The diagram depicts how a species of large fish called salmon continues to evolve during its life span. It can be observed that the salmon starts its life cycle from the upper river that is slow moving and ends its life cycle in the open sea after approximately 5 years.
To begin with, the salmon starts its life cycle in the upper river and stays there for approximately 5-6 months. Initially salmons are in the form of eggs that are present under the small stones. They grow to be ‘fry’ fish that are approximately 3-8cm in length. Further, they reach the lower fast flowing river and stay there for approximately 4 years.
In the lower river they grow to be smolt and have a length of 12-15 cm which is considerably larger than when they started from the upper river. These salmons are then found in the open sea where they have a lifespan of about 5 years and they grow to be adult salmons that have a length of 70-76cm.
The overall lifespan of a salmon is approximately 9 and a half months where it goes from its initial stage as an egg and a fry fish in the upper river to an adult salmon in the open sea.