Very common I must say. But nevertheless nice ... once it's acclimated in your tank. Try target feeding and you'd be amaze by the amounts of opened mouths .. feed them little tiny pieces of meaty food or mysis provided that you don't have any "annoying" fish around.
What I would normally do is .... use a pair of tweezers and carefully hand feed the tiny mouths and you'd be amazed to notice them 'lil mouths swallowing the foods being offered .. in a few minutes ..