What is the name of a fish that goes between salt water and fresh water?

A fish that goes between salt water and fresh water is called a diadromous fish.

There are two main types of diadromous fish:

* Anadromous: These fish live in saltwater but migrate to freshwater to spawn. Examples include salmon, shad, and striped bass.

* Catadromous: These fish live in freshwater but migrate to saltwater to spawn. Examples include eels and some species of gobies.