Not many eels will fit in a 29. Maybe look for an eel-like fish. What about an engineer goby? I think it would eventually also outgrow a 29, but at least maxes out at 12". I kept a green wolf eel in a 55 for many years (but again, not good for a 29). I'll think on it some more. Besides expensive dwarf eel already mentioned, I don't think you will be able to do a moray or any other eel.