Ted has more knowledge about this subject in his little pinkie than I'll know in my whole life, but I've seen situation in my ponds where the environment within the border aquatic vegetation were significantly different than in the open water. Presumably this was because of plant respiration and plant death caused by a sudden change in water temps, light availability, etc. It appeared to me that the smaller fish were essentially "trapped" in these low DO zones, whereas the larger fish that were beyond the immediate peripheral vegetation escaped harm.

Holding a redear sunfish is like running with scissors.