Eosalmo driftwoodensis found in 50 million year old Eocene sediments in Canada is the oldest known fossil fish with salmon characteristics. The fish was found in all ranges of sizes and is believed to have lived (and died) in a freshwater lake. Because of the range of sizes found it is thought that the sea going nature of salmon may have evolved later and Eosalmo was more akin to a trout in habit. Eosalmo has been found in a number of locations in Canada but the first was described by Mark Wilson, a professor at the University of Alberta, from Driftwood Creek near Smithers in British Columbia.

Note: Eo = new, hence name Eosalmo or "Newsalmon"

Eosalmo is, however, a mere youngster as far as fossil fish go:

530 Million years old from China

450 Million years old from Africa

Here's a video about 1 million year old fossil Sockeye salmon:

[ame="http://www.youtube.com/watch?v=92x0tK_umOs"]YouTube- Million-Year-Old Salmon: Cruisin' the Fossil Freeway[/ame]