The water temperature affects the development of the eggs, and they may take over six weeks to hatch. Gradually the developing young search for food, at first only very small stream animals, but eventually their diet consists entirely of invertebrates and small fish. The adults have small but numerous teeth which enable them to grip their very active prey. The pigments in the crustaceans they eat, particularly freshwater shrimps, is responsible for the pink tinge of trout flesh.
River trout can be various shades of brown depending on the water in which they live.
In contrast, sea trout are a rich silver colour, darkening at spawning time when they return to their native rivers. These conditions are essential to allow the extensive growth of aquatic plants, which in turn support the high invertebrate population required as food. While trout may spend their entire lives in a river, some migrate to inshore sea areas. Here the sea trout, as they are called, grow larger and faster on a diet of small fish. But in all cases, trout return to their native river to spawn.