The encyclopedia was very vague on the definition as usual. But my bad I forgot about mudskippers, killies, and such that do undergo hibernation. They will dig into the mud or climb into crevises in branches and go into a true hibernation.
Koi and goldfish however do not "hibernate" as they are active all winter (just reduced activity level). Hibernation is a very precise defination that is generally used to broadly in common usage. It has a very precise scientific definition that is constantly being argued about what species fits into the box. The change in body chemistry is actually very severe and there many different degrees of hibernation.
That will teach me to type and try to do the required harassment training at the same time. Waiting for the timed pages (cause it's got to last two hours to be legal) webpage to load left lots of time for me to do other things.