An official investigation into the collapse of B.C.'s Fraser River sockeye stocks is getting underway in Vancouver.

The Cohen Commission of Inquiry launches the first three days of what is expected to be a lengthy and technical probe into the disappearance of almost 10-million fish from last year's Fraser River sockeye returns.

Only about one-million fish returned to spawn, prompting the federal government to order an investigation led by B.C. Supreme Court Judge Bruce Cohen.

A discussion paper released in advance of this week's hearings indicates the inquiry will examine everything from fish biology to the organization of the Department of Fisheries and Oceans.

One of the most controversial aspects of the inquiry is expected to focus on the role of open-pen fish farms dotting the B.C. coast along wild salmon migration routes.

Critics believe lice and other contaminants from the fish farms are deadly to wild salmon but the discussion paper says Fraser River sockeye experience a "suite of impacts" which must all be evaluated in order to understand the collapse.