A crayfish is the same thing as a crawfish - where you are from determines which name you use. (Just like how people say soda, pop, coke, soda pop, etc.) People in the Northern part of the U.S. say crayfish, whereas people in the Southern U.S. say crawfish - and some people say crawdad. This is important to note because if you say crayfish in Louisiana, someone is going to make fun of you.