Lepidophagy
Lepidophagy is a specialised feeding behaviour in fish that involves eating the scales of other fish. Lepidophagy is widespread, having evolved independently in at least five freshwater families and seven marine families. A related feeding behavior among fish is pterygophagy: feeding on the fins of other fish.
Species
Lepidophagy, or scale-eating, has been reported in a range of fish, including Chanda nama, Plagiotremus, Terapon jarbua, a few Ariopsis and Neoarius species, Pachypterus khavalchor, Macrorhamphoides uradoi, several pencil catfish, some piranha, Exodon paradoxus, Probolodus, Roeboides and Roeboexodon species, Cyprinodon desquamator, along with all six Perissodus species, Xenochromis, Haplochromis welcommei, Docimodus, Corematodus and Genyochromis mento.Several of these scale-eaters also feed on fins of other fish, and many omnivorous or predatory fish may on occasion nip the fins of other fish. Only a few species are specialized fin-eaters, or pterygophagous; these include Belonophago, Eugnathichthys and Phago, Aspidontus, and Smilosicyopus. A somewhat related behavior is found in Magosternarchus, which feed on the tails of other gymnotiform knifefish.
Physiology
Many species of cichlid fish have evolved specialized teeth and mouth structures that make them better able to feed on the scales of other fish. Other species of fish also have a morphology that is better adapted to scale-eating. Many such species' oral structures closely resemble each other even though they live in different habitats, and many also have specialized jaw structures. One species of fish in particular, called Roeboides prognathous, has a jaw structure that is extremely specialized for lepidophagy. Certain species of lepidophagous catfish, Pachypterus khavalchor, have digestive enzymes which help them to more readily break down the fins, eyes, scales of other fish. There are other morphological structures that are important in scale-eating habitats. There are six lepidophagous cichlid species who employ mimicry strategies to deceive their prey: the colors of the cichlid fish closely resemble the colors of some of their prey. However, they not only eat the scales of the fish they resemble, but also prey on a wide range of other species.Behaviour
There are many different behaviours associated within lepidophagous fish. Aggression and attack behaviours like chasing and striking prey are common among Pachypterus khavalchor catfish, who then eat the fallen scales of their prey. The attack behaviour of the wimple piranha Catoprion mento, whose diet consists mainly of scales, is described as a "high-speed" attack. They ram into their prey with their mouth open, biting the prey to obtain their scales. Perissodus microlepis cichlid fish tear off the scales of their prey as they swim past. This is very different from other lepidophagous species, who merely knock the scales loose by striking the prey.There are differences and similarities in lepidophagous behaviours across species. For example, the siluroid catfish's attacking behaviour is similar to that of the Probolodus heterostomus: they both follow their prey and attack their prey from behind. This is different from the behaviour of Roeboides prognatus and Exodon paradoxus, who remove scales more easily by attacking a specific part of their prey's body called the caudal area. Many studies have examined the hunting behaviours of scale-eating fish and how those behaviours have evolved over time. Certain species of cichlid aggressively mimic the behaviours of their prey, a tactic rarely used by other scale-eating fish species.