The diagram illustrates the life cycle of a large fish species, the salmon.
Overall, salmon pass through three main stages of development, beginning as eggs in the upper river, then growing in the lower river and open sea, before finally returning to the river to reproduce. During this cycle, they increase greatly in size and live in different water environments.
At the first stage, adult salmon lay their eggs in the upper river, where the water moves slowly. The eggs are placed among reeds and small stones for protection. After approximately 5 to 6 months, the eggs hatch and young salmon, known as fry, emerge. At this point, they are very small, measuring around 3 to 8 cm in length.
Next, the fry move downstream to the lower river, where the water flows faster. They remain there for about 4 years and grow into smolt, reaching a length of 12 to 15 cm. After that, they migrate to the open sea.
In the final stage, the smolt spend approximately 5 years in the open sea, where they develop into adult salmon. By this time, they are much larger, measuring about 70 to 76 cm. The mature salmon then swim back to the upper river to lay eggs, and the cycle begins again.