Freshwater fish
From a general point of view, freshwater fish means that they can live in environments with a salinity of 0.3% of freshwater fish. There are three categories based on the salt concentration in the water: primary freshwater fish, secondary freshwater fish and peripheral freshwater fish. Freshwater fish can also be classified according to their migratory nature.
1. Low-level freshwater fish
Fish that can only live in freshwater throughout their lives. Accounting for 33.1% of the world's total fish, there are about 8,600 species.
2. Secondary freshwater fish
Fish that live in fresh water for most of their lives, occasionally exercising or resting in semi-salt water or sea water. Accounting for 8.1% of the world's total fish, there are about 2,100 species.
3. Peripheral freshwater fish
Fish that rest in seawater or semi-salt water, and whose life history will also live in fresh water, or join the movement in semi-salt water. Including anadromous fish, fish falling into the sea and marine fish that occasionally participate in river life. Accounting for 0.6% of the world's total fish, about 160 species.
4. Classification according to migratory nature
Non-migratory pure freshwater fish: fish that live in fresh water throughout their lives and have no migratory nature.
5. Migratory fish (two-way migratory fish)
During a certain period of time in their survival history, they lived in waters with different salinities such as fresh water and oceans. It can also be divided into fresh water migratory fish and river and sea migratory fish. The life history of the former freshwater fish, including migration, all takes place in fresh water. During their lifetime, the latter passed through resting areas with no common salinity. The border between rivers and seas is where they must pass during their migration.
6. Estuarine fish
Fish that live in fresh and salt water confluence areas and seawater.
</p>
</p>