Around the world, people are eating more seafood than ever before. Demand is increasing due to growing populations, and because health-conscious consumers are choosing seafood more often. To help supply the global demand for seafood, people are raising fish, shrimp and oysters like farmers raise cattle and chickens. Today, almost 20% of our seafood comes from farms. The ecological impact of fish farming depends on which species are raised, how they are raised and where the farm is located.

Fish farms depend on wild fish
While farmed fish and shellfish can supplement our seafood supply, they can't replace the variety and abundance of seafood from the wild. Most seafood farms depend on healthy wild populations to supply eggs or young that the farmers raise for market. Many fish farms also depend on wild fish, like anchovies, as food for the farmed fish.

Farmed shellfish are a Best Choice Most oysters on the U.S. market, and many of the clams and mussels, are farm-raised. These shellfish filter tiny plankton out of the water for their food, so they need no supplemental feeding. Shellfish can even improve water quality as they clear the water of excess plankton. And because shellfish for human consumption must come from clean water, shellfish farming often spurs efforts to keep coastal waters clean.

Clams are raised in special beds on sandy shores, where their harvest does little to disturb the ecosystem. Oysters and mussels are often raised in bags or cages suspended off the seafloor, doing little damage as they're harvested.

Net-pen farming can be a messy business
Many farmed fish, including most farmed salmon, are raised in net pens, like cattle in a feed lot. Thousands of fish concentrated in one area produce tons of feces, polluting the water. Diseases can spread from fish in the crowded pens to wild fish. Antibiotics and other drugs used to control those diseases leak out into the environment, creating drug-resistant disease organisms. And if farmed fish escape their pens, they can take over habitat from wild fish in the area. While the U.S. has laws to protect the environment around coastal fish farms, many nations that supply farmed fish to U.S. markets do not.

Shrimp farming can harm the coast
In Thailand, Ecuador and many other tropical nations, coastal forests of mangroves once sheltered wild fish and shrimp, which local people caught to feed their families. Mangroves also filter water and protect the coast against storm waves. Many mangrove forests have been cut down and replaced with shrimp farms that supply shrimp to Europe, Japan and America. After a few years, waste products build up in the farm ponds and the farmers have to move on. The local people are left with no shrimp farms—and no mangrove forest.

Far from the sea may be best
The best way to raise fish may be inland, far from coastal waters where wild fish feed and breed. Tilapia, a plant-eating fish, is easy to raise, and produces protein for people without using wild fish as feed. Catfish and trout are raised inland in the United States. All of these fish can be delicious alternatives to ocean-farmed shrimp and salmon. Even shrimp and salmon farming can be moved inland, where wastes are easier to handle. U.S. shrimp farmers are experimenting with enclosed, recirculating systems that filter wastewater and can be located far from the coast.

Information courtesy of Monterey Bay Aquarium. Visit their site. www.montereybayaquarium.org