In the wild, saltwater fish will swim. But if they catch fish into fresh water, will they survive?
Some fish can live in both salt and fresh water. They are collectively referred to as euryhaline fish . However, most fish can only live in one of two environments (saltwater or freshwater), depending on their tolerance to salinity.
According to the US NBII biology classification table, the broad salt fish group are highly adaptable species. They can migrate back and forth between salt water as in the sea and fresh water such as certain ponds, lakes, rivers and streams.
The group of broad-salted fish is divided into two main types: upstream to spawn (sea fish) and migrate to the sea to spawn (river fish).
Salmon is classified as a group of broad-salted fish.
Unlike the broad salt group, most fish can only tolerate small fluctuations in salinity and are extremely sensitive to any changes in salt concentration in their habitat. 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 the narrow salt fish group, but can only exist in salt water.
In fact, freshwater fish will usually not be able to survive if the salt concentration in the habitat increases to more than 0.05% , according to Table NBII.
When moving, even large saltwater fish need time for their bodies to adapt to the salt concentrations different from their familiar habitats. By combining the salt concentrations of the habitats with their different life stages, salted fish can balance the desired concentration in their bodies with their surroundings.