Diagrams illustrating the life cycle of salmon from egg to adult, as well as changes in salmon populations in North America from 1970 to 1999.
In general, the life cycle of salmon consists of several distinct stages, beginning with spawning in freshwater and ending with the adults returning to spawn and dying.
Salmon eggs are laid in freshwater and hatch into Alevin larvae after about 3 months. At this stage, the fry live under rocks and absorb nutrients from their attached yolk sac. As they grow larger, they develop into fry and begin to swim independently. The salmon then transition to the Parr stage, which lasts for several months and develops the characteristic stripes on their bodies.
At 1 to 3 years of age, the salmon become Smolts, begin to gather in schools and migrate to the ocean. In the sea, they develop into adults, living from 1 to 6 years. When fully mature, salmon return to freshwater to spawn, becoming spawning salmon. In the fall, adult salmon change color and return from the ocean to the place where they were hatched. To prepare for the long journey, salmon return to the estuary, where they grew up, readjusting to freshwater. Then, the salmon begin the journey upstream to spawn. After spawning, they die within about 2 weeks, closing the life cycle and starting a new one.