It has long proved difficult to find other uses for lumpfish once it has finished its mission as a lice eater in fish farms.

Now it turns out that the small cleaner fish might be well suited as feed for small king crabs.

“The idea behind the research project Kongemat (Food fit for kings) was to find a sustainable way to utilize lumpfish,” says Nofima Scientist and Project Manager Birthe Vang.

Cleaner fish in fish farms stop eating salmon lice when they reach sexual maturity. It is therefore important to find alternative uses for this valuable resource so that it can be utilized in a sustainable manner. Currently, the aquaculture industry often has to pay to get rid of excess cleaner fish—not an ideal situation from both an economic and animal welfare perspective.

“So far, millions of cleaner fish have been used in fish farms to deal with salmon lice. Now it looks like lumpfish are about to be phased out as cleaner fish. Wild lumpfish are still being fished, however, where mainly the roe from female fish is utilized, so there is still a lot of lumpfish available for alternative uses,” says Birthe Vang.

Suitable As Bait in Crab Fishing

Several attempts have been made to find new, effective ways to utilize lumpfish after they have stopped eating lice, or the roe has been collected, but none of them have been successful.

A project led by Nofima looked into the potential use of lumpfish for human consumption in South Korea.

“The results from the market test in South Korea show that it can be challenging to sell whole cleaner fish for human consumption,” says Researcher Gøril Voldnes.

“They did not like the appearance of the fish at all. They thought it was rather scary looking and very unappetizing. In addition, the respondents said that the fish didn’t have much taste, the texture was too soft, there was very little meat, and their lice-eating history was simply unpleasant,” says Birthe Vang.

Nofima scientists then attempted to test whether lumpfish could be a suitable raw material for extracting the popular and important protein collagen.

“But no, it turns out it does not actually contain a lot of collagen,” Vang states.

However, lumpfish have proved suitable as bait in crab fishing, so the researchers asked themselves: Can it be used for feeding small king crabs until they reach commercial size?

Increased Appetite and Feed Intake

(Image credit: Anne-May Johansen, Nofima)

Nofima already has an ongoing project titled Helt konge (Crab is King) which focuses on precisely how to rear small crabs from 250 grams up to a marketable size of around 1.3 kilos and up. Nofima’s feed experts have already developed a suitable feed.

Using that as a basis, Birthe Vang and her colleagues in the departments of marine biotechnology, seafood industry and production biology at Nofima got to work.

“We wanted to test whether whole or processed lumpfish that have been used as cleaner fish can boost the appetite and feed intake in small king crabs, and thereby boost the meat content and value of adult king crabs,” says Birthe Vang.

Developing a Taste for Feed Coated with Lumpfish Concentrate

24 king crabs at the Aquaculture Research Station in Kårvika outside Tromsø were included in the 12-week trial:

• 6 received king crab feed developed in the Helt konge project
• 6 received coated feed—that is, the original king crab feed coated with a “syrup” of concentrated, water-soluble lumpfish proteins, developed by using enzymatic hydrolysis.
• 6 received 50/50 king crab feed and pure lumpfish
• 6 received only lumpfish

Work on analyzing the results is now in full swing. The researchers theorized that dry feed coated in lumpfish concentrate would be more tempting for the crabs than regular feed. They believed that the water-soluble proteins from the lumpfish concentrate would act as a flavor enhancer to make the feed more appealing and whet the crabs’ appetite. So far, this seems to be the case.

“So far, we can conclude that the crabs ate much more of the king crab feed throughout the experiment. Halfway through the experiment, they also started developing a taste for pure lumpfish. This could indicate that the crabs need an adaptation period to get used to new feed,” says Birthe Vang

Contribution to a Circular Bioeconomy and Increased Utilization of Raw Materials

The dry pellets on the left are the original feed developed by Nofima for the Helt konge project, which involves rearing small king crabs to commercial size. The shinier pellets to the right are the same feed but coated with a ‘syrup’ made from lumpfish with the intention to make the feed more appetizing. (Image credit: Birthe Vang, Nofima)

15 wild-caught crabs from outside Honningsvåg are also included in the project to measure meat content and check the crabs’ intestines for what they have eaten. These crabs will be compared with the crabs in the current project, which have been exposed to different feed regimes, to be able to determine which type of feed will provide the maximum meat content in the crabs’ legs.

“Based on the results from the initial trials at the Aquaculture Research Station, the three best feed regimes will be piloted at Storbukt Fiskeindustri in Honningsvåg. We will be feeding 300 small crabs weighing approximately one kilogram over a three-month period,” says the project manager.

Of all the seafood Norway exports, the king crab achieves the highest price per kilo.

“If we succeed in developing this feed, it will contribute to the development of a circular bioeconomy and increased utilization of raw materials. It will also help to increase value creation in the seafood industry and facilitate local jobs if the commitment to live storage and feeding of king crab succeeds,” says Birthe Vang.

The Helt konge project is funded by MABIT, an industry-oriented R&D program in marine biotechnology in Northern Norway.