I have a female green wolf eel. As was already mentioned they get upto around 18 inches. She is fairly avtive in my tank. When you go around the tank, she will come out(she thinks she'll be fed). Also thay will follow you around the tank.
I have a zebra moray thats about 3 ft long so this would be a big no no
Morays that would probably work include Chestnut/Viper Moray,Chainlink Moray,Snowflake Moray, Banded Moray,Whitelip Moray(Not whitemouth moray),Goldentail Moray (my favorite small eel),Richardson's Moray and thats about it
Eels that get way to big include Zebra,Green,Dragon,Whitemouth