SalMar’s “Marine Donut” closed-containment aquaculture system heads to sea

Frøya Municipality, Norway-based SalMar has taken delivery of the “Marine Donut,” a massive plastic structure the company plans to use as an enclosed aquaculture system for farming salmon. 

The donut is, as its name implies, a 600-metric-ton donut-shaped, closed-containment fish farm built by Stathelle, Norway aquaculture technoloy firm Bluegreen. The enclosed farm, which Bluegreen said is the largest thermoplastics structure in the world, is meant to prevent salmon escapes; minimize risks of disease, algae, and sea lice; and reduce the use of antibiotics and other medicines. 

The donut consists of a torus-shaped closed unit made of high-density polyethylene that serves as a barrier against the surrounding ocean environment. Floating pipes serve as ballast to keep the system upright and as systems to allow the cage to be raised out of the water or submerged when needed. 

The interior uses a flow system that can be adjusted to exercise the fish – Bluegreen said that it mimics the environment of a river. The design also provides “good fish density” throughout the entire facility, the company said.

Bluegreen CEO Nils-Johan Tufte said while initial production costs are higher for the donut than for net-pens, those costs are offset by its farming efficiency.

"The production cost per kilo will be competitive. It eliminates the need for delousing treatments, has twice the density, shorter downtime, lower mortality, and better feed-conversion ratio,” Tufte said in a release. “It will be exciting to verify the hypotheses."

Tufte said the idea for the salmon farming donut came to him in 2015 as a method to sustainably farm salmon with minimal environmental impact. Norwegian salmon farmer Mowi initially picked up on the idea and other composite-based, closed-containment aquaculture units – such as its “Egg” salmon farm – and was granted two development licenses by the Norwegian Directorate of Facilities for the Marine Donut concept. Mowi ultimately scrapped the ideas, selling them for NOK 253 million (USD 25 million, EUR 24 million) after deciding they were too costly. Bluegreen purchased the Egg-concept farming permits from Mowi, and SalMar commissioned the project from Bluegreen in September 2022. 

“SalMar is innovative and ambitious. They are not afraid to explore new technology that solves the challenges facing the industry,” Tufte said. “We are impressed by their investment in off-shore farming, and we hope that Marine Donut can play a role in this.”

SalMar COO Farming Roger Bekken said the new farm continues SalMar’s legacy of innovation.

“Marine Donut is an exciting concept and we look forward to developing the concept further together with the supplier,” Bekken said at the time the company commissioned the new facility.

Now, the 600-MT Marine Donut has made the 510-nautical-mile journey from Bamble, Norway, to the Romsdal Fjord, where SalMar will fill it with 200,000 salmon weighing 2.5 kilograms each. The fish will then swim in the donut’s 22,000-cubic-meter interior until they reach a 5.5-kilogram harvest size.

"Now the real fun begins," Tufte said. "This is where we verify our hypotheses that Marine Donut promotes fish health, delivers premium fish quality, and ensures profitability for the fish farmer."  

Photo courtesy of Bluegreen Group/Droneinfo