By Dan Gibson
In a series of indoor tanks 40 miles south west of Miami, Florida, five million fish are swimming in circles a very long way from home.
The fish in question are Atlantic salmon, which are far more typically found in the cold waters of Norway's fjords or Scotland's lochs.
As the species is not native to Florida, and would be unable to cope with the state's tropical heat, the water tanks are kept well chilled, and housed in a vast, air-conditioned and heavily insulated warehouse-like building.
The facility, called the Bluehouse, opened its first phase last year, and intends to be the world's largest land-based fish farm.
Targeting an initial production of 9,500 metric tonnes of fish per year, its owner - Atlantic Sapphire - plans to increase that to 222,000 tonnes by 2031, enough to provide 41% of current US annual salmon consumption, or a billion meals.
The company is at the forefront of a growing movement in Europe, Asia and the US towards land-based, indoor aquaculture. But what could it mean for traditional sea-based salmon farms, and most importantly - what about the welfare of the fish?
"When we started [exploring the concept] 10 years ago, people thought we were completely crazy," says Johan Andreassen, chief executive of Atlantic Sapphire, which is a Norwegian-owned business.
"No-one was recognising that raising salmon on land would ever become financially viable, or even doable. Then the incumbent industry started to become more questioning. But they were waiting to see how the technology evolves.
"And now with Atlantic Sapphire, we have proven that it's possible. So now it's a question of how competitive can this be, and how large can it become."
The technology that enables Bluehouse to operate is not new, but using it on a commercial scale only became viable in the last few years.
Called "recirculating aquaculture systems", or RAS for short, they control everything from the temperature, salinity and pH of the water, to its oxygen levels, artificial currents, lighting cycles, and removal of carbon dioxide and waste. The latter are filtered out, and treated water is reused.
As it is a closed-loop system, the salmon are not exposed to seaborne diseases and parasites, so unlike sea-based farms, Atlantic Sapphire says its fish do not need to be treated with antibiotics or pesticides.
Atlantic Sapphire plans to expand Bluehouse, pictured, across its 160-acre site
"In general, compared to the [sea-based] industry, we have the lowest disease incidents and the lowest mortality rates," says Neder Snir, chief technology officer of Israeli firm AquaMaof. His company has now designed technology for 10 such RAS fish farms around the world.
"And it is important to note that this occurs without the use of any antibodies or vaccinations," adds Mr Snir. "Because of the fact we're isolated and controlled."
Atlantic Sapphire has already invested $400m (£287m) in its US facility, and plans to spend $2bn in total. By 2031 it intends to have four million sq ft (372,000 sq m) of tanks across the 160-acre (65-hectare) site.
But why did a Norwegian firm choose to build a vast salmon farm in Florida? Firstly so that it can supply the US market without having to fly in the harvested fish from Europe. And secondly because of the unique nature of the southern state's geology.
Atlantic Sapphire wants its Florida farm to provide 41% of total current US salmon consumption by 2031
In very simple terms, Florida sits on top of two separate aquifers - a fresh water one nearest the surface, and then a salt water one lower down.
As salmon needs fresh water when it is young, and then salt water when it is older, Bluehouse has a ready supply of both. And somewhat controversially, it can then inject what waste water it does produce down to an empty layer in the rock even further below.
The company says this layer is entirely isolated and therefore cannot contaminate the wider water supply. It adds that only "minimal quantities of treated waste water [are released] per strict local regulations".
When it comes to wishing to shorten supply chains, Mr Andreassen says that the coronavirus pandemic has focused people's minds about the issue.
"The value proposition has become much better since Covid," he says. "People want short, lean value chains with increased traceability, where fewer people are touching your food before you eat it.
"And the cost of air freight, with the passenger air travel industry on its knees, has been pressurised through the roof."
The fish farm tanks require constant monitoring to maintain the correct water quality
However, the Bluehouse project has not been all plain sailing. In July last year an issue with its water quality meant that, in the words of Mr Andreassen, "we faced a situation where we risked large [salmon] mortalities". To avoid this outcome, the company decided to "emergency harvest" 200,000 fish before they had reached their full 20-month-old maturity.
Another design problem in March this year caused further fish deaths, the firm had to report. And earlier this month it was reported that three workers at the facility had to go to hospital for treatment following the release of an unknown gas.
Unsurprisingly, animal rights group People for the Ethical Treatment of Animals (Peta) is damning of Bluehouse and the 40 or so other firms developing such land-based fish farms around the world. These include a planned barramundi farm in Arizona.
"Fish farms [whether at sea, or on land] are pits of filth," says Dawn Carr, Peta's director of vegan corporate projects. "Fish are not fish fingers with fins, waiting to be cut apart, but feeling, thinking individuals capable of joy and pain, and they belong to themselves, not to humans.
"Raising fish this way is wretchedly cruel and certainly unnecessary."
Mr Andreassen says that the welfare indicators of the salmon, such as fin shape and swim speed, are constantly monitored at Bluehouse.
And despite such concerns, Atlantic Sapphire's Floridian salmon has already proven very popular with US consumers. Last year its Bluehouse-branded salmon fillets sold for $12 per kg, more than double the price of Norwegian imports.
So should Scotland and Norway's traditional sea-based salmon farmers be worried?
Ragnar Tveteras, a business professor at Norway's University of Stavanger, and an expert on the industry, says questions remain about the viability of the land farms.
"I think there is a structural challenge there with respect to energy use, and then implicitly contribution to CO2 emissions," he says. "And I'm still waiting for some better clues of what the cost performance will be.
"I'm not worried about the demand [for their salmon], but I worry what prices will emerge, and what that will mean for the [financial] returns of these land-based farms. I'm afraid for some it won't be profitable."
Alan Tinch, Scotland-based technical director at aquaculture services firm Benchmark Genetics, works closely with Scottish fish farmers. He predicts that they will stick to sea cages, although he says some do now rear young salmon, called smolts, in on-land tanks, before transferring them to the sea facilities.
"My view is Scottish salmon's advantage is in the quality reputation that it has, and part of that quality reputation is that it's produced in high-quality seawater in conventional cage production," he says.