I have a TT with my 2 Senegels they've been together for a hand-full of months now w/out any major issue. The TT stands up for himself if the Bichir's get to nosy. depending what type/size poly's you have and the dynamics of your tank I would think they will co-habitate just fine. If the tank is fairly mellow I'de suggest the fire eels, if it's abit more on the aggressive side a TT might fit the bill better. Most the smaller species will stay small enough I would have concern about predation. Key I think would be haveing a few hideing spots only the eel can get to. I've been succeful for a few months now w/ my guys. But I've seen my poly's deathroll worms one at each end breaking them in half 'n get nightmares about this happening to my eel. So in the long run i think it will really depend on the poly's aggression levels themselves.