Well when they are small they can usualy find enough to eat, scraps of food or pods or what ever is on the rocks, but as an adult they have to be target fed with peices of fish/muscles/clams etc, but you have to be sure to put it infront of them as they may not find it (slow/poor vision etc), so in larger systems it can be difficult to get the food to them. Though that is depending on the Cowrie, some wont eat fish/clam/muscles and feed only on sponges and soft corals... it really depends.