99% smolt survival in closed pens

In seven years, the Norwegian fish farmer Hardingsmolt has sent more than 11 million post-smolts through its floating closed containment pens into the sea, and after the introduction of a new winter sore vaccine, the last six million have had a survival rate of 99%.

This was stated by general manager Frode Sandven during the seminar "From decline to recovery" about closed post-smolt production in the sea, organised by Ocean Tales during the HavExpo trade show near Bergen in Norway this week.

The company received a development permit together with Merdslippen seven years ago, and has since produced post smolt in closed cages at sea. 

Today, Hardingsmolt has 24,000 cubic metres of closed volume distributed across four GreenBag cages, and has also ordered two new GreenBags and a Heimdall cage from ScaleAQ. This will increase capacity by a further 32,000 cubic metres.

A different path

"The traditional way in hatchery production is to have larger freshwater tanks that they can run the growth in for a long time, and then smoltify the fish before they go out to sea in an open cage," said Sandven.

Hardingsmolt has chosen a different model. After three months in the hatchery, three months of starter feeding and three months of growth in freshwater, the fish are moved to brackish water tanks.

"For our part, we have a brackish water department, and it is part of the key to our ability to make our post-smolt production so efficient, as it gives us great flexibility."

The fish then spend another three months in brackish water at the hatchery in Tørvikbygd before being stocked into the closed cages in the sea on Koløy near Fitjar, south of Bergen.

Stocks fish from 100 grams

At the Koløy location, the strategy varies depending on the size customers want.

"On Koløy, some of the fish are released into the closed cages when they weigh 100 grams and swim there until they reach one kilogram and are sent out. Other groups are released at higher weights and will grow even larger before being sent to customers."

Today, the company takes fish from around 100 grams to almost 2kg in the closed cages. The production time in the sea varies from one to six months, but in the future, Hardingsmolt will also try to leave 100,000 fish to grow to food fish size to test the concept further.

At the same time, Sandven emphasised that high utilisation rates are crucial for the economy of closed systems.

"When you make such large investments as there are with closed facilities, there must be fish in them as much of the time as possible."

According to Sandven, with the exception of fallow periods, the closed cages have constantly had fish in them  since the first two GreenBags were put in place in August 2019.

24-hour crew on the raft

The facility is located around 600 metres from shore and is equipped with its own oxygen production and a feed silo on the raft.

"On the raft we have a barracks, so we have employees who live on the raft and work shifts for a week at a time. We also have a feed silo and oxygen production out on the facility, because it is located several hundred metres from shore."

Sandven said that the company is still working on optimising oxygenation, but believes that the cage concept itself has worked well and been gentle on the fish.

"It's about creating an ecosystem that we have control over, in the best possible and affordable way."

He also emphasised that different technologies and concepts can work well if they are adapted to the location.

Winter wounds were the big challenge

The biggest biological challenge in the start-up phase was winter wounds.

"We struggled with winter sores during the first releases. There wasn't much infection between the bags, but once an infection got into a cage, it was difficult to get rid of."

The solution came when the company began vaccinating with the new winter sore vaccine.

"There has been a huge improvement after we started vaccinating with AlphaJect Moritella. After that, we have had 99% survival in the closed cages."

According to Sandven, the company has only registered one louse in the 11 million fish that have passed through Koløy. It has thus avoided treatments and the strain that comes with delousing for the welfare of the salmon.

Critical of the regulations

Despite good results, Sandven is frustrated with the current regulations for closed facilities.

The smolt producer has had to go through several rounds to get its operating plans approved, and the company has also been hit by reductions in production allowances on two occasions, even without lice in the facility. Reductions are imposed under the traffic light system, and apply to every farm in a production area, regardless of individual performance.

"I wish we could define the goal a little more, and reward those who take action," said Sandven.

More cost-effective

Producing post-smolts at sea is more cost-effective than doing that part of the production on land, believes the Hardingsmolt manager.

At the same time, he said that operating closed facilities requires a high level of expertise and continuous monitoring.

"We haven't had any serious incidents, but things have happened to us like all farmers. It has gone very well, but I depend on having good people on site, who know what they are facing. It is a bit more complicated to run production in a closed environment than in a regular cage," Sandven said.