I used to assume the fungus issues associated with cold water was food / fatty acid profile related. After running trials with Bluegill in cages and having heavy losses that involved fungus, I am thinking something else is at least an overriding factor. The key trial had several diets, each represented by 2 cages full of fish in four ponds so each diet was fed to eight cages and each pond had all diet represented. Diets were chosen to have a range of fatty acid profiles following theory that is the cause. Two ponds had light mortality as in the 5 to 10% range, another had about 40% mortality, and another had more than 80% mortality. There was no obvious pattern within ponds as a function of diet. Water quality was not an issue as that was checked regularly even with ice and snow cover over ice.
My assumption at this point is the fungus is secondary. Results of that particular trial completely destroyed or effort to compare the effects of winter feeding as function of diet.
I really do not like overwintering Bluegill in ponds that were fed heavy the growing season before as it can be replicated even when cages not involved.
