The movie Catfish brought that word as a descriptive into the general language where it has found a place in the Urban Dictionary.  IMDb quotes the character, Vince Pierce from the movie as he describes the term:

“Vince Pierce: They used to tank cod from Alaska all the way to China. They’d keep them in vats in the ship. By the time the codfish reached China, the flesh was mush and tasteless. So this guy came up with the idea that if you put these cods in these big vats, put some catfish in with them and the catfish will keep the cod agile. And there are those people who are catfish in life. And they keep you on your toes. They keep you guessing, they keep you thinking, they keep you fresh. And I thank god for the catfish because we would be droll, boring and dull if we…