When I see sunfish (Bluegill, Redear, Largemouth Bass and Spotted Bass) spawn deep they have a combination of factors that allow it. Good lighting and temperature with adequate oxygen above the thermocline. Something that forces it is a shortage of quality nesting habitat in in shallow water like frequently found with quarries with mostly sheer walls. Most instances I have seen the extreme depths has both allowing and forcing going on.


Aquaculture
Cooperative Research / Extension
Lincoln University of Missouri