scs0 wrote:

It's a commonly accepted rule that fish need to slowly adjust to
changes in water temperature and this is one of the reasons why bagged
fish are supposed to float for a while before being introduced into a
new body of water. I'm starting to think that this temperature
adjustment rule is a whole lot of bunk.
....
Does it have to do with the fact that a fish can return to water that
it's adjusted to if it finds a new pocket of water that's too
uncomfortable?

I don't know that anybody can really answer that question. The same problem
occurs with species of fish that are caught at great depth. In the
aquarium trade there are African cichlids that are caught at 120' or
deeper, that really need to be "decompressed" as they're brought to the
surface (otherwise they develop swim bladder problems), yet these same fish
are known to come to the surface on their own.

I would think it comes down mostly to the fact that the fish know when they
are approaching the limits of the temperature or pressure change that they
can handle (it probably hurts), but we can't tell the point at which the
change is stressing them too much.
--
derek