In Britain the rainbow trout is thought of purely as still water fish. It is not popular in rivers as its aggressive feeding behavior will replace the native brown trout.

A Rainbow trout that is stocked into a large water like a reservoir or gravel pit will slowly change shape and color over the months as it reverts to natural feeding. Much of the spotting will disappear with the fish developing a more silver color. The fins will also develop as the fish has more room to move and further to swim.

They contrast with the giant rainbows stocked into many small waters. These bloated monsters reared on a super rich diet of pellets, can never sustain their weights in such small waters and need to be caught quickly if they are not to loose condition. Usually they are caught on the very day they are stocked.

Brown Trout. Brown Trout are the fish that started fly fishing and are fished for across the world today. Sadly Brown trout are fast becoming an endangered species in England and Wales due to water pollution, abstraction of rivers, urban development and acid rain. This is a threat to brown trout as they require a good flow of oxygenated water to breed. The picture is much brighter in the west of Ireland and Scotland where the large lochs support good heads of fish.

Brown trout are much slower growing than rainbows, but they can reach double figures in weight in the wild in ten years if they switch from an insect to a small fish diet.