Pleco Ceramics Pleco Cave Natural Large is made of clay fired at high temperatures. This makes them absolutely safe for people, aquarium fish and pets. These Pleco Cave's are helpful in breeding and in reducing aggression among fish. They look very natural and realistic inside the tank. Just flush the tube in running water before use. Can be used for most of fish and shrimp species. Ideal for Bristlenose and other Plecos. This cave has only one opening.