When I was a kid growing up in Alaska I met a family that was very active in the local aquarium club. Odd to think how things have changed as I haven't heard of anything like an aquarium club for decades but that's the way it was then.
Their name was Baleau IIRC and I think it was one of the parents that applied for and rec'd a permit from F&G to catch and keep a local fish known to be able to freeze, thaw back out and survive the ordeal. As I recall it was not an attractive fish by my Pineapple Swordtail standards of the time and I couldn't understand why anyone might want to keep one. They had it for several years and thawed it back to life in spring multiple times as I understood it.
There was a debate at the time about the existence of ice worms as well. Never paid much attention to that one.
That sure sounds like the Alaska Blackfish! It's not for the interior decorator fish crowd for sure; looks like the Incredible Hulk version of an Umbra mudminnow. I personally think they are very interesting...but I feel the same way about mudminnows, so...
coldwater fish such as lake trout and burbot travel extremely shallow in the winter since the whole water column is cold and they are no longer limited to staying below the thermocline. I target brook trout in 2-3 feet of water in winter. I think the water temperature is more dictated by vegetation and bottom composition during the winter than it is by depth. I have caught perch in 4 feet of water in vegetation at the start of winter but they transition to deeper water as the weeds die off shallow.
I'm not sure I see how those factors would affect water temperature. I agree about the fish moving deeper as winter progresses but I suspect it might be because of possible lower oxygen levels as the dead vegetation decays in the shallows.
The temperature difference between the shallow and deep water is much less pronounced in winter, when it's only a couple of degrees, as opposed to summer when it can be much greater.
We have good luck catching pike on deadbaits set right on the bottom in reasonably shallow water in late winter, close to ice-out. I think they move for brief periods into those areas looking for fish that have succumbed to low oxygen levels, because we rarely catch pike by "dead-sticking" at other times of the year. They also seem to fight much less when hooked then, which adds to the supposition IMHO that they are nearing their limits in terms of dissolved oxygen levels.
