Here is a population management tip for those pondowners to reduce numbers of gizzard shad in states where ice cover occurs. According to fishery research at Cornell University NY gizzard shad become more vulnerable to winter kill when winter water temperatures drop below 39F. Deaths increase as the water temperature decreases toward 33 - 34F during "super cooling" conditions. Super cooling is defined here as water temperatures below the normal winter water temperature of 39F. Some species of fish are more vulnerable to "super cooling" than other species. Trout are the most tolerant of super cooling.
If you use bottom aeration, you can reduce the winter water temperature under the ice from 39F to as low as 34F to sometimes 33F by running the aerator for long periods during winter. To get the lowest water temperatures, place the diffusers in the deepest part of the pond and run the aerator for long periods daily or 24/7.
Link to Reference: http://www.in-fisherman.com/biology/science-of-shad-winterkill/