After growing in the ocean for about 4 years, salmon will migrate to the freshwater river where it was born, regardless of the long distance and even Wan Li. Because of the large number of salmon, and their trip is one-way (usually they die in rivers after spawning), the migration will bring back a lot of materials and energy absorbed by them in the ocean to the inland, and feed many creatures in the inland. For example, the grizzly bear in North America is an animal that relies heavily on salmon. There are more than 200 species in the salmon migration area in North America who rely on salmon as their food, and 80% of the nitrogen in the forests in this area is made of salmon. Therefore, the Great Migration realized the circulation of matter and energy in nature.

The reason why salmon migrate is because salmon eggs can only survive in fresh water. Of course, there should be other reasons. Salmon migrate to rivers, and their kidneys and other organs have to adapt to the sudden lack of salt because of sudden contact with fresh water, which is a life-and-death test for them. Under normal circumstances, they will stop eating or even drinking water after entering the river. They struggle to run upstream, relying on the energy stored in their bodies. When salmon swim upstream in rivers, they often encounter many high-drop currents, such as waterfalls. At this time, salmon will jump over, which is the ability that salmon evolved after 6 million years. Generally, Pacific salmon will die after migrating and spawning, but Atlantic salmon will not. They migrate and spawn year after year. But the corroded bodies of Pacific salmon nourish the rivers and provide enough food for their growing children.

That's why the little mahi fish grew up eating mom's meat.