The diagrams illustrate the life cycle of a salmon, outlining the key developmental stages from egg to adulthood.

Overall, the life cycle of a salmon comprises three main environments: the upper river, the lower river, and the open sea. The process begins with spawning in freshwater and concludes when mature salmon return to the same location to reproduce, thereby completing the cycle.

Initially, adult salmon lay their eggs in the upper course of the river, where the water flow is slow. After hatching, the young salmon, known as alevins, remain sheltered among the gravel while absorbing nutrients from their yolk sacs. As they grow, they develop into fry and gradually migrate downstream to the lower river.

In the lower section of the river, characterized by faster-flowing water, the fry continue to grow over a period of approximately 4 to 6 months. During this stage, they develop the strength and adaptations needed for the next phase. Once they become smolts, they begin their journey toward the ocean.

Upon reaching the open sea, the salmon spend roughly one year maturing into adults. During this time, they undergo significant physical development and prepare for their return migration. Eventually, the mature salmon swim back upstream to the upper river, often to the exact location where they were born, to spawn and restart the life cycle.