Once I was fishing, then suddenly flasher started showed all red, fluttering, then solid pretty much all.
Saw my rod tip started to shake. Looked down the ice hole, flash light shown down of course. Saw a big school of big fish. All swimming high speed like a stampede of land animals only this was like a cloud of fish. That lasted like for 10 minutes. It was about 10pm at night. These were all thick bodied fish too. Could've been carp, suckers, or buffaloes. I was on 30' of water depth. The solid line was from top almost all the way to the last foot of bottom. The only other type of fish that I've seen to cover a wide range of depth in large schools to create virtually a solid red line were smelt, shad, white bass, and channel catfish in the river.
I never knew this lake to have had such a large quantity of whatever fish in such a large school. Judging from the speed, they were swimming away from a predator. Now what and how many predatory fish, large enough could be chasing such large fish that are easily into the 20"+ in length.
In certain spots, this lake does have a night aquatic hatch from the bottom to several feet off bottom. However much the signal is, it has usually just a fluttering mess of signals, but hasn't gotten to a solid red line.