I was thinking D.O. would be it too and embarrassingly I haven't been checking it like i should.

However my trout that have plenty of D.O. with inflowing oxygenated well water and they don't feed too much in the morning either. But the bass in my bass pond are hungry morning and evening. Maybe like your hybrids it has something to do with the aggressiveness, competitive nature of a species or their metabolism?

I only have brooks in the trout pond but when I had brooks browns and rainbows they all fed ravinously morning and evening. I have to wonder if competiton may have something to do with that one.

I want to put in a 1/8th H.P. surface aerator in the little 1/10th acre pond next summer and see if it makes any difference.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.