If one creature can show us that genetics doesn’t entirely explain the differences in form that life takes it is brown trout (Salmo trutto). Little freshwater dwelling brown trout, sea faring trout and giant ferox trout are all the same species. Golden brown backs, yellow bellies and red and black spots make brown trout far more colourful than their name suggests. They inhabit well oxygenated, cool and fast flowing freshwater. They catch their diet of small fish and insects by ambush. When it is time to spawn they mingle with fellow brown trout, and also with visiting sea trout.
INDISTINGUISHABLE
Sea trout spend the first year or two of their life indistinguishable from brown trout. But then they change. Outwardly they turn silver, inwardly they become able to live in saltwater. Gathering together, these salt adapted trout migrate en masse to the sea. Finding richer sources of food there allows them to grow bigger than brown trout. Sea trout return to their natal river to spawn. While closely related salmon tend to perish after spawning, most sea trout retain enough vitality after spawning to travel back to the sea.