From Society for Conservation Biology’s Journal Watch Online:

Long-held suspicions that fish farms act as disease reservoirs for wild populations are well founded, according to findings published this week in Science. University of Alberta mathematical biologist Marty Krkošek and colleagues show that outbreaks of salmon lice Lepeophtheirus salmonis among wild pink salmon Oncorhynchus gorbuscha populations — the direct result of infestations within the open-net aquaculture pens the juveniles must swim past on their migration to the sea — can bring virtual extinction in just four generations. The pressure wild stocks are placed under by the disease risk from fish farms is much greater than that caused by over-exploitative harvesting: the very factor that prompted aquaculture in the first place. It’s surely time for a re-think on fish farming. Source: Krkošek M, Ford JS, Morton A, Lele S, Myers RA & Lewis MA (2007) Declining wild salmon populations in relation to parasites from farm salmon. Science DOI: 10.1126/science.1148744

Also see article in New York Times which quotes:

Ray Hilborn, a fisheries biologist from the University of Washington who was not involved in the study but is familiar with its findings, called the data persuasive and said they raised “serious concerns about proposed aquaculture for other species, such as cod, halibut and sablefish.”

“These high-density fish farms are natural breeding grounds for pathogens,” not necessarily limited to sea lice, he said in an interview. Dr. Hilborn noted, however, that the study involved pink salmon, not species like sockeye or chinook, which are usually larger and presumably less vulnerable to sea lice. Pink salmon are the most abundant salmon species in the northern Pacific.