Algae-based feed shown to deter salmon lice

For more than a year, researchers at UiT – Norway’s Arctic University and Nofima in Tromsø have been researching whether selected Arctic microalgae can be a deterrent to salmon lice.  

On its website, UiT states that the microalgae used are silica algae produced using waste gases from a smelting plant in northern Norway that produces ferrosilicon, an important raw material in the steel industry. As part of the process the microalgae remove carbon dioxide and nitrogen oxides that would otherwise have been emitted.

Omega-3 ratio

The project is funded by fisheries and aquaculture funding body FHF and regional county funds and its focus has included whether the ratio of omega-3 to omega-6 in feed may have some bearing on how attractive salmon are to salmon lice. The researchers assumed that a reduced content of omega-3 in feed has led to salmon secreting fewer oxylipins in the skin (see fact box).

Researchers also had evidence that oxylipins from algae can deter invertebrates, including salmon lice, which are copepods. They wanted to test whether it was possible to reduce the onset of salmon lice by, among other things, using algae in feed.

Significant reductions

“We have carried out several experiments where we have included algae, copepod-derived oil and regular fish oil in feed, and compared this with normal vegetable feed,” Ragnhild Dragøy Whitaker, head of research at Nofima, told Fish Farming Expert’s Norwegian sister site, Kyst.no.

After this, the researchers at UiT and Nofima looked at lice numbers.

Whitaker said that they observed significant reductions in lice infestation especially when using feed with added algae and some reduction with feed with added calanus, a marine copepod.

Several parameters

“In addition, we are investigating several parameters in the project, including skin, growth and fat content in the fish,” said Whitaker, who said that the project is not completely finished and that there are still more analyses remaining.

“Among other things, we will look at oxylipin levels in the skin and what the reason is for the salmon to have fewer salmon lice. So far, we have just been confirmed it to be the way it is,” the researcher pointed out.

Another important aspect of the project is finding new sources of marine oils and proteins that can be used in fish feed.

A win-win

“Microalgae can then be a win-win because they consume CO₂ exhaust gases from heavy industry (the Finnfjord smelting plant), and because this can be scaled up to full industrial size,” Whitaker explained.

Although microalgae can be an alternative source of marine oils and proteins, there is more that remains to be done before using microalgae.

“The question is how much volume we can produce, and how much one can include in the feed while maintaining good growth.” This is what researchers at Nofima are watching, she said.

It can also be difficult to process new biomass such as microalgae, for both feed and other products.

“If you get these things in place, one will, as mentioned, get a win-win situation. This is a super story,” she concluded.

Oxylipins and lice

• Oxylipins are derivatives of fatty acids that contain oxygen and participate in organisms’ developmental processes.
• Oxylipins are found in all aerobic organisms, fungi, algae, mosses, plants, animals and blue-green bacteria. Prostaglandin is a well-known oxylipin, which is central to inflammatory processes.
• In the trial discussed here, the hypothesis is that there is a link between lice attraction and altered (reduced) ratios of omega-3 versus omega-6 fatty acids in feed.
• Omega-3 is a precursor to oxylipins, and reducing them in the feed leads to reduced secretion of oxylipins in fish skin.
• Oxylipins from algae have also been documented to scare away invertebrates, including copepods. Salmon lice are copepods and it is possible that salmon lice onset can be reduced by active use of oxylipins in salmon farming, as well as a higher omega-3 / omega-6 ratio in the fish feed.