Saltwater fish can live in fresh water?

Some fish can live in both saltwater and fresh water. They are collectively referred to as salted fish (euryhaline fish). However, most fish can only live in one of two environments (saltwater or freshwater), depending on the salt tolerance of the body.

According to the NBII biology classification table of the US, the group of large salted fish are highly adaptable species. They can migrate back and forth between saltwater such as sea and freshwater such as certain ponds, lakes and rivers.

Goldfish can only survive in fresh water.

The wide salt fish group is divided into 2 main types: river upstream (sea fish) and migration to the sea to breed (river fish). The first type is fish that are born in fresh water but spend most of their lives at sea and only return to fresh water to breed. This category includes salmon, herring, sturgeon, mezzanine and bass.

In contrast, the second type usually lives in freshwater areas and migrates only to saline water to give birth. The North American eel species belongs to this subgroup, according to the US Department of Seafood and Fisheries.

Unlike large salt fish groups, most fishes can only tolerate small fluctuations in salinity and are extremely sensitive to any changes in salt concentrations in their habitats. These species are collectively referred to as stenohaline fish. Goldfish belong to this group and can only live in freshwater environments. In contrast, tuna - also a member of a narrow salt group, can only survive in saltwater.

In fact, freshwater fish will often not be able to survive if the salt concentration in the habitat increases by more than 0.05%, according to the NBII table.

When migrating, even fish species in the broad salt group need time for the body to adapt to different salt concentrations compared to their familiar habitat. By combining salt concentrations of habitats with each of their different life stages, salted fish can balance the desired concentration in their bodies with the surrounding environment.