11.15.08
OXYGEN-DEPRIVED FISH
Too many fish die of no apparent reason every spring. A veterinarian friend of mine has a theory about this fish loss. I want to share it with you.
We all know that it is important to maintain a “hole in the ice” covering during winter, for gas exchange. Many of you will do this with a bubbler (aerator) and others will keep the ice open with a floating de-icer. Both are excellent in keeping a hole open for the gas exchange while your fish are dormant in winter.
What you may not know is that both will create a condition of vertical water flow that draws the water (and oxygen) from surrounding areas in the pond. Unless a fish is lucky enough to be “sleeping” right below one of these gizmos, he is likely to run out of oxygen before the thaw. Dr. Tepper, DVM explained the ice-cube theory, wherein ice floats and warmer water sinks. So, as a de-icer is heating the water, it is sinking and the colder water is surfacing, to be heated, and to sink down again. This cycle will draw oxygen from the cold water in outside areas, but since the up-down flow is limited, none will be replaced. Likewise, the bubbler will create a column of bubbles to the surface, drawing from surrounding areas. This is not a problem until ice is covering the rest of the pond. At that time, no more oxygen is entering the water through surface gas exchange, anywhere but right above the bubbler.
What’s the answer? You can use the de-icer or the bubbler, but should be mindful of placement. Place the device directly over where your fish will be during their dormancy. If you have a large amount of fish that can’t all fit in one deeper area, then you will need to set up a gentle horizontal water flow to carry oxygen throughout the pond.
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