Drop in one at a time, make sure he sees them. While most will go bonkers you will get the occasional bum that just won't hunt. If you have other fish like triggers, puffers; you may need to target feed and use a feeding stick or net to keep the others away. They wont live long enough if they are not eaten right away to cause any damage. Keep an eye and if he diesn't take to it, remove it, they usually grab it before it hits the substrate. Make sure they are not too big, even though they can handle them, sometimes a captive gets a little intimidated until they get their confodence back.