I'd agree it is to small for any species of Asain Spiny Eel or any other. You may want to try a Kuhli Loach? They are 'Eel' shaped and would be able to live in that size tank.
ryan has summed it up for you in one mate kuhli loach will do well and like he said mate your other fish could soon become food if you got a fire/tryetrack eel