And you have this trigger in your 55G tank? Not a very good tank size for a type of fish that gets to be about a foot. Also, i would suggest moving rocks around to get to him. If you can't get him out at all, even at night when he's most vulnerable, then clearly there's no other alternative to getting him out. Never heard of a fish trap either.. maybe lure him out with food and then have a net ready, and when he comes to the food, just bag him.