"Fish farmers tell us that they want a ban on the use of certain species. They're also very critical of wild-caught cleaner fish being transported," says researcher Kristine Størkersen. She is one of the scientists who have been helping the Norwegian Food Safety Authority gain an overview of the situation.

The term "cleaner fish" is used to describe the small fish species that will eat salmon lice as snacks.

Letting cleaner fish cohabit with salmon seems like a good idea at first glance. Salmon lice are a well-known problem, both for wild salmon and farmed salmon, and chemical delousing methods are harmful to nature. Keeping salmon lice under control has become a significant yardstick by which Norwegian salmon farming success is measured.

So it is no wonder that the use of cleaner fish has picked up, and even led to the separate side industry of farm raising cleaner fish.

Gradually, however, awareness is growing that this solution has its dark side. Many cleaner fish species have trouble adapting to life in the sea cages, and are not doing well.