For salmon in a recirculating aquaculture system (RAS), existing lighting conditions appear to be safe in terms of growth and mortality rates, according to the Norwegian research institute Nofima.
“However, we still know little about how the light affects salmon physiology and how they cope with the change in lighting condition after transfer to sea water,” said Jelena Kolarevic, Nofima senior scientist and project leader for CtrlAQUA’s research into light.
There is little existing research on what the optimum light intensity and quality in RAS should be, Nofima noted in an announcement, but white light-emitting diode (LED) lighting has become widespread in closed containment systems on land.
Very often, RAS is managed without in-loop disinfection, which means that more particles and organic substances are present in the water, preventing the light from penetrating the water column, Nofima said.
In sea-based net pen systems, daylight and clearer water represent the natural conditions where blue light penetrates the deepest, while red light and yellow light are more common in recirculated water due to the accumulation of substances like humic and fulvic acids, the institute explained. The insights from net pen farming are, therefore, not directly applicable for the conditions in RAS.
The CtrlAQUA scientists have looked into how the use of white and full-spectrum LED lighting affects salmon post-smolt in RAS and how the water quality affects light penetration, Nofima said. Light is traditionally used in salmon farming to regulate the timing for smoltification.
Based on experience from commercial RAS facilities, the scientists selected two light intensities -- 0.25 and 1.9 µmol/sq. m per second -- and two light qualities: white LED and full-spectrum LED. Post-smolts — i.e., salmon that have passed the smolt stage — were illuminated for 90 days, after which the scientists measured the water quality and salmon growth and mortality, Nofima said.
The results showed that a light intensity higher than 0.25 μmol/sq. m per second does not affect fish growth and survival in the RAS facility.
The industry is looking into the minimum light intensity required for optimum growing conditions in order to cut costs, Nofima said. However, challenges still exist, such as understanding the effect of light intensity below 0.25 µmol/sq. m per second.
“In the current large tanks with a depth of up to 5 m, it will be difficult for the fish farmer to be able to distribute the light evenly without major investments. It’s a challenge the industry has begun to look into,” Kolarevic said.
CtrlAQUA is a center for research-driven innovation that is developing technological and biological innovations that will make closed-containment aquaculture systems a reliable and economically viable technology in aquaculture. Nofima is the host institution, and there are six research partners from Norway, Sweden and the U.S. as well as 14 industry partners. CtrlAQUA is co-financed by the Research Council of Norway and its partners.