There are at least two types of systems that increase oxygen, bottled compressed oxygen or a system like the Aqua Innovation, which electronically splits the oxygen molecules from the water molecule, the hydrogen evaporates and the nano oxygen bubbles work to saturate the water. Both systems work best if you don’t exchange the water to often. But by not changing the water some slight build up of fish releases toxins occur, but for the most part this isn’t a big concern. The AquaInnovation system is widely available, it can also be purchased through the mnbf.org website. I use one in my boat and have been happy with it. (Most new boats are coming with this system available as an option)
If is very difficult to determine mortality of fish unless of course you keep them out of water and let them die. But, anytime we discuss mortality we need to factor in natural mortality. Just as we see people of all different ages dying, so do fish. Often trying to figure out what combination of stressors lead to a particular fish dying in the livewell will never be known. Low oxygen levels, high temperatures, poor water quality are factors, but so its hooking, handling, and the fishe’s health.
I had the opportunity to work with the fish at the Classic for a couple of years; we did see differences in temp. and oxygen levels between different types of boat aeration systems. But the biggest variable prior to weigh-in was the angler’s knowledge of how to properly operate the livewell aeration systems. Some added the ice we provided, and kept the dials to manual on, and constant exchange. Others used the timers and never exchanged water. My observation is that the anglers who were familiar with the equipment did a better job keeping bass alive.