Water temperature is probably the main thing to control. If you can keep it in the 70 degree range the water can hold a lot more dissolved oxygen. My aerator has a recirculation timer so it keeps reusing the same water so you wouldn't loose too much of your cooler temperature. Just using the recirculation feature in my boat last summer I didn't loose many fish thru the hottest part of the summer. I still prefer to ice them before cleaning. That way they're not a bloody mess and I can eat and take a short nap before running down to the cleaning station.