Salmon begin their remarkable life-cycle from eggs which have been laid, fertilized, and covered with gravel (sometimes sand) in the upper reaches of a river or stream. Water must flow through the gravel to supply oxygen.
After incubation, tiny alevins (pronounced AL-i-vinz) emerge from the eggs. Alevins have a yolk sac below their bellies which contains sufficient nutrition for their early development. They do not emerge from under the gravel during this alevin stage, but stay there for protection against predators until their yolk sac is fully absorbed.
You can read the rest of "Pacific Salmon — The Ocean's High Achievers", here. Addendum: This just in, a new study indicates geomagnetic imprinting in salmon!
When they emerge they are 3-4 centimetres (about 1 1/2 inches) long, and are called fry. They make their way to larger freshwater pools for protection from sunlight and predators. The time which fry stay in fresh water varies with the species, and can be from two to 20 months.