Trials in CtrlAQUA showed that both large and small smolt tolerated the transition to seawater. 93% of the salmon transferred to the sea survived. Photo: Terje Aamodt © Nofima

Project Year 2018

Biggest is not always best

 Production biology  

It seems that the largest smolt do not always perform best in the sea. New research shows that there is still more to learn about salmon.

Researchers in the CtrlAQUA innovation programme are working on the basis of the hypothesis that more time spent in recirculation facilities (RAS) on land will improve the fish’s growth and welfare in the sea.

However, RAS represent a new, constructed environment for salmon, where previous knowledge does not always apply. Results from a trial where salmon of different sizes were transferred from RAS to the sea show that the biggest fish not necessarily perform best.

“The question is whether it is most important that the time the salmon spend in the sea is minimized, or whether the overall production is as efficient as possible,” says project manager, Trine Ytrestøyl.

Lighting, brackish water and different sizes

Several production regimes have been tested using varying light-regimes, fresh water, brackish water and different sizes on transfer to the sea.

The fish with the best growth throughout life were the ones transferred to the sea at 100 grams after undergoing traditional smoltification with lighting control. The fish that
were 600 grams at the time of transfer had the poorest growth.

Perhaps the most surprising finding was that all the fish tolerated the transition to seawater,. The survival rate was not affected by light-regime or salinity in RAS, and a total of 93% of the salmon survived.

Several good production regimes

“It seems that salmon are quite flexible in terms of transfer to seawater, and that when they reach a certain size, they can develop salt water tolerance without lighting control. This paves the way for several different production strategies and greater flexibility,” says Ytrestøyl.

The scientist emphasizes that it may nevertheless be an advantage to reduce the time the salmon spend in the sea, in order to reduce the risk of escape and sea lice.

This illustrates that there are still unanswered questions with regard to how large postsmolt should be produced, and how the season and size at the time of transfer affects performance in the sea phase. Research will continue on these issues in CtrlAQUA.

The Research has been done in the BENCHMARK project in CtrlAQUA – Centre for Research-based Innovation (

Research partners and industrial partners in CtrlAQUA

The Research Council of Norway (NFR), The Norwegian Seafood Research Fund - FHF and partners

More useful research results