Well we found that the little fish that came in with the feeder fish order at work is a baby bluegill. So my first question is....what do they eat? I gave him a few bloodworms and left him alone and when I came back 6 of the bloodworms had been eaten. (he's on a bare bottom tank) So at least I know he likes those. I work at a pet store so I can get him many different kinds of foods if necessary. He's only about an inch long.
I also looked up some general info on them. It says they prefer water temperatures at 60-75. Should I just leave the water at room temperature then and not get a heater?