I saw something today that seemed a bit unusual (to me anyway). I was at a small lake and saw a large school of bullheads tightly packed together swimming near the surface. This wasn't so unusual, as I see similar schools nearly every time I'm at this lake, and have long been familiar with the fact that bullhead fry form tight schools. However, the schools I am accustomed to seeing are made up of very young bullheads around an inch in length and solid black in color. The ones I saw today were much larger. I would guess around 4 inches. I also was able to see, when some of them were pushed up above the surface by the mass of fish beneath, that they were no longer solid black but had golden bellies like the adults do.
I was really surprised and fascinated to see fish of this size behaving this way and watched them for about 10 minutes. How long do bullheads retain this swarming behavior?

I heard they do that until they are two inches long.

This is a rather common behavior for young bullheads. It is always a neat site so see though when you do come across a group of them.