The catfish family contains around 2,000 members, which include some of the more unusual aquarium attractions: certain species swim upside down; some can maneuver on land; and others can emit sound or use electricity to kill. All are from the Americas, Africa, and Asia and share the common characteristic of bottom-dwelling. Many are surprisingly gregarious and enjoy being kept in numbers, but some catfish are nocturnal, and their regular activities often go unnoticed. Catfishes are identifiable by the barbels around their mouths, which allow them to locate food in the dark. Instead of scales, the skin may be naked or covered with bony plates, or scutes. They often use oxygen that is gulped at the surface and extracted in the gut. Usually omnivorous, some species are herbivorous and are useful in controlling algae. Catfishes spawn in several ways, including egg-depositing and bubble nest building.