Brown Trout
salmo trutta fario
Having been introduced by anglers, Brown trout can now be found all over the world in fresh water lakes, streams and rivers. They are very sensitive to the quality of the water; temperature, oxygenation and pollution. The cool, rapid flowing streams and rivers and the high water quality found in the Highlands of Scotland provide an ideal environment for trout and for anglers
Life cycle
Egg stage
In the UK, spawning takes place from October to December, a long warm summer will cause later spawning. Trout Fry hatch 3 to 5 months after spawning depending on the temperature of the water, hatching quicker in warmer water. If the water is too warm then the eggs may not survive due to lack of oxygen. For this reason the eggs are usually laid high upstream in oxygen rich water. Depending on her size, the female may lay up to 4,000 eggs 99% of which will probably not survive beyond the fry stage.
Alevin stage
Newly hatched trout carry their yoke sac with them and are dependent on this for sustenance. The sac is absorbed as the alevins develop their digestive systems. In good conditions this stage will last for about 20 days during which time the alevins will avoid light by hiding in the gravel. At the end of this stage , when the yoke sac has been absorbed the alevins become fry and are about an inch long.
Fry stage
The fry can feed on live prey, if only plankton, but are now very vulnerable to predators including larger cannibalistic trout. Their markings and colouring will start to appear after 3 to 4 weeks. Though they may change their colouring throughout their life to adapt to their environment. As they grow the fry will move, usually downstream, to find food. Where they end up is a main factor in their development and eventual size.
In good conditions, in the wild, trout can reach 8 inches (20cm) in length in about 3 years, more than this can be considered exceptional. Where conditions do not permit trout may never exceed 5 or 6 inches but still live a relatively long time. They feed at first on insect larvae, freshwater shrimps, and insects on or below the surface of the water. As they get larger they become more predatory feeding on smaller fish, and where food is plentiful a predatory trout can put on 3 or 4 lb (~2kg) a year. Older, larger fish feed purely on smaller fish and are fiercely territorial. A few brown trout will live for decades.
Behaviour of brown trout
Brown trout are shy fish, they like to stay close to cover, large stones, overhanging banks, deep pools and weirs. They are territorial and will often occupy the same place for years, leaving only to find a place to spawn and returning again afterwards.
Trout have good vision and can see brightly dressed townies well up the river bank. They have only one small blind spot directly behind them, so to successfully fish for trout it is a good idea wear suitable clothing - camouflage and some kind of hat to break up the human shaped outline. It is also good to keep quiet and not announce your presence with a beer fuelled sing song and if your children are addicted to stone throwing then leave them at home. Trout will often "sit" facing upstream where they can see food coming towards them on the current. In slow moving water or lakes larger trout will spend more time in deeper water.
Early in the fishing season when the insect life is not yet "buzzing" trout will mostly feed close to the bottom. As the weather starts to warm, larvae start to rise and so do the trout. In much warmer weather when the water has also warmed, daytime activity slows down and morning and evening become the active times for trout. Fry are now on the menu they get chased to the surface in shoals, larger trout tend to remain deep, but there can be a lot of surface activity. Towards the end of the season when the insect life is also nearing the end of its season flies will be taken from the surface as they lay their eggs or lie spent.