'We must spread the light evenly, that is the most important thing'

“I've talked a lot about wavelengths and stuff. What I think is the most important thing when choosing light for fish is the dispersion.”

So said Ole Gabriel Kverneland, chief executive of Laksesystemer AS (Salmon Systems), during the Future Smolt 2026 conference at Sunndalsøra in Norway this week.

In his lecture “From light to photobiomodulation”, he discussed how light can be actively used to influence biological processes in fish. But despite the many possibilities he sees in different wavelengths, there was one message in particular he wanted the participants to take away.

“Make sure that when we plan facilities, we spread the light as evenly as possible, so that there are no areas with shadow zones which the fish seek out and try to hide in, and that you do not have zones where there is too much light.”

He believes that consistent access to light should be a fundamental principle in the design of hatchery facilities.

“Uniformity, evenness in light availability to the fish, is the most important thing.”

Light and feeding must be distributed evenly

Kverneland also showed images illustrating the difference between uneven and even distribution of light and feed in a trough.

“See what it looks like if you distribute light and feed unevenly, and what it looks like if you succeed in spreading these inputs so that the fish have access on equal terms throughout the tank.”

His point was that lighting is not just about how much light is added to a tank, or what type of lamp is used, but also about how the light is actually made available to the fish.

Is light just light?

Kverneland began the presentation by challenging the traditional way of thinking about light in fish farms.

“I want to challenge myself a bit and try to get a professional curiosity around the topic: Is light just light?”

He explained the concept of photobiomodulation as the use of light energy to achieve a biological effect.

“We need to see what the biological result we want to achieve is.”

What do the fish perceive?

According to Kverneland, one of the challenges is that light is often described with units of measurement that are based on human vision, and not necessarily on how other organisms perceive or are affected by light.

“Perhaps the main problem is that we tend to talk about what people themselves see.”

He referred, among other things, to experiences from agriculture, where different wavelengths are actively used in both plant production and livestock farming.

In greenhouses, for example, red and blue light are used to utilise the parts of the light spectrum that plants absorb best.

“Then they save the energy that this plant doesn’t need,” he explained.

Kverneland also pointed out how the poultry industry uses its own methods of measuring light, adapted to how chickens perceive it.

Can affect circadian rhythm and smoltification

When it comes to fish, Kverneland particularly highlighted the importance of blue light.

“One of the things we know today is that blue light has a very effective regulation of the fish’s circadian rhythm. It effectively inhibits melatonin and is a clear signal for the fish.”

He pointed out that the circadian rhythm is important for central biological processes, including smoltification and sexual maturation.

“We know that blue light, the blue part of the spectrum, is very activating and gives the fish clear signals about their circadian rhythm.”

At the same time, he believes that it is necessary to take a broader look at which parts of the light spectrum may be relevant.

“These are things that are incredibly important for us to take into account when we move the fish from their natural environment outside and into a closed environment where we decide what light they will receive.”

He also pointed to research investigating whether UV light can contribute to increased production of vitamin D in fish.

Green light can have interesting effects

Another part of the presentation was about the possible use of green light.

Kverneland referred to research on fish species other than salmon, particularly flatfish, where green light has been investigated with regard to, among other things, stress, immune defence, growth, and wound healing.

“There is some evidence that green light has a stress-reducing effect. It has been shown that fish have better immunity and better growth with the use of green light.”

He also highlighted studies that, he says, show differences in wound healing between fish exposed to green light and fish exposed to white or blue light.

At the same time, he emphasised that such results cannot simply be transferred to all fish production.

“Now, I'm not saying that the answer is that we should use green light so the fish will grow better.”

The point was rather that choosing wavelengths can become a more active tool in production.

“We can use active selection of wavelength, active selection of light that stimulates and provides energy to various biological processes in the fish, to steer towards the results we want.”

Also sees opportunities for energy savings

Kverneland believes that more targeted use of light can also contribute to lower energy consumption in land-based facilities.

Among other things, he highlighted that red light is largely absorbed by the water and thus adds heat to the system.

“This again means, in RAS systems, that you have more heat that you have to remove with cooling in the system.”

By choosing light with a spectral composition that produces desired biological effects to a greater extent, he believes it may be possible to reduce energy use.

“Shifting the light into a spectral range that has the greatest possible biological effect can provide quite significant energy savings in this type of facility.”

Kverneland said that Salmon Systems has developed different categories of lighting that are intended to provide different biological effects, including lamps with a greater proportion of blue or green light.

Significant difference in mortality

Towards the end of the presentation, Kverneland pointed to an example from a customer who had tested one of the company’s lamps.

According to him, there was initially a very high average mortality rate of 43% in the production system. But in a group where the customer had tested a lamp that Laksesystemer believes can have a stress-reducing effect, the mortality rate was 15%.

Kverneland did not provide further details about the experimental design or other factors that may have influenced the results, so the figures alone cannot determine that it was the lighting that caused the difference in mortality.

He nevertheless believes that the example illustrated the potential for further development.

“It is quite clear that there are opportunities to improve conditions in the industry.”

Kverneland also emphasised the need for more research into how different wavelengths actually affect fish.

“It is now up to the researchers here to prove wavelengths and effects on the fish.”