Trout lay their eggs in gravel nests called redds between November and January when the water is cold. The eggs hatch after about 90 days, and the young trout called alevins live in the gravel and feed off their yolk sacs. Once the yolk is absorbed, they emerge as fry and must find food and shelter quickly. After one year, they are called parr and live similarly to fry but will move downstream with the current. Adult trout establish territories with food and shelter, and in winter migrate to spawn, repeating the cycle.

1. Orkney Trout Cycle

2. Egg Spawning
Trout lay their eggs in nests in river gravels,
known a redds. The female builds the nest,
usually between November and January
when the water is cold and carrying lots of
oxygen, because that is what the eggs need
to hatch.

3. Egg Hatching
As the eggs that have just been laid develop you start to see the ova develop
with them. This is called the eyed ova stage. The eggs hatch more quickly if the
water they are in is warm. In Orkney we usually try to keep the water at 5
degrees meaning that the eggs take roughly around 90 days to hatch. The
newly hatched trout are called alevins, and they live in the gravel having yolk
that is attached to their bodies for about 25 days after hatching to feed on.
Once again they grow quicker in warmer water.

4. Fry
Once the yolk of the alevins has been eaten, the alevins become fry,
emerge from the gravel and feed on tiny insects in the water. A lot of
brown trout die in this stage. They are only a few centimetres long and
consume a lot of energy. They have to find plenty of food quickly as
possible. They usually keep away from other fry and are territorial and
need stones and plants to hide in. they also need shallow water (1-
40cm) and isn’t fast flowing.

5. Parr
A one year old trout is called a Parr. They are
small with marks on their scales and they lose
these when they age. They live in the same habitat
as fry with stones. They will gradually drop
downstream with water flow rather than fighting the
stream going up.

6. Adult Trout
Adult trout have a territory that gives them a good supply of food and a
place to hide from predators, preferring deeper pools. In winter they
migrate, perhaps miles up river to spawn. Brown trout can live from 5 to
20 years.
The whole Brown trout cycle repeats itself.

7. Adult Trout
Adult trout have a territory that gives them a good supply of food and a
place to hide from predators, preferring deeper pools. In winter they
migrate, perhaps miles up river to spawn. Brown trout can live from 5 to
20 years.
The whole Brown trout cycle repeats itself.