Interesting topic, and one of the few that I actually have "some" experience with. I think one of the major factors involved here is the fish density of your pond and also the pond's age and amount of nutrient present. The larger the b.o.d. (biological oxygen demand) then the greater chance of some winterkill.As an advantage, colder water holds more oxygen than warm water.
I only have experience with trout, where a warm water refuge is not really an issue for survival so I cannot comment on the pros, cons of that.
Last winter I had 196 days of ice on my pond. Maximum ice thickness was over 30". I did not aerate and had no winterkill at all. This is a newer pond and fairly low density. I did remove most snow cover quickly and routinely.
The one thing I found that did suprise me was the amount of light penetration through very thick ice. Dropping the underwater camera down even with only 6" of snow cover showed almost complete darkness, yet where I kept the snow off was very well illuminated all the way to bottom even with near 3 foot ice thickness. For my purposes, snow removal is key to over wintering trout and not aeration.
Oh, and for you Texans, air temps this morning here were -37c. Tonight when I got home we were at -4c. Gotta like the Rocky Mountains.
Wood
