The feeding habits as described, reminded me of a documentary I saw about deep water fish of the Amazon river. In one scene a huge bait fish was dropped into the water and a diver accompanied it to the bottom of a deep portion of the river (a couple hundred feet as I remember). The swarm of eel like fish surrounding the dead bait was impressive but when the small fish became too aggressive both the diver and fish were raised back to the surface. Top side, the bait fish's skin was relatively intact but the innards were full of the little bottom feeders that refused to leave the bait, even when exposed to the air.

I wonder if these critters were a fresh water version of the hag fish? Probably not since it would be fresh water versus salt varieties of fish. I also wonder if the slime aides in defense or whether it helps the fish invade the orifices of the dead fish it feeds on?