The rainbow trout, worth £15,000, escaped from the Scot Trout farm at Ardchattan on Loch Etive in the early hours of Saturday morning.
Wild fish groups said it is the latest in a long sequence of releases of farmed fish affecting the important River Awe system.
Roger Brook, chairman of the Argyll District Salmon Fishery Board, said: "We are bitterly disappointed but hardly surprised to have yet another major escape from a rainbow trout farm located adjacent to the mouth of the River Awe, Argyll's most important salmon river."
Anger over Escape of Trout from Fish Farm
UK - Anglers yesterday condemned the escape of about 4,000 fish from a trout farm in Argyll.