I'd like to add my 2 cents as well, but not in regards to Opening Day. It has to do with closed season for Trout during summertime and use of downriggers and/or leadcore at certain lakes.

Pulling a large fish from the depths, where water temps could vary by as much as 30 degrees compared to surface temps, would certainly be quite harmful, if not fatal to this species. Some lakes have a very good DO ratio at depths below the thermocline, where the water is cool enough for trout to survive a hot summer.

Not only that the fish is exposed to stress, by means of hooking, but it has to reach the surface in order to be released, and they could easily go into shock, and most of them do.

The temperature differential seems to be the major concern. Not sure about the pressure difference, or if that may affect the fish. But one thing is for sure: pulling a trout from 55F water, to 75-80F water in a matter of a few minutes, will indeed cause major damage.

I don't know a heck of a lot about this fine species, but all of the above make perfect sense, IMHO.