Just about any eel will do fine, i know the last person said nothin under 1000 gallons but its rare that they get over 7 feet in captivity, knowing this and knowing many eels like to curl up so they can protect their whole body, i would chose a chainlink, zebra, snowflake (smaller eel), or a banded, green morays get rather thick and that could be a problem in a 55.oh blue ribbon eels are sweet, take a look at those you might like them.