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Salmon split their life between fresh water and
the sea. They are born in fresh water, where adult salmon lay and fertilize
their eggs in a nest called a "redd".
The eggs begin developing right after fertilization,
and will hatch after about 180 days at normal water temperatures. The
fertilized pink or orange eggs pass through the eyed egg phase, which
is when their eyes are clearly visible in the egg, to the point of hatching. 
The just-hatched fish are called alevins, and still
have a yolk sac attached to their bodies, which they feed on until its
gone. They have not yet completed their development, and can’t
swim, so they feed on the yolk until they are ready to go. They grow
eight fins, which they need to maneuver in the water.
When they can swim, the fish are called fry, or age
0+ parr. For most of the rest of the time they spend in fresh water,
the juvenile salmon are called parr. After the parr have grown to 10
–20 cm in body length, they become smolts and make a springtime
migration from the river to the sea.
It is at the smolt stage that the salmon develop
salt pumps that can dump the masses of salt they get every time they
eat something at sea. Once at sea, the salmon find much more to eat,
and they grow very fast.
Some salmon will return to their river for spawning
after one year at sea. These are called grilse.
Fish that stay at sea for two or more years are
called salmon. Spawning time — when the female salmon lay their
eggs and the male salmon fertilize the eggs — is in the autumn.
Salmon that have finished spawning become very skinny, and are called
kelts. Some die, but others return to the sea in either the autumn or
the next spring, and will come back to spawn again. Unlike people, salmon
will continue to grow all their lives. The biggest salmon are the oldest.
The salmon’s life cycle adapts the fish to survive
in the best way possible in the specific conditions of their home river,
or even the tributaries of the home river. For example, some tributaries
are steep with fast currents and waterfalls to jump. Here, the salmon
that return are large and powerful, so they can get up the river. These
fish will spend more than one year at sea. In nearby tributaries with
slower currents, the fish may come back after only one year at sea.
In some places, salmon don’t go to sea. These
are called landlocked salmon, or ouananiche. In the past, the ancestors
of this fish went to the ocean. However, as rivers dried up or river
courses changed, they found themselves trapped with no way to sea. Now
they manage to complete their life cycle entirely in freshwater, but
they are much smaller than their sea run relatives.
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