Feeling louse-y

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Commercial fish farms are a booming business. But the practice of raising fish in underwater pens is spreading a pesky parasite that's decimating wild salmon populations.

A study by Canadian biologists recently found that fish farms cause outbreaks of tiny flesh-eating crustaceans, called sea lice, that latch on to fish in the wild. The lice-infested farms located in Canada's British Columbia province are situated along the migration route that newly hatched pink salmon take to reach the Pacific Ocean. As the wild salmon swim past the farms, they pick up the deadly hitchhikers.

"Young salmon don't have scales, which act like armor for adults," says Alexandra Morton, director of the Salmon Coast Field Station in British Columbia. That makes them vulnerable to sea lice, which killed up to 80 percent of the baby salmon in the study, The scientists fear that unless farming practices change, local wild salmon will soon be driven to extinction.

AMOUNTS OF CANADIAN-FARMED AND WILD-CAUGHT SALMON

Fish farms now produce more than two thirds of the salmon the world eats. But that wasn't always so. In which year did the amount of farmed fish in Canada surpass the amount of wild salmon caught?

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