I have a fire eel, tire track eel, and albino senegal bichir.
The tire track eel is big (and growing) and territorial. NEVER leaves her cave.
The fire eel moves around and is very friendly. He even swims to the surface of the water to greet me. I've had him longer than the tire track but he hasn't grown at ALL. The tire track eel has close to doubled in mass.
The bichir is nosy and will bite anything that's either dead or very slow moving like ground worms. I've never seen him attack any of the tank mates except my very small flounder which he killed.
The tire track eel will beat up the fire eel on sight with no hesitation.
She will scare off the bichir, trinidad pleco, candy striped pleco and sometimes even the black ghost if they hang out near her cave for too long.
But she has this very strange bond with my gold albino bristle nose pleco and (since the day I added the pleco) she actually allows him to go completely inside the wood w/ her. It's helarious... she just observes him very carefully.
Today I added an angel fish... VERY STOKED!