Few fish are more variable in colour than the brown trout (or brownie). Some are silver with several small black spots, others are almost black with a few large red spots. The colour depends on habitat, but most are golden brown with large dark brown spots on the sides, back and dorsal fins and a few large red spots here and there.
Like the other members of the salmon family, the brown trout has a small, rayless adipose fin between the rayed dorsal and tail fins. Its mouth is full of numerous small teeth, and its upper jaw-bone extends well past the rear of the eye.
Unlike the rainbow trout, the brownie can only thrive in cool, highly-oxygenated water. It is usually found in the upper reaches of rivers and chalk streams, and in some large lakes and lochs where the water is unpolluted. The species, native to Britain, is abundant all over the British Isles but this is largely the result of artificial stocking for the benefit of anglers.
The brown trout leads a solitary life-style. For most of the year it adopts a single, deep lie that gives shelter from predators, easy access to food and comfort out of the main force of the current. Generally, the brownie is a non-migratory fish and, once it has found a good lie, may never move far except in a drought, a spate or to spawn.
Many brown trout are farm-reared and released into a fishery when they have reached a takeable size; such fish are usually much larger than the average wild trout.
Living alongside a conveyor-belt of food carried by the main flow of the river, the brown trout doesn’t usually have to venture far to feed. It has good vision and is one of the few members of the salmon family to feed at night.
Stillwater trout have to be more active in their search for food – they cruise the margins and bed of the lake during the day, and move to the surface at night to feed on insects. The brownie is a predatory fish, and even eats its own young if plentiful.
Matching the insects the fish are taking is an important part of the skill of fly fishing. Early in the season (April-May) the brownie tends to feed in deep water on nymphs, shrimps and caddis larvae. As the water temperature rises and insects become more active, the fish moves to the surface to feed on upwinged flies, sedges and midges. Anglers should try to ensure that the artificial nymphs and dry flies they use look and move as much like the natural insect as possible since brown trout are wary of any unnatural-looking flies.
The brown trout needs shallow, fairly fast- flowing water for spawning. Those living in lakes and lochs move into the feeder streams in the early autumn to spawn. Spawning occurs between November and January – the female digs two or three hollows (redds) into the gravel bed with her tail, in which she lays her eggs. At the same time the male fertilizes the eggs, and the female then covers the nest with gravel. Eggs not buried properly are quickly eaten by other predators.
Within a few weeks the eggs hatch, and the larvae (known as alevins) feed first on their egg sacs and then on small water creatures until they are about five months old. Since growth is dependent on food supply, size is variable, but after a few years most wild brown trout reach a length of 20-38cm (8-15in).