Got to thinking.....you don't have that many pups do you Mike? I think that you gracefully sent the bulk my way. The animal will tell you if it is not getting enough oxygen by floating to the top. Not once in a while or one or two of them occasionally, but most of them. This is them communicating to you. Fish do this more than the Axies. In the bait business, I run pure oxygen in my holding tanks, to what is called "keeping the fish down". If they are down then there is enough oxygen. If they are at the surface then there is trouble. The reason I think it is more prevalent in fish is because the gills are internal where as the gills of an Axie are external. Only a guess on the gill thought.