Advances may make fish farming a healthy prospect, even for inner cities

Science News, May 13, 2000 by Janet Raloff

An economic renaissance is apparent in much of Baltimore, including the cobblestoned, 225-year-old Fells Point neighborhood that hugs a northern edge of the city's Inner Harbor. Some 18th-century storefronts display antiques, others feature homemade ethic cuisine. Construction on towering new hotels booms overhead.

Inside a nondescript, greenish-beige waterfront warehouse, marine biologists are laboring over their own contribution to this area's economic revitalization. The ambitious goal of these researchers at the university or Maryland's Center of Marine Biotechnology (COMB) is to redesign aquaculture, bringing teeming tanks of seafood to urban centers. Though they're starting with Baltimore, the next site could be Detroit, Iowa City, or even Phoenix.

At the Virginia Institute of Technology in Blacksburg, researchers are spearheading similar efforts to move aquaculture to nontraditional venues--in this case, depressed farm towns.

"For folks used to the commitment that a farm takes, such as milking dairy herds twice a day, fish may represent a welcome break," observes George J. Flick. A full-scale prototype that his Virginia Tech team is constructing in rural Saltville, Va., should "take at most only a couple hours a day to run," he says.

Key to the efforts of both groups is an emerging technology known as recirculating-tank aquaculture.

Conventional aquaculture raises fish in the open. Fish farmers usually corral marine species--sometimes in bays, other times within pens floating in the open ocean. Growers of freshwater species usually rear animals to market size in outdoor artificial ponds. These systems all rely on large volumes of clean water flowing to the fish and carrying waste away.

Over the past decade, such operations have been coming under intense criticism for fouling the environment.

Moving to tanks that recycle their water would not only limit the input of clean water but also reduce--and perhaps eliminate--discharges of waste streams. To achieve this, fish farmers have been adapting some of the technology that keeps finned specimens alive in home aquariums and zoo tanks. However, because the purpose of fish farming is not display, the aquarists' glass-walled tanks have given way to huge, opaque fiberglass pools--many holding at least 25,000 gallons of water.

Moreover, as the aquatic analog of cattle feedlots, aquaculture's recirculating tanks must nurture a far denser population of fish than standard aquariums do. They must also foster quick growth--while not compromising fish health. Overall, it's a tall order.

Yet if that order can be filled affordably, this technology could open aquaculture to new species and applications, notes Yonathan Zohar, COMB's director.

For instance, scientists have begun rearing fish for restocking the wild. Among them are species threatened with extinction. For some, their early life stages require more protection or more tightly controlled conditions than open pens or pools offer.

Zohar's team is breeding a tasty marine fish, known as bream, that doesn't naturally inhabit U.S. waters. The COMB researchers weren't permitted to import the fish until they assured federal regulators that none of the finned stock could escape, even into sewers.

Though a few commercial fish farms have already begun investing in recirculating-tank technology, such operations remain niche players in the United States' $900 million aquaculture industry, observes Jim McVey, director of aquaculture programs for the Commerce Department's National Sea Grant College Program in Silver Spring, Md. However, he argues, advances in this emerging technology leave it poised to assume a major role in satisfying the nation's appetite for freshwater fish and seafood.

Each year, the United States imports fish and shellfish valued at some $14 billion, McVey notes. Led by $2 billion worth of shrimp, this industry has evolved into one of the largest import sectors. "In terms of natural products," he explains, "it's second only to oil."

While precise numbers aren't available, McVey estimates that 60 to 80 percent of those aquatic imports have been farmed. He'd like to see the United States reclaim much of the market.

Because the young of marine species tend to be "smaller and more delicate than their freshwater cousins," he observes, they have been difficult to raise in captivity. Moreover, to be attractive to growers, stocks must spawn on demand, so that commercial-size fish can come to market year-round. Yet even in conditions emulating their spawning environment, the captive females of many marine species don't ovulate.

The coddling that recirculating systems permit makes this technology the best hope for growing marine fish, McVey says. With it, growers can precisely control temperature, wave action, oxygen supplies, nutrients, and daylight. There is a catch, however. Such operations today cost more than ordinary fishing or open aquaculture.

That's why growers who've begun investing in this technology tend to raise only high-value fish. Zohar acknowledges that economics provides one reason that his team works with gilthead bream. U.S. imports of bream now command up to $14 a pound.