ok, your pond has to be deep enough to stratify, i. e. cool water on the bottom warm water on the top with a boundary layer. The two levels don't mix so the bottom layer becomes anoxic, which dead algae on the bottom would facilitate.
When the top layer cools it breaks up the stratification and the two layers mix with the anoxic layer reducing the oxygen concentration to potentially lethal levels. The centrarchids are more susceptible to low oxygen levels than catfish so you can get differential mortality, depending on the level dissolved oxygen drops to.
NO AMNESTY!
in order for democrats, liberals, progressives et al to continue their illogical belief systems they have to pretend not to know a lot of things; by pretending "not to know" there is no guilt, no actual connection to conscience. Denial of truth allows easier trespass.