It is believed by locals here in Indonesia that moray eels hunted primarily by the sense of smell. And thus, most eel-keepers will tell you that if you keep a quantity of small mollies and shrimps in the same aquarium with a moray, the eel will hunt and eat lots of them, but after a few months, the remaining survivor will have their smell "blended" with the aquarium water and sand, and thus the eel will be unable to distinguish their smell anymore.
Does not sounds too logical, but I have an interesting observation. Most of the brackish mollies that I bought last year now have grown big, bigger than the moray (this particular species is the snake moray eel, Uropterygius Micropterus, from Java, Indonesia), and the tiny shrimps also has grown larger than the eel's mouth. The eel are not interested in them whatsoever, but would still eat newly-introduced shrimps and mollies. So the locals might be right
Does not sounds too logical, but I have an interesting observation. Most of the brackish mollies that I bought last year now have grown big, bigger than the moray (this particular species is the snake moray eel, Uropterygius Micropterus, from Java, Indonesia), and the tiny shrimps also has grown larger than the eel's mouth. The eel are not interested in them whatsoever, but would still eat newly-introduced shrimps and mollies. So the locals might be right