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Parasite infestation is another chronic problem of high-density seafood farms. One of the most damaging organisms is the sea louse, which breeds by the millions in the vicinity of captive salmon. In 1989 Peter Mantle, who owns a wild salmon and sea-trout sport fishery in Delphi on the west coast of Ireland, discovered that young trout returning to his river from the ocean were covered with lice that were boring through the trouts' skin and feasting on their flesh. The sea lice were breeding near newly installed salmon farms in the inlet fed by his river. By the time the salmon farmers started dosing their pens with anti-sea-lice chemicals, the sea-trout fisheries of the west of Ireland were effectively dead. "Sea-trout fishing was sustainable and eco-friendly," says Mantle, "but the salmon farms killed it off within a decade."
In the long run, wild-fish stocks may face an even greater threat from captive fish escaping and competing with or consuming native fish, or cross-breeding with them and diluting the genes that have helped them survive. Fish escapes are common: nets are ripped open by predators or storms, fish in ponds get swept into channels by rainfall, others are released accidentally during transport. Bighead and silver carp that were introduced to China's plateau lakes in the 1950s have cleared those waters of whole species of indigenous fish. And Asian carp, which were introduced in Mississippi Delta catfish ponds to control parasites, escaped in the early 1990s and have migrated up the Mississippi and Illinois rivers to within 25 miles of Lake Michigan, threatening native fish with their voracious feeding habits.
Experts say aquaculture done right could easily feed the world without polluting it. A favored method of environmentalists is the hard-walled pen system that isolates the fish from the surrounding water in 40-ft.-deep tanks and catches their waste in the bottom. Even more secure are containment ponds built onshore into which seawater is pumped. Agrimarine Industries in Cedar, B.C., is testing a site with eight tanks 100 yds. from the sea and 40 ft. above it. But production costs are expected to be about $2.20 a fish--double what it costs to raise a salmon in a net pen.
Although salmon farming for decades has been a highly profitable industry and shows strong promise for the long term, profits are being squeezed today--making it more difficult for operators to adopt more expensive, eco-friendly methods. About 75% of salmon-farming firms are relatively small and privately held and don't make their finances public. The large, publicly held companies in the business--including Dutch food producer Nutreco Holdings NV and Norwegian seafood giants Fjord Seafood ASA, Stolt Sea Farm and Pan Fish ASA--are feeling the pinch. Pan Fish recently reported a quarterly operating loss of $18.5 million.