Net benefits: Open Blue’s fish farm pens off the coast of Panama are up to 70 metres below the surface of the water © Mike Budreski/Open Blue

Aquaculture is booming. Fish have been farmed for millennia but it is only in recent times that the industry has achieved vast scale. Farmed fish overtook farmed beef, in terms of annual production by weight, almost a decade ago. And, today, the fish on our plates is more likely to have come from a farm than to have been caught in the wild.

As over-exploitation and climate change threaten wild fish stocks, aquaculture is increasingly framed as a sustainable alternative that can provide a low-carbon, healthy source of protein to the world’s growing population.

Studies suggest that farmed fish has a lower carbon footprint than almost all meats, especially beef.

However, as the industry grows, its harmful effects become more apparent. Global aquaculture production jumped by 527 per cent between 1990 and 2018, compared with a 14 per cent rise in captured fish. In achieving that increase, habitats such as mangroves have been destroyed for shrimp farms and fish waste has polluted the ocean. Sea lice and other diseases have become rife in some densely stocked pens and escaped fish have threatened wild populations.

Many farms also rely on wild-caught fish for feedstock, adding to the dangers of overfishing.

As the sector comes under more scrutiny, some are looking at ways to produce fish more sustainably.

A sprawling, squat building outside Miami, Florida, is being pitched by Norwegian company Atlantic Sapphire as the future of sustainable aquaculture. This land-based salmon farm operates a recirculating aquaculture system (RAS), where fish are raised in controlled conditions. “It has perfect temperature all year round; we can create that perfect environment for the fish,” says Karl Oystein Oyehaug, managing director of Atlantic Sapphire.

527% The global increase in aquaculture production between 1990 and 2018

Underground aquifers supply the farm with water while wastewater is filtered and reused. There are no problems with disease or parasites and no need for antibiotics or pesticides. Being located close to consumers also cuts down transport emissions. “We think that the whole US market, in theory, could be supplied by local farms with a lower carbon footprint,” says Oyehaug.

Controlled environment: Atlantic Sapphire’s land-based salmon farm uses a recirculating aquaculture system, which reduces waste but is energy-intensive © Jakob Gjerluff Ager

But RAS farms have their problems. They are energy-intensive compared with other farms and, if the environment for the fish is not exactly right, the consequences can be catastrophic.

Atlantic Sapphire has experienced several accidents, including one at the Miami facility in March that killed around 500,000 fish. “Most of them have been construction-related challenges . . . we’ve fixed all of them,” says Oyehaug.

Still, experts remain concerned about welfare. “To make [an RAS] cost-effective, you need to pack it with fish,” says Lily Stuart of FAIRR, which advises investors over the effects of intensive farming. This model can cause fish to become stressed and aggressive.

For some, the answer to sustainable aquaculture is at sea. While most aquaculture operations are close to the shore, Open Blue Cobia’s pens are nine miles off Panama in choppy waters. “What we are proposing is potentially less efficient, [and] more expensive, but we believe much more sustainable,” says its chief executive Dario Marchetti.

Huge pens are sunk 30 to 70 metres below the surface of the water. The cobia fish live as they would in the wild and strong currents mean there are no waste problems, according to Marchetti — although critics point out that effluent can still become locally concentrated in the ocean, even if it is quickly diluted.

Twice a day, the pens are brought to the surface to feed the fish with a mix of fish- and plant-based feed. “Our big challenge is to try to reduce the amount of fish component,” says Marchetti.

Feed remains a big sticking point for aquaculture. Despite all the innovation, says Aarti Ramachandran, also of FAIRR: “We don’t see a real strategic move from the industry to solve the feed challenges.” Alternatives to fish-based feedstocks are emerging using ingredients such as soy, insects or algae. But it is yet not clear which will be viable. “They have to pass several tests: affordability, scalability, sourcing, carbon footprint, and also nutritional benefits to the actual fish,” says Stuart.

The race for a fish-free feed also masks a fundamental question about which species are farmed, says Jennifer Jacquet, associate professor of environmental studies at New York University. “We are trying to turn high-level carnivores — Atlantic salmon — into vegetarians, so that we, a mid-level terrestrial omnivore, can continue eating salmon.”

A more sustainable system would be one where we do not have to feed things, says Jacquet. For aquaculture, this means bivalve molluscs such as oysters, mussels and scallops.

“Mussels are one of the most sustainable forms of protein,” says Sarah Holmyard, of Offshore Shellfish based in Devon in England, which is developing what is says will be Europe’s largest offshore rope-grown mussel farm. They require no feed, capture carbon and help diversify marine ecosystems.

Some fish farms are using bivalve molluscs and other species to try to recreate the balance of a natural ecosystem, a concept with deep roots in Asia’s fish farms. A trial in Loch Fyne, Scotland, has cultivated salmon alongside seaweed and shellfish, which feed on the farm’s waste.

For aquaculture to tackle its challenges, says Jacquet, it must examine all of its impacts, including carbon emissions, feed, pollution and welfare and “really reflect on how it should grow for a better, more sustainable future”.

‘Mussel farming is the future’: Q&A with Offshore Shellfish’s Sarah Holmyard

What does Offshore Shellfish do?
We run a rope-grown mussel farm off the south Devon coast. Once fully developed, we will be Europe’s largest offshore rope-grown mussel farm, producing over 10,000 tonnes of mussels per year. Our ethos is: eat mussels, save the planet.

How do the mussels grow?
We put collecting ropes in the water for spat (very young mussels), we then harvest the spat and put it on to new lines to ensure it’s spread out to the right density and has space to grow.

How are they sustainable?
Mussels are a completely self-sustaining food source; we have no input into how they are created apart from providing a home for them. We use no chemicals and no feed; the mussels feed on the plankton in the water. As they grow they sequester carbon from the atmosphere and lock it up in their shells. They also help sustain a healthy marine ecosystem.

Mussel farming is often overlooked but it is the future. It ticks so many boxes in terms of feeding the world, saving the planet, reducing carbon and it’s also a lovely place to be — out at sea.

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