Yeah I would go with a bullhead too. I have a breeding pair of Yellow Bullheads in a 700 gallon pond with some turtles and Fathead minnows. I caught mine in a stream near my house.
Mine are active when it's warm too. I live in PA so when it gets cold I don't see them that much. They do come out when it's feeding time and they love any type of koi food, worms, prawns or dough balls.