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Recirculating aquaculture systems: The future of fish farming?

March 2, 2010

[Source: Andrew Jenner for The Christian Science Monitor]

Recirculating aquaculture systems cut the pollution and disease that occur in current fish farming operations. Many see it as the future of the industry.

Australian barramundi churn water that is filtered and recycled at Australis Aquaculture in Turners Falls, Mass. The company raises the fish using a recirculating aquaculture system (photo courtesy of Australis Aquaculture).

Inside what looks like a plastic-roofed greenhouse sitting in an old cow pasture are six round, 1,500-gallon tanks (imagine kiddie pools that are eight feet deep), each holding a few hundred rainbow trout. A tangled network of PVC pipes – some as thick as tree trunks, others as slender as pool cues – traces crooked patterns in the cramped space, which is alive with the sound of whirring motors and lots of water, dripping, bubbling, and gushing steadily through the whole convoluted system.

It looks like an ambitious science-fair project. But these are recirculating aquaculture systems at the nonprofit Conservation Fund’s Freshwater Institute, which has researched water use and conservation since 1987. And they represent an exciting new development in food sustainability.

Recirculating aquaculture systems, or RAS, are closed-loop production systems that continuously filter and recycle water, enabling large-scale fish farming that requires a small amount of water and releases little or no pollution.

About 99.75 percent of the water in each unit is continuously cleaned and returned to the fish tanks. Manure filtered from the water during the recycling process is used as fertilizer on nearby farm fields. The nutrient-rich water can also be used to feed vegetables and herbs in large-scale aquaponics systems, which in turn filter the water for reuse.

One of RAS’s biggest benefits is its small “water footprint,” which opens the door to commercial fish production in areas with limited water resources. (The technology is proven for both fresh- and saltwater species).

As efficient as before, but cleaner

The closed-loop RAS design also addresses several major environmental concerns associated with traditional aquaculture, particularly ocean-based “net pen” fish farms where saltwater species are corralled in offshore enclosures.

At these densely stocked net pen farms, concentrated fish waste flows directly into the surrounding ocean. Industry critics often cite a European study that concluded that the pollution from an average salmon farm is equivalent to discharging raw human sewage from a town of several thousand people.

In addition to fish waste, antibiotics and other chemicals administered to the farmed fish can flow directly into the surrounding water. Disease is another environmental concern associated with net pen farming, as the crowded fish are susceptible to outbreaks that can spread to wild populations.

When Steve Summerfelt, who directs aquaculture systems research at Freshwater, began working on RAS development in 1992, his goal was to demonstrate that recirculating systems could produce healthy fish as quickly as traditional production methods.

After that was accomplished within a few years, his research – largely funded by the US Department of Agriculture – has focused on expanding RAS technology to larger scales that remain cost-competitive with other production methods.

That’s no small challenge when competing against offshore fish farmers who don’t pay for their water or face the constant expense of cleaning the water for reuse. But the efficient, cost-competitive RAS technologies developed at Freshwater and elsewhere are catching the interest of commercial fish farmers.

For example, Dr. Summerfelt says, his organization has been talking with about half a dozen fish farms that are considering investing between $5 million and $50 million in RAS production.

“Right now, [RAS] systems are not producing a tremendous amount of fish for the US,” he says. “It’s going to take these $5 million to $50 million investments to start seeing it happen.”

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