Atlantic salmon nutrition could have a local twist

Ragworm

This little creature can help the salmon farming industry overcome a major challenge by providing fish with locally sourced, sustainable food

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Haiqing Wang, SINTEF

Norwegian researchers have launched an offbeat idea: feeding ragworms with locally grown algae. The results were as valuable as the worms themselves – a high-quality, locally sourced, sustainable food for farmed salmon.

“Ragworms are an exciting new food raw material that can help reduce the industry’s reliance on imported materials, making Norwegian salmon a more environmentally friendly and sustainable product,” says researcher Andreas Hagemann. at SINTEF.

Seaweed is also a major resource and in recent years many companies have set up along the Norwegian coast to cultivate it. Researchers have now demonstrated that algae is ideal as food for ragworms, which in turn can be made into a high-quality food for farmed salmon.

Demand for more sustainable food alternatives

The algae-lice worm combination can also help solve a major problem. The salmon farming and animal feed sectors need new sustainable raw materials. It is vital that they become less dependent on soy protein and other less environmentally friendly raw materials that have to be transported long distances to supply Norwegian fish farms.

“Seaweed has high carbohydrate levels but is too low in fat and therefore cannot be fed directly to farmed salmon,” says Hagemann. “However, by first feeding the algae with the ragworms, we get a high-quality food, rich in omega-3s and with the right composition of other fatty acids and marine proteins. It is also a good way to enhance residual raw materials from seaweed production,” he says. The research is being carried out as part of a project called POLYKELPwhich is coordinated by SINTEF Ocean.

The central idea

Although seaweed is not suitable for feeding salmon directly, it has many valuable properties that open the door to multiple uses. Seaweed intended for human consumption is generally harvested in the spring. As the plants grow larger during the summer months, they often become clogged, making them less attractive as food for humans.

However, plants are at their peak during the summer months, so farmers can harvest larger volumes. Additionally, seaweed scraps can be used as food. Thus, there is no shortage of available seaweed raw materials that can be used for a wide variety of useful applications.

person holding a kelp blade
Farmed algae

Seaweed is a very useful raw material. Large-scale cultivation can remove CO2 from the atmosphere, and they can be used both as food and as a soil amendment in agriculture. They can also play an important role as a sustainable raw material for the local feed supply for farmed salmon.
© Ingar Storfjell

This led to the original idea of ​​first feeding the ragworms algae, then feeding the worms the salmon.

Omnivorous lice worms?

Although ragworms (diversicolor hedist) are primarily omnivorous, the researchers were very interested to see how well they would accept being fed algae.

“They will eat just about anything, but this was the first time we had tried to feed them purely vegetable matter,” says Hagemann. “Part of our goal was also to see if ragworms can survive on algae alone, and find out how that influences their growth rates and nutrient values,” he says.

They noted that seaweed is too low in fat to be used as a salmon feed, but becomes ideal when refined or bioconverted by the extra step of being eaten by ragworms.

“Our results show that algae provide ragworms with an excellent variety of fatty acids and that the quality of the worms’ diet is greatly improved by being fed the low-fat raw material,” says Hagemann.

Get inspired by silage bales

“Because the algae season is so short, it is important to preserve the plants after they are harvested,” says Hagemann. “Acid preservation, which is the method used when we store silage in bales, is a simple and inexpensive approach that works for algae as well. For this reason, our goal was to compare the feeding of the worms with algae stored in this way with plants that had been kept in frozen storage and then thawed,” explains Hagemann.

So the researchers served both acid-preserved seaweed and frozen seaweed to the ragworms every day for nearly two months.

“The ragworms fed well on both types, and the preservation methods had no effect on the later nutritional value of the worms in terms of fatty acid content,” says Hagemann.

Andreas Hagemann and Andrea Rodriguez
Andreas Hagemann and Andrea Rodriguez

Principal investigator Andreas Hagemann and PhD student Andrea Rodriguez study a ragworm following an experiment

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SINTEF

Optimizing Ragworm Diet

These experiences should be seen as the beginning of a longer process. Researchers don’t yet know if seaweed alone is an ideal food for ragworms, but they’ve had positive results and are now working to optimize ragworm diets.

“In the future, we will investigate how algae can be transformed into an even better food for ragworms,” ​​says Hagemann. “We will also see if the nutritional profile of the worms can be improved, perhaps by combining the algae with other types of residual raw materials,” he says.

A major local resource

“These excellent test results are very good news,” says SINTEF researcher Jorunn Skjermo, who is keen to point out that access to cultured algae is almost unlimited.

farmed kelp
Breeding seaweed line

Seaweed farming is a growing industry and there are currently around 20 companies growing seaweed in Norway.

“Since seaweed is grown in floating marine facilities all along the Norwegian coast, there are no limits to the availability of this raw material, as there is with natural seaweed,” says Skjermo. Such facilities can be located in areas without much other activity, provided the space made available for the infrastructure is large enough to meet production needs,” she says.

Seaweed farming is a growing industry and there are currently around 20 companies growing seaweed in Norway. Globally, it’s a gigantic industry, producing over 300 million tons every year.

“In Norway, we have established the natural prerequisites for the production of seaweed and lice worms,” ​​says Skjermo. “Because seaweed farming is considered a sustainable method of producing raw materials, there is a lot going on in the sector at the moment, both in Norway and abroad. The sector is growing and interest is increasing. More material is produced locally and multiple uses are identified,” she says.

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