JD is correct. "Prehistoric fish" generally refers to the gars and the bowfin because they have a physostomous swimbladder which precedes the physoclistous swimbladder of the "modern" fishes.

Just an fyi:
We date the origins of almost all of the fishes that we have today to roughly 400 million years ago. The lampreys origins may date back 450 million years and the Hagfishes may date back 550 million years ago. So I guess in this aspect we could call them all prehistoric. lol