Since the pond in WI has year round aeration and the old timer big bass showed resultant signs of "severe Columnaris growth, ulcers, and etc. it is possible or likely that too much aeration during a cold long Wisconsin winter produced too much cooling of the water below the standard 39F and this stressed the old bass too much, to the point the secondary infections colonized the stressed fish and eventually killed them.
Others here have seen evidence of LMB being stressed due to chilling the water too much during harsh winters. Consensus here currently is, it is best to move diffusers into shallower water for winter aeration to avoid reducing the entire water column temperature of the whole pond to the 33F-34F range. Some fish species tolerate water temps below 39F better than others. Oldest fish may be more vulnerable to the really low temps more than others, depending on the species and length of time the water is "supper chilled".
Thanks Bill. I do move 2 of the diffusers into about 3ft of water, and about 20ft apart from each other (in both ponds)... Have to keep a decent size hole open for the Pekin and other ducks. All the other diffusers are shut down to minimize the cooling effect of rolling open water.
An added benefit of moving the aerators is to have open water at the shore, so that the deer don't walk out to get a drink and fall into deep water... They can just walk to the shoreline and drink safely.
As for the LMB... I agree it was likely stress from the winter, stress from being old, pre-spawn stress, etc... Spring is the hardest time for fish, and LMB aren't the best at coping.
If I remember correctly, the ice-out on this pond that year was rapid... It was like 10" on on a Sunday (when we caught those perch on the filet board) and completely gone by Tuesday! That big of a temperature swing that fast is enough to temporarily shut down a lot of fish's immune systems.... And there's a lot of opportunistic fungus and bacteria just waiting for this.
The whole thing reminds me of scenarios my Fish Health professor used to come up with for questions on tests and finals.
