The Life Cycle of Salmon The diagram briefly demonstrates the life cycle of a fish species called salmon. First of all, every salmon's life is started from its eggs under the reeds and small stones in the upper river, where water flow is moving relatively slow, and it often takes about 5 to 6 months for the fry to get mature enough to come out of its egg. The fry is usually very small, with the length between 3 and 8 centimeters, and it tends to stay in the lower river area for approximately 4 years until it becomes smolt, a stage before fully grown up and usually with body-length between 12 and 15 centimeters. After turning to smolt, the fish will move to open sea and stay in the area for around 5 years in order to become an adult salmon. Finally, the mature salmon will go back to its birthplace, the upper river, to give birth to its next generation.