I put a minnow trap out last night at 8pm. This morning at 9 am I checked it and there were 10 small dead bullhead in it. It was at about 6 feet deep.

Am I right in assuming that they died because there wasn't enough air in the water at that depth? There has been almost no wind over the last week here, and my pond isn't aerated yet.

Just keep doin what you're doin.

I usually only put the trap a foot or two deep if trying to catch bullheads.

Sounds like they went in the trap during the day while there was enough oxygen at that depth then died when the lower water lost its oxygen over night.

Ok if you are trying to kill them. If you want them alive put your trap higher.

Thanks for the explanation.

And yeah, I'm trying to reduce the number of them. I caught and trapped over 60 of them of them over the weekend without much effort. They're all small. A few years ago, they were much larger.