Life cycle of the Brown Trout &

Sea-Trout

October- December

Depending on weather conditions. Adult Brown Trout start migrating upstream. It’s called the run. They need to reach the shallow fast flowing upper reaches of the burn to lay their eggs (ova) in a shallow depression in the burn bed, the redd . The pink eggs (3 to 5mm) are then fertilised by the male releasing milt.This stage of the trout life cycle is called spawning.

Alevins

January – February

The number of eggs depends onthe size of the trout. Usually about 800 to 1200 ova per kilo. After 2 to 3 months, the eggs hatch into alevins. These are see-through and have a yolk-sac which they will feed on for 4 to 6 weeks. They are very sluggish and try and save energy to make the yolk sac last!

March

4 to 6 weeks after they’ve hatched,the alevins have absorbed their yolk sacs and have developped markings on their sides: they are called fingerlings or fry and will now have to feed on zooplankton, daphnia, insects and other worms.During the first year of their life, they will barely move more than 200 yards away from where they were born.

For 3 to 5 years in the burn.

After about a year, the fingerlings will have grown to 5-8 cm and will behave like an adult trout, feeding on insects, larvae, molluscs and worms. The size of their preys gets bigger and as the trout grow they tend to move into deeper and slower parts of the burn or river. If it’s a burn flowing into a loch, the fish will move into the loch after a couple of years.

Some brown trout have developed a migratory gene which allows them to leave fresh water and spend most of their life at sea. They’re called sea-trout. The migration usually happens in late spring and autumn. The fish then turn silver and become smolts. They then adapt to life in the sea and grow much quicker and bigger than their freshwater cousins. However, they still need to spawn in fresh water, exactly like brown trout .