The diagram illustrates the life cycle of salmon.
At the initial stage, salmon spawn in upper rivers by depositing their eggs in slow-moving waters. Eggs are placed among reeds and small stones for defense. Approximately 5 or 6 months will elapse before these eggs incubate and hatch into fry, which will be around 3 to 8 cm in length. Once emerged, fry swim downstream, start their life, and occupy the lower river or estuarine environments of faster water, living for about 4 years and growing up. Almost at the end of this life stage, the fry develops into smolts, 12 to 15 cm long.
Following this transformation, the smolt leave freshwater, migrate to the open sea, and begin the adult phase. The salmon will remain in the marine environment for around 5 years, further growing until they reach a full adult size of 70 to 76 cm. When they complete their oceanic development, the salmon will return to the upper river to spawn. They will spawn the eggs in the same area they were hatched in, completing the cycle. The adult salmon usually die after spawning – therefore the return journey is their last dramatic act.
Thus, the whole process involves three important life stages which include fry, smolt, and adult salmon. These stages are established along a gradient of habitats, beginning in slow-moving freshwater, passing through fast currents, and ending in the open sea. The life cycle of salmon is amazing and unique due to their relocation from freshwater to saltwater and vice versa.