Unless you are aerating from the bottom of a 20' depth area, the water down there should generally be not used by any fish. I may be wrong, but I think without aeration at those depths, the water down there does not have adequate dissolved oxygen. .
That is the conclusion most people make. However, it only applies in summer. For a large part of the year (cooler period) the water has turned over and deep water has O2. In winter the deep water has both O2 and is warmer than surface waters. The fish relate to structure in deep water and move up and down on the structure for temp and feeding purposes. In huge lakes/reservoirs there can be deep water that never turns over and reoxygenates.
.gif)
