Ive kept eels out of the nepean with geophagus and severums,with out any dramas(it was a 4x2x2)The eeel usually only came out at night or dusk,but be prepeared to make the tank like fort knox as eels can get out of almost anything.My guy used to escape when the mood tok him,and theses nothing worse than being woken up by a 4 foot eel sliding off your pillow and under the blankets(the tank was right next to my bed)makes you almost want to give away all your fish its that frightning