^ I agree. I had a madtom, and thought it was a big channel. it looked the same as channels ive kept before, until it started getting splotchy looking. but channels do grow very fast, and imo are very fun to watch grow. good luck!
That doesnt sounds like normal for bullheads. Your bullhead's probably just regular madtom. I have raised bullheads in the past and I can tell you that bullheads aint slow growers either.