I used to have an Anguilla Bicolor (Indonesian eel) for years, it was a very nice pet, very intelligent, I trained it to take all kinds of food live or processed, to the point of hand-feeding. But then it grown to be very large, and I donated it to a friend who has a larger aquarium.
Here is a nice clip of my Anguila Bicolor.
Nowadays I keep a small Echidna Rhodochilus (white-cheeked moray eel) in low-end/semi-brackish aquarium (it's practically freshwater with 1/4 part seawater, actual seawater I took from the beach, not "seawater" made of artificial salts).
Echidna Rhodochilus is a very cute eel, and it stays small (maximum length 35 cm). If you could provide a nice low-end/semi-brackish environment for it, it will do fine. Here is a nice clip of my Echidna.