Channel catfish will reproduce to populate offspring in a small pond - saw it happen several times.
Bullheads can be pretty prolific. They easily enter baited wire mesh traps. Look for the larger sized traps or build your own trap from plastic netting on a PVC frame. Abundant bullheads can as you now see will make the water turbid. Turbid water minimizes algae and submerged plant growth that will return when the water becomes clearer as bullhead density is noticeably reduced.
I do think SMB would help reduce BH numbers. How much is unknown. So with some manual fish trapping and SMB predation you could significantly reduce BH density. If you try and add some SMB IMO it would be best to also add a few yellow perch 4"-6" sizes to help them survive competition from BH. Also the SMB stockers should be larger size to best compete and survive with dense BH numbers that are currently overpopulated and have most all natural foods consumed. When the BH density becomes lower the SMB and YP might increase in numbers. If a low oxygen concentration (DO) happens again the SMB will die and YP likely survive. If that happens then try some pike to control BH and YP. Pike(NP), YP, and BH tolerate low DO.
This place makes very good fish traps for smaller fish. I like their cylinder traps. The other traps should have a more shallow area of flat pond bottom to effectively "fish"" the box and barrel style traps. When choosing / buying be sure the trap opening (funnel or throat) is large enough for your size of bullhead to enter the trap. If you contact them, they can build you a trap with a special larger trap opening or wire mesh for catching bullheads.
https://ktraps.com/pages/about-our-trapsThe Z trap also works very good at catching fish. It 'fishes' best on an area of fairly flat bottom.
https://www.reeltexasoutdoors.com/p...ream-perch-sunfish-pinfish-bullhead-trap
