Haha, he sure is an adorable guy xD I'll look around and see if I can find a name for him(what species he is) ;)
Never had or thought about eels myself, but I hear they to like to escape as previously mentioned so be sure you have a tight lid. Also, it'd surprise you what fish can fit where in your tank so if your really worried check every crevice and cave in your tank and you'll probably find him, permitted he hasn't escaped of course.
EDIT: Alright, looks like you've got yourself a Rope Fish there, I thought that might be the case. Do some googling, but matching what I've found to your picture it looks exactly like it. However, your the only one that can tell for sure as you know what he really looks like xD
Anyway, if this is that case then he's not fully grown, they can get over a foot from what I've read and require large aquariums.....like 50+ gallons I think. Again, I'm taking this only from what I've read, anyone else more experienced is more then welcome to chime in xD