Ditto, to what xDave said.
They're not like normal fish. They'll look like they're having trouble breathing, but it's perfectly normal. If it's slow breathing, they're fine...if its fast, rapid breathing, there might be a problem.
What species of Moray are we talkin' about, here and what are the specs of the tank? (water specs, as well as tankmates).
I just got a little snowflake eel. I was reading some of the threads about them...normal breathing is through the mouth....one said it looks kinda like they're swallowing all the time, but if they are stressed it looks like they're hyper ventalating. :notsure:
I guess you could say it looks like they are swallowing by the way their gills puff out. Once in a while my snowflake will yawn, he will open his mouth really wide just like a yawn which I guess it could be because yawning is to get more air to the lungs or gills in a fishes case.