Ice is rarely the problem. The problem is snow on top of ice for longer than 4-6 weeks. It takes several weeks of snow cover for the DO to begin a decline toward a concentration that will stress fish. The clarity of water at freeze up also plays a big part on how long DO will last in dark conditions. Remember as the water first freezes in winter, the DO top to bottom is always at maximum concentrations (12-14ppm) with full saturation at 100%.
In relatively clear water and most everything in a dormant phase at freeze up, it usually takes several weeks (cloudy water) to a couple months (clear water) of compete darkness before the water near the bottom to loose its DO to where fish are forced into shallower water where DO is higher and above 1-2ppm. The deeper the pond the longer the DO will remain high enough in the upper layer for fish survival. DO is lost from the bottom upward. Fish in winter in water 39F are able to survive in a lot lower DO compared to low DO in summer temperatures when the fish's metabolism is higher and requiring significantly more DO for respiration.
Last edited by Bill Cody; 12/29/15 02:52 PM.
