Land-based Fish Farming - is the Fish Better off?

Fish that are farmed on land are considered more sustainable, as it has minimal impact on the environment. But is fish raised on land better off?

For decades fish, and salmon in particular, have mainly been raised in large net pens in the sea. But now billions are being invested to start land-based salmon farms around Sweden. The fish are then farmed in basins or tanks, where the water circulates in a closed system, known as recirculating aquaculture systems (RAS).

Researcher Kristina Snuttan Sundell, professor of zoology at the University of Gothenburg, has done research in this area. She believes that land-based farms can be better for the fish.

– Good quality of the water is important for fish welfare. Fish are dependent on the composition of the water, as there is a constant exchange of substances between the fish and its surrounding water. Land-based fish farms provide a good opportunity to control the fish’s living environment. 

Major consequences for fish in sea-based facilities

Fish that are farmed in the sea can have major consequences for the environment, as well as the fish itself. Horrifying pictures show salmon swimming in net pens with ulcers and skin lesions because of the huge problem of salmon lice. The media sound the alarm about sick and deformed salmon escaping and infecting wild stocks. Reports indicate that sea-based facilities contribute to the nutrients increasing in the oceans, which can lead to eutrophication and degradation of the marine environment.

With land-based RAS-systems, some of the consequences can be prevented – at least in theory. The closed water systems make it much more difficult for fish to escape into the sea, reducing the risk of disease and parasites spreading to wild stocks. They also reduce the number of substances that can enter the sea and contribute to eutrophication, such as nutrients (nitrogen and phosphorus in particular) and organic matter from fish feces and feed residues.

A controlled environment and water quality

According to Kristina Sundell, one advantage of land-based fish farming is the ability to quickly correct water quality if necessary. In a sea-based facility, the water quality in the ocean can change, for example in temperature and oxygen concentration.

– If the fish is trapped in a net pen, they cannot escape and swim to other areas where the quality of water is better. But in a land-based fish farm, the quality of water can be measured via sensors, and thus quickly corrected.

But there can be challenges with the correction. In the ocean, fish such as salmon, migrate between different depths and temperatures. There are therefore many variables concerning light, temperature and depth that the industry needs to understand so that the fish can thrive.

– While there are benefits to being able to regulate the aquatic environment, there is a problem regarding what it should be regulated to. In land-based fish farming, you need to understand all the different variables, which is complicated and difficult, says Albin Gräns, PhD in zoophysiology and researcher in animal welfare at the Swedish University of Agricultural Sciences.

He adds that the regulation of temperature can be an advantage. 

– There are more and more reports of rising temperatures in the rivers, lakes and sea during summer. For a sea-based facility, there is not much you can do because you can’t change the temperature. In a land-based facility however, the risk of wrong temperature will not be a problem if everything is working correctly.

Filter eliminates salmon lice

The system can also filter out bacteria, parasites and diseases, which is a huge advantage as it means that salmon can be raised without salmon lice. As well as leaving large wounds on the salmon’s skin, making it difficult for them to maintain their water and salt balance, the treatments are also very stressful for the fish.

– Far more salmon die as a result of the lice treatment, than from the direct effects of the actual lice, says Albin Gräns. 

However, once an infection has entered the system, it can accumulate faster than in the sea. The fish and water entering the RAS-tanks must therefore be carefully checked for contamination to avoid closure and possible slaughter.

Require density and the right swimming conditions

The land-based fish farms plan to raise between 6 000 to 10 000 tons of salmon each year. But the number of fish can leave a limited space in the sea-based farms when the individuals seek each other out. Kristina Sundell, on the other hand, says that fish need a certain density to thrive.

– A lot of research is being done on which density that is appropriate for different species of fish. Salmon, for example, is a species that needs to be in a group. And if the water quality, such as pH, oxygen and nitrogen concentration, is right you can have more fish per liter of water.

It is not just the water quality and the right density that is important for fish welfare. They also need to swim as they do in the sea. Salmon for example, wants to exercise, so there are tanks especially designed to allow them to swim against a current.

But even though the tanks have a special design, Albin Gräns says that a water tank on land is never as deep as a net pen in the ocean. 

– We don’t know yet how it will affect the fish. We still have a lot to learn about how different species and groups perceive situations and how long it takes for them to recover, for example after crowding and sorting.

More knowledge is needed

Although research has come a long way, more knowledge is needed on how different substances accumulate in the circulating water. For example, there are substances in the feed that the fish do not absorb, as well as substances that the fish excrete that scientists know little about. 

– We therefore need to map out all the substances to ensure that they do not accumulate and prevent the levels from becoming too high, says Sundell.

Albin Gräns agrees that more knowledge is needed.

– We do not yet know how land-based fish farming will affect the fish. There is a real risk that there is not enough knowledge.

All about management and animal care

Land-based farms are considered by many to be the future of sustainable fish farming because it does not affect the marine environment or wild stocks. But Kristina Sundell emphasizes the importance of good management and animal care.

– Technological solutions can provide a high degree of control, which can be positive for fish welfare. But if the living environment is to be ideal, it is all about good management and animal care.