SalMar switching to post-smolt production in Marine Donut
Unit is being transitioned to commercial use following end of tests with large fish
The Marine Donut floating closed containment unit trialled by salmon farming giant SalMar for growing harvest-sized fish is being adapted to produce post-smolts, the unit’s developer Bluegreen announced today.
SalMar has been operating the facility under a Norwegian government "development licence", which gives a producer temporary extra biomass capacity to offset some of the costs of investing in a new production method.
But the Donut is now being transitioned to regular commercial operations, said Bluegreen, which added that experience gained from full-scale testing has provided valuable insights into biology, operations, and construction, and now forms the foundation for bringing the technology into standard production.
“The transition from a development licence to regular operations means that the facility must be adapted to its intended use. Post-smolt production has different requirements compared to grow-out, particularly in terms of number of individuals and fish size,” said Bluegreen chief technology officer Henrik Thorstensen.
The work includes new technical assessments and adjustments to fish barriers for post-smolt production, as smaller fish require stricter mesh sizes and enhanced barrier functionality.
Aiming for 1 million
“The next step will be finalising the conversion and submitting applications for exemptions to allow stocking of up to 1 million individuals,” Thorstensen said.
Bluegreen said the biological and technical foundations of Marine Donut had already been developed with high biomass density and stable operations in mind. The full-scale tests had demonstrated strong biological results, and these experiences were now actively being used to optimise the facility for post-smolt production.
SalMar plans to use Marine Donut for post-smolt production with spring stocking, before transferring the fish to open sea sites for final grow-out. The use of closed technology in this phase reduces exposure to external environmental factors and provides greater control during a critical stage of the production cycle.
The work now under way is about bringing the technology into standard operations and adapting it to new applications. This is an important step in the commercialisation of the solution
“Marine Donut has delivered very strong results during the development phase. The work now under way is about bringing the technology into standard operations and adapting it to new applications. This is an important step in the continued commercialisation of the solution,” said Thorstensen.
Two-month test
Earlier this month, the final assessment of the second production cycle in the Donut reported stable environmental conditions, good fish welfare and low mortality. Production cycle 2 ran from May 4 to July 6, 2025.
"After ten years of development, we are finally moving into a commercial product. The prototype we have run through the development concession has given us the answers we need to deliver Marine Donut 2.0 as an optimal end product," Bluegreen sales and marketing director Geir Andresen told Fish Farming Expert's Norwegian sister site, Kyst.no.
Water quality and environmental parameters were monitored continuously throughout the production cycle. Oxygen, temperature, salinity, pH, turbidity, CO2 and algae content were measured, in addition to weekly measurements of total gas and suspended solids.
Stable oxygen content
The measurements show that the water quality in Marine Donut has been good and stable throughout the period. The average oxygen level was 91.5%, and high feeding over extended periods did not have a negative impact on oxygen levels.
"We are very pleased that, with a very high fish density of up to 50 kilograms per cubic metre, we are able to maintain very good and stable water quality conditions in full-scale production with 1,000 tonnes of biomass," said Andresen.
