My friend and I have had terrible trouble having two porky puffers in the same tank. She has a 240 and we tried to put one puff from our office tank in her big tank. They fought like crazy, round and round, by the mouth fighting -- until we just had to take the "office" puff back out. I think the eel will okay with it, but unless you had two at the same time, I'd be VERY careful.