Lepidophagy is a specialised
feeding behaviour in
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...
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'' (
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Ambassidae
The Asiatic glassfishes are a family, the Ambassidae, of freshwater and marine fishes that were formerly classified in the order Perciformes, but most authorities consider this order to be paraphyletic and that the Ambassidae are of uncertain a ...
), ''
Plagiotremus'' (family
Blenniidae),
''
Terapon jarbua'' (family
Terapontidae),
a few ''
Ariopsis'' and ''
Neoarius'' species (family
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones. The family includes about 143 species.
Taxonom ...
), Pachypterus khavalchor (family Pachypteridae), Macrorhamphoides uradoi (family Triacanthodidae), several
pencil catfish (family
Trichomycteridae),
[ some ]piranha
A piranha or piraña (, , or ; or , ) is one of a number of freshwater fish in the family Serrasalmidae, or the subfamily Serrasalminae within the tetra family, Characidae in order Characiformes. These fish inhabit South American rivers, ...
, ''Exodon paradoxus
The bucktooth tetra (''Exodon paradoxus'') is the only member of the genus ''Exodon'' and is a freshwater fish of the characin family (family Characidae) of order Characiformes. It is native to the Amazon Basin and Guyana. Though first describe ...
'', '' Probolodus'', '' Roeboides'' and '' Roeboexodon'' species (order Characiformes), '' Cyprinodon desquamator'' (family Cyprinodontidae), along with both '' Perissodus'' species, all four '' Plecodus'' species, '' Xenochromis'', '' Haplochromis welcommei'', '' Docimodus'', ''Corematodus
''Corematodus'' is a small genus of haplochromine cichlids native to the Lake Malawi basin in Africa. They feed on scales and fins of other cichlids. Konings, Ad (1990). ''Ad Konings' Book of Cichlids and all the other Fishes of Lake Malawi.'' ...
'' and ''Genyochromis mento
''Genyochromis mento'' is a species of haplochromine cichlid endemic to Lake Malawi in East Africa. It is also found in the aquarium
An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one trans ...
'' (family Cichlidae from the African Great Lakes
The African Great Lakes ( sw, Maziwa Makuu; rw, Ibiyaga bigari) are a series of lakes constituting the part of the Rift Valley lakes in and around the East African Rift. They include Lake Victoria, the second-largest fresh water lake in the ...
).
Several of these scale-eaters also feed on fins of other fish, and many omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
or predatory
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
fish may on occasion nip the fins of other fish. Only a few species are specialized fin-eaters, or pterygophagous; these include ''Belonophago
''Belonophago'' is a small genus of distichodontid freshwater fish found in Middle Africa. They are specialized fin-eaters.Lavoué, S.; M.E.Arnegard; D.L. Rabosky; P.B. McIntyre; D. Arcila; R.P. Vari; M. Nishida (2017). Trophic evolution in Afr ...
'', ''Eugnathichthys
''Eugnathichthys'' is a genus of distichodontid fishes found in the Congo basin in Africa. They are specialized predators that feed on the fins of other fish.
Species
The currently recognized species in this genus are:
* '' Eugnathichthys eet ...
'' and '' Phago'' (family Distichodontidae), ''Aspidontus
''Aspidontus'' is a genus of combtooth blennies found in the Pacific and Indian oceans.
Species
There are currently three recognized species in this genus:
* ''Aspidontus dussumieri'' (Valenciennes, 1836) (Lance blenny)
* ''Aspidontus taeniatus ...
'' (family Blenniidae), and '' Smilosicyopus'' (family Gobiidae
Gobiidae or gobies is a family of bony fish in the order Gobiiformes, one of the largest fish families comprising more than 2,000 species in more than 200 genera. Most of gobiid fish are relatively small, typically less than in length, and t ...
).[ A somewhat related behavior is found in '']Magosternarchus
''Magosternarchus'' is a genus of weakly electric knifefish in the family Apteronotidae, containing two species. They are endemic to Brazil, occurring in large river channels in the Amazon River basin. Both species are unusual benthic predator ...
'', which feed on the tails (both fin and connective tissue) 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
The wimple piranha, ''Catoprion mento'', is a specialized, South American species of piranha that feeds on fish scales. There is debates over whether or not this species is considered a true piranha. If it was considered a true piranha, then i ...
'', 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
The bucktooth tetra (''Exodon paradoxus'') is the only member of the genus ''Exodon'' and is a freshwater fish of the characin family (family Characidae) of order Characiformes. It is native to the Amazon Basin and Guyana. Though first describe ...
'', who remove scales more easily by attacking a specific pop art 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.
Niche
The differences in the niche of certain species may play a role in their behaviours. Lepidophagous behaviours only exist in some species. Adaptive radiation has been mentioned in many articles as having a role in the evolution of lepidophagy. 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.
Cyprinodon pupfish
In the case of '' Cyprinodon'' pupfish, almost all have a diet of algae and detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commu ...
but the species '' Cyprinodon desquamator'' (only scientifically described in 2013; previously known as ''Cyprinodon'' sp. "lepidophage" or ''Cyprinodon'' sp. "scale-eater") is different. There are only two known cases where several ''Cyprinodon'' species live together: lakes in San Salvador Island, the Bahamas, and Lake Chichancanab, Mexico. In both cases, the co-occurring ''Cyprinodon'' species have diverged into feeding on different things and in lakes on San Salvador Island, this includes the scale-eating ''C. desquamator'' (there are no scale-eaters in Lake Chichancanab, although '' C. maya'' has become a fish-eater).
Cichlids
There is a diverse range of cichilds in Lake Tanganyika in East Africa but the Tanganyikan cichlid tribes, ''Perissodini'' and ''Plecodus'', feed on the scales of cichlids and other fishes. 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.
Trade-offs
Fish scales are a nutritional food source, containing layers of keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ...
and enamel, as well as a dermal portion and a layer of protein-rich mucus. They are a rich source of calcium phosphate
The term calcium phosphate refers to a family of materials and minerals containing calcium ions (Ca2+) together with inorganic phosphate anions. Some so-called calcium phosphates contain oxide and hydroxide as well. Calcium phosphates are wh ...
. 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 and most are under . 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. The attack behaviours and strikes that are employed to remove and eat scales have an energy cost and risk of harm to the predator. 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. 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.
References
Bibliography
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{{diversity of fish
Ambassidae
Characidae
Ariidae
Cichlidae
Ichthyology
Carnivory