what about some of the smaller eels like Pseudechidna brummeri (white ribbon eel), which may get over 24", but is very slender. There's always the costly Gymnothorax melatremus (golden dwarf moray) as well. Echidna nebulosa, Gymnomuraena zebra, Echidna catenata (atlantic) can also be recommended, though they may outgrow their enclosure over the years. None of these will take down fish larger than a small anthias, though they may try.