Just remember one thing. All crabs are opportunistic feeders. So they will eat anything. Keep them fed, and they will stay away from anything else in the tank. Keep him hungry, and any small fish, slow fish, snails, and other crabs/shrimp will be on his very broad dinner menu. They really eat algae and detritus and pick decaying things off of rocks, but in the event that your tank lacks in this.. you can just cut up small pieces of table shrimp, and they will gladly pick at and eat that. Even chopped up silverside would work. Even so, the emerald crabs are my favorite. So good choice!