Mystery Fish

I think he hitchhiked into my tank as an egg, attached to a plant. When I first noticed him, he was very tiny. Now, he's about an inch long. I thought he was a cherry barb fry at first, but the coloring is very different. The red is only at the base of his tail, and it's a different red - less orange - than a cherry barb's.

Update: this fish has been revealed as a bluefin killiefish, Lucania goodei. It's a scrappy little thing, chasing shrimp and fish larger than it is. So far, it hasn't done any physical damage. Still, it's not a critter I'd have chosen for my tank. Anyone in the Mid-Hudson Valley want a bluefin killie?