remaining lice. 

The combination of a freshwater bath and flushing fish through the FLS system has the advantage of tackling sea lice and gill infections in the same operation.