is it a female cherry barb i brought some today and it looks like them
Its Bluefin killifish (Lucinia goodei) one of our North America native killifish.
Mostly likely you have a female bluefin or immature bluefin. Only mature male bluefins has blue dorsal fins.
I wish I still has my bluefins but I moved out and sold all fish. I got mine from www.aquaculturestore.com and sometimes from feeder shrimp tank. You can find bluefins in ghost shrimp tank or plant tank in your lfs, the bluefins are hitchtakers, come in with shipment.