Why cleaner fish?
The salmon louse is the most common parasite on farmed salmon, and one of the biggest challenges for the aquaculture industry. Cleaner fish, which from nature's perspective are designed to feed on such parasites, are used in the cages to feed on lice from farmed fish.
Under the right conditions, this represents an effective form of biological delousing that can prevent chemicals entering the environment and saves a lot of money for the farmer.
Lice can be controlled with a combination of different measures, without the use of chemicals. This can be by using cleaner fish, mechanical removal, breeding, vaccines and feed.
Have been shown to be effective in many places. Both wild-caught and farmed cleaner fish are used extensively today. There is apparently a correlation between the robustness of the cleaner fish and its effectiveness in terms of feeding on lice.
Farmed fish can also be deloused using measures such as flushing, brushing, warm water, freshwater and lasers. The measures are based on newly developed technology which is driven by an innovative industry.
Research is being carried out on QTL spawn, which can improve the fishes' resistance to salmon lice. QTL spawn exists today with extra resistance to the IPN virus and PD.
Research is being carried out into vaccines that can provide immunity to salmon lice. This is probably a long way in the future.
Strengthening of the fishes' outer barriers by using feed with functional ingredients affects the composition and thickness of the mucus layer on the skin. The mucus layer can increase the fishes' general ability to resist and can reduce louse infestation by not allowing the salmon lice to attach themselves to the salmon. A thicker layer of mucus will also stand up better to mechanical damage.
Cleaner fish represent an effective biological method for the removal of lice. This means that delousing can potentially be carried out without the use of medications. It is not expected that resistance problems towards cleaner fish will develop, which would be the primary limiting factor for delousing with cleaner fish. In addition, the costs of using cleaner fish are much lower than for other methods. The cleaner fish itself can also be a valuable source of protein for the future.
Wrasse and lumpfish have complimentary characteristics.
- As cold-blooded creatures, wrasse are most effective at higher temperatures.
- They are less effective in the winter when temperatures are lower and if it gets cold enough, they can assume a trance-like state.
- Lumpfish are active and effective at lower temperatures, but find it difficult to deal with temperatures above 15°C.
Less hydrogen peroxide
- Cleaner fish can limit the use of the delousing agent hydrogen peroxide which is widely used in the aquaculture industry.
- Since the louse is a crustacean, it is not unlikely that other crustaceans may also be affected by this agent.
- In one trial, the common species of purse shrimp and beach shrimp were exposed to hydrogen peroxide.
- For a short period, both species tolerated being exposed to concentrations corresponding to a treatment solution.
There is currently no established way to reuse lumpfish and wrasse when they have finished being used to feed on lice in the cages. Work is being carried out to find different areas of use, from using them as a raw material in fish and animal feed to developing possibilities as fish for human consumption.
Benefits for farmers
Cleaner fish are cheaper than chemical treatment of salmon lice, but cannot on their own be the only solution to control the number of lice. They must be used in conjunction with other methods, such as lice skirts and lice flushing. One of the reasons for this is that cleaner fish are not equally active the whole year round, and cannot always manage to remove all the lice.
Farmers of lumpfish are optimistic, and believe that they can solve a large part of the louse problem. The financial benefit and the health of the cleaner fish and its ability to survive are clearly connected. The Norwegian Veterinary Institute has mapped out mortality of and cause of death in cleaner fish.
The report shows that some types of farmed and vaccinated cleaner fish are better equipped to withstand sickness and death. The species that are included in the project are the lumpfish and all the common species of wrasse; goldsinny, ballan wrasse, corkwing, small-mouthed wrasse and cuckoo wrasse. Almost a million cleaner fish were monitored at 17 different sea locations and one hatchery.
Cleaner fish that are farmed and provided with optimum feed are more robust and more resistant. Characteristics that it also appears possible to strengthen with proper tending and feeding while in the cage.