I caught that fish at 120 skill Ice dungeon river west of the arctic ogre lord although I don't think it is location specific as I have pulled up 2 so far in different areas of the river. I had no bait so no bait was used it took approximately 10-12 hours total fishing time spread out over a week or so to get those 2 so they are not going to just jump in your backpack like pie fish. Very time consuming process catching these elusive fish. So yes they do exist I had not pulled one prior to legendary fisher either and that was my primary source of dungeon fish pre 120. Hope that helps and good fishing.
The Albatross/Lord Aphid LS