Lepidophagy is a specialisedfeeding behaviour infish that involves eating thescales of other fish.[1] Lepidophagy is widespread, havingevolved independently in at least five freshwater families and seven marine families.[2] A related feeding behavior among fish ispterygophagy: feeding on thefins of other fish.[3]
Lepidophagy, or scale-eating, has been reported in a range of fish, including:Chanda nama (familyAmbassidae),[4]Plagiotremus (familyBlenniidae),[5]Terapon jarbua (familyTerapontidae),[1] a fewAriopsis andNeoarius species (familyAriidae),[6]Pachypterus khavalchor (familyPachypteridae),Macrorhamphoides uradoi (familyTriacanthodidae), severalpencil catfish (familyTrichomycteridae),[5] somepiranha,Exodon paradoxus,Probolodus,Roeboides andRoeboexodon species (orderCharaciformes),[2][7][8][9]Cyprinodon desquamator (familyCyprinodontidae), along with bothPerissodus species, all fourPlecodus species,Xenochromis,Haplochromis welcommei,Docimodus,Corematodus andGenyochromis mento (familyCichlidae from theAfrican Great Lakes).[10][11][12]
Several of these scale-eaters also feed on fins of other fish, and manyomnivorous orpredatory fish may on occasion nip the fins of other fish. Only a few species are specialized fin-eaters, or pterygophagous; these includeBelonophago,Eugnathichthys andPhago (familyDistichodontidae),Aspidontus (familyBlenniidae), andSmilosicyopus (familyGobiidae).[3][13] A somewhat related behavior is found inMagosternarchus, which feed on the tails (both fin and connective tissue) of othergymnotiform knifefish.[14]
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.[15] 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.[16] One species of fish in particular, calledRoeboides prognathous, has a jaw structure that is extremely specialized for lepidophagy.[16] 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.[16] 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.[15]
There are many different behaviours associated within lepidophagous fish. Aggression and attack behaviours like chasing and striking prey are common amongPachypterus khavalchor catfish, who then eat the fallen scales of their prey.[16] The attack behaviour of the wimple piranhaCatoprion 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.[17]Perissodus microlepis cichlid fish tear off the scales of their prey as they swim past.[18]This is very different from other lepidophagous species, who merely knock the scales loose by striking the prey.[17]
There are differences and similarities in lepidophagous behaviours across species. For example, the siluroid catfish’s attacking behaviour is similar to that of theProbolodus heterostomus: they both follow their prey and attack their prey from behind. This is different from the behaviour ofRoeboides prognatus andExodon paradoxus, who remove scales more easily by attacking a specific part of their prey’s body called the caudal area.[16] 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,[15] a tactic rarely used by other scale-eating fish species.[15]
The differences in the niche of certain species may play a role in their behaviours. Lepidophagous behaviours only exist in some species.[19]Adaptive radiation has been mentioned in many articles as having a role in the evolution of lepidophagy.[19] There is some evidence to support this but much is also unclear. Some behaviours in certain species of fish support the theory that extreme environments could be potential causes of scale eating behaviours. Some of those species are named below.
In the case ofCyprinodon pupfish, almost all have a diet of algae anddetritus but the speciesCyprinodon desquamator (only scientifically described in 2013; previously known asCyprinodon sp. "lepidophage" orCyprinodon sp. "scale-eater") is different. There are only two known cases where severalCyprinodon species live together: lakes inSan Salvador Island, the Bahamas, and Lake Chichancanab, Mexico. In both cases, the co-occurringCyprinodon species have diverged into feeding on different things and in lakes on San Salvador Island, this includes the scale-eatingC. desquamator (there are no scale-eaters in Lake Chichancanab, althoughC. maya has become a fish-eater).[20]
There is a diverse range of cichilds in Lake Tanganyika in East Africa but the Tanganyikan cichlid tribes,Perissodini andPlecodus, feed on the scales of cichlids and other fishes.[21] The species of cichilds that exhibit scale eating behaviours live in deep water with very low levels of oxygen and have had to rapidly evolve to keep up with a changing environment and lack of food.[19]
Fish scales are a nutritional food source, containing layers ofkeratin andenamel, as well as a dermal portion and a layer of protein-rich mucus. They are a rich source ofcalcium phosphate.[2] However, the energy expended to make a strike versus the amount of scales consumed per strike puts a limit on the size of the lepidophage; such fish seldom exceed 20 cm (8 in) and most are under 12 cm (5 in).[2] Because of this lepidophagous fish usually are much smaller than their prey. Though scales are nutritious, the average amount of scales dislodged and eaten may not be sufficient to make up for the energy lost during the attack.[17] The attack behaviours and strikes that are employed to remove and eat scales have an energy cost and risk of harm to the predator.[22] In light of this, there are also a number of advantages to consuming scales: scales are common, covering the body of most fish species, can be regrown relatively quickly by "prey" fish, are abundant and seasonally reliable, and their removal requires specific behaviours or morphological structures.[2] Scale eating behaviour usually evolves because of lack of food and extreme environmental conditions. The eating of scales and the skin surrounding the scales provides protein-rich nutrients that may not be available elsewhere in the niche.[20]
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