It sounds like you're looking for a technical answer. All I can say
is that as the water cools (gradually), it slows their metabolism.
They sink to the bottom (is colder water that more dense?), and their
activity level, appetite, colour and respiration are reduced.
Shock from a sudden drop in temperature will affect fish differently,
mostly depending on their mass. Little fish die and larger fish are
noticeably 'uncomfortable'. When I had a new employee fill a tank
with ice-cold water, the cichlids all parked at the bottom and faced
the front of the tank. If I read their expression correctly, they
were not amused.
ps: When water is a few degrees too cold, you should increase it
slowly to not shock them. If the water is very cold (ie: more than
8F), the advice is to increase the temperature quickly. I don't know
why but this is what I've successfully followed for many years.
NetMax
On Jan 27, 10:44 pm, "pH7, Aquarium Ninja" <
p...@aquariumninja.com>
wrote: