The term batfish is used for many different fishes, but predominantly for the members of the families Ogcocephalidae and Ephippidae (especially for the species belonging to the genus Platax). The term batfish is also occasionally used for species belonging to other families.
The family Ephippidae belongs to the order Perciformes and contains 20 described species divided into 7 different genera. In addition to batfish they are also referred to as spadefish. Some of the Ephippidae species have been successfully kept by aquarists.
Ephippidae species lives in the Atlantic, Pacific Ocean and Indian Ocean. Most of the species are marine creatures but some batfishes can be found in brackish environments. Some species are appreciated sport fishes due to their strength and resilience, e.g. the Atlantic spadefish (Chaetodipterus faber) which inhabits the Caribbean Sea and the south-eastern coast of the United States. Overfishing of certain Ephippidae species might cause problems for coral reefs since they are known to consume seaweed that other herbivore fish refuse to eat.
Ephippidae fishes are deep-bodied and laterally compressed with small mouths. They are omnivores and feed chiefly on algae and small invertebrates. All species are believed to be pelagic spawners that do not guard their offspring but more research is necessary before we can know for sure.
As mentioned above, the term batfish is chiefly used for the members of the genus Platax. Juvenile Platax species are easy to keep in marine aquariums, but you should keep in mind that they will grow fast. Always find out the maximal size of the species before you make a purchase. Platax fishes are reef dwellers with spade-shaped, laterally compressed bodies. They look a bit similar to marine angelfish, but they are not close relatives. Dorsal and anal fins are symmetrically triangular and the silvery body is decorated with brown or black bands and yellow areas. The eyes can be hard to spot since they tend to be placed in one of the bands.
The family Ogcocephalidae contains 68 known species of fish divided into 10 different genera. Ogcocephalidae is a member of the order Lophiiformes; the order of the anglerfishes.
Ogcocephalidae is found worldwide in tropical and subtropical seas, but they are not present in the Mediterranean Sea. Species of the genus Coelophrys are benthopelagic with globose bodies and tiny pelvic fins, but all the other known members of Ogcocephalidae have strongly depressed bodies suitable for benthic life only. (Benthopelagic = lives in the water column but is associated with the sea floor. Benthic = living on or near the sea bottom.) In many species, the pelvic and anal fins are stout enough to support the body off the bottom substrate and protected by thick skin, and some species can walk on the bottom using their pectoral and pelvic fins. Due to these adaptations to a life on the bottom of the ocean, Ogcocephalidae fishes are not very skilled swimmers.
Old World Ogcocephalidae batfishes are typically found on the continental slope down to a depth of 2000-3000 meters (6500-10000 feet). One species have been found as far down as 4000 meters (13000 feet). These waters are lightless and we still know very little about them since they are so difficult to explore. New World species can be found inshore to subtidal depths and they are even capable of entering freshwater rivers.
Ogcocephalidae batfishes feed chiefly on fishes and small invertebrates that they find on the bottom.