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Ballan wrasse are fussy eaters but good lice removers from the off. Photo: Nofima
Ballan wrasse are fussy eaters but good lice removers from the off. Photo: Nofima

Researchers in Norway will develop a four-year project intended to acquire the necessary knowledge for the correct feed and the nutrition needed for cleaner fish to survive and become more efficient salmon lice-eaters.

The scientists involved in the project, called ‘CleanFeed’, claim that lice do not contribute enough nutrition to support lumpfish and ballan wrasse,the two cleaner fish used in salmon cages.

The industry expectation is for both species to be robust, have low mortality and a solid health and nutritional status in order to thrive and do their job as lice eaters.

“In this project, we will find the optimal composition of feed for the sizes of lumpfish and ballan wrasse concerned. Because the two species are so different to begin with, it is necessary to develop feed that is suitable for each individual species,” points out Øystein Sæle of the National Institute of Nutrition and Seafood Research (NIFES).

Ingrid Lein: Good nutrition is a prerequisite for efficient cleaner fish. Photo: Nofima.
Ingrid Lein: Good nutrition is a prerequisite for efficient cleaner fish. Photo: Nofima.

These scientists, led by Ingrid Lein of Nofima, explained that experience from cultivated lumpfish shows that they can often develop grey cataracts and that good sight is especially important to the cleaner fish so they are able to graze efficiently on the lice attached to the salmon.

Researchers will investigate whether there is a connection between feed and the development of cataracts. A probable candidate is the amino acid histidine, which is important for osmoregulation and other processes in the lens.

Good intestinal function is also important for good health and well-being. “The intestines are actually a very important part of the immune system, and function as a barrier between the fish’s insides and possible outer impacts from feed and water,” explains Åshild Krogdahl of the Norwegian University Of Life Sciences (NMBU).

In the project, the NMBU School of Veterinary Science will investigate how changes in the composition of feed can affect intestinal function and health.

Fussy eaters

These researchers recognise that knowledge about the composition of nutrients is the starting point for making feed but it is necessary to know what raw materials should be used. Ballan wrasse are fussy eaters, and currently feed is made using high quality ingredients that are really made for human use, such as shrimp and krill oil.

“We will test more relevant raw ingredients for ballan wrasse; aquatic, vegetable and animal raw ingredients, and preferably downstream processed residues. It is important to find raw ingredients that can be combined in the correct mix, and that result in good survival and growth, and good well-being and health for the fish,” says Katerina Kousoulaki of Nofima.

Lumpfish, on the other hand, eat most of what they are given, and can grow remarkably fast, from the fry stage and onwards. This is not necessarily a good thing, as rapid growth requires more feed, and a lack of certain nutrients can more easily occur.

High mortality

In addition, high mortality rates for cleaner fish in the cages are often reported, which is a problem that scientists participating in CleanFeed hope to solve.

“The objective is for cleaner fish, preferably a combination of lumpfish and ballan wrasse, to be in the cage with the salmon throughout an entire production cycle. One of the prerequisites for this is without doubt good nutrition for the cleaner fish. We are looking forward to obtaining results in this project over the next four years,” Lein concluded.

The project is funded by the Norwegian Seafood Research Fund (FHF) and is the result of the collaboration of NIFES, the NMBU School of Veterinary Science and NTNU Ålesund.