Can brackish water fish live in freshwater?
Depends on the fish. The molly (Poecilia sphenops and Poecilia velifera) can live in either fresh, brackish or saltwater (marine environment). It is one of the few that can do this. Many people cycle their saltwater tanks with mollies because they can be switched back and forth from salt to fresh and fresh to salt if you know what you are doing and do it slowly. They can spawn and deliver in any of the three environments. Some fish spawn in fresh water but the young fish swim into salt water to mature (salmon) and then return to the fresh water place where they were hatched to spawn again. Some fish spawn in salt water and then the fry swim into brackish water to live and grow to maturity before returning to salt water to spawn. So, yes, depending on the fish.
