Its an odd looking stone but to be honest, I think its a stretch to call this a fish. IMO its really stretching it lol. I guess its like looking in the clouds and seeing a flying horse..
I hope others will post their honest opinions because Im sure you are looking for the truth. I agree it may be some kind of fossilized impression. You may try the American Indian Artifacts section for more experienced answers.
http://forum.treasurenet.com/index.php/board,89.0.html
Keep looking for unusual things in the stream beds. Im sure you will find something if you keep looking.