What is your water clarity like and how much, by percentage, of your water is covered by rooted vegetation? The reason I ask, is that the best predator, by far, that I know of for black bullhead is the largemouth bass. If you have sufficient opportunity for sight predators like LMB you will see your bullhead population diminish significantly over time. If you have too much vegetation, or poor visibility, or low density of predators, then the bullhead will likely continue to thrive.
