i USED to have a lionfish, got rid of it tho, so i could get baby clowns,
my lion was roughly 5" long, and i used to feed it hole cockles once a day, it would only eat 1, even tho i'd feed twice a day because of my puffer and trigger, but yeh, it would eat once a day with one whole cockle, and it had a nice plumb belly, seemed happy and healthy
oh yes, and it was a volitans lionfish