The yellow-headed moray, Gymnothorax Ruepelliae, I've seen up to about 20".
The fimbriated eel, Gymnothorax fimbriatus, I've seen up to about 30". The fimbriated is often sold in common terms as a dark-spotted eel or a yellowhead moray eel, which adds to confusion for the casual LFS shopper.
Yellow-headed eel: