Cichlids are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, the

Labroidei The Labroidei are a suborder of the Perciformes, the largest order (biology), order of fish. Among others, the suborder includes the wrasses, cichlids, and parrotfish. Timeline of genera ImageSize = width:1000px height:auto barincrement:15px ...

, along with the wrasses ( Labridae), in the order Perciformes, but molecular studies have contradicted this grouping. The closest living relative of cichlids is probably the

convict blenny ''Pholidichthys leucotaenia'', commonly known as the convict blenny/goby or the engineer blenny/goby, is a marine fish from the west-central Pacific Ocean. Despite its common names, it is neither a blenny nor a goby, but is in fact one of two spe ...

, and both families are classified in the 5th edition of ''

Fishes of the World ''Fishes of the World'' by the American ichthyologist Joseph S. Nelson (1937–2011) is a standard reference for fish systematics. Now in its fifth edition (2016), the work is a comprehensive overview of the diversity and classification of the ...

'' as the two families in the Cichliformes, part of the subseries Ovalentaria. This family is both large and diverse. At least 1,650

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

have been scientifically described, making it one of the largest

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

families. New species are discovered annually, and many species remain undescribed. The actual number of species is therefore unknown, with estimates varying between 2,000 and 3,000. Many cichlids, particularly tilapia, are important food fishes, while others, such as the '' Cichla'' species, are valued game fish. The family also includes many popular freshwater aquarium fish kept by hobbyists, including the

angelfish Angelfish may refer to: *Several groups of fish: **Freshwater angelfish, tropical cichlids of the genus ''Pterophyllum'' **Marine angelfish of the family Pomacanthidae **Atlantic pomfret (''Brama brama''), sold by fishmongers as "angelfish" in Sou ...

, oscars, and discus. Cichlids have the largest number of

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...

among

families, most in the

haplochromine __NOTOC__ The haplochromine cichlids are a tribe of cichlids in subfamily Pseudocrenilabrinae called Haplochromini. This group includes the type genus (''Haplochromis'') plus a number of closely related genera such as '' Aulonocara'', '' Astat ...

group. Cichlids are particularly well known for having evolved rapidly into many closely related but morphologically diverse species within large lakes, particularly Lakes Tanganyika, Victoria, Malawi, and

Edward Edward is an English given name. It is derived from the Anglo-Saxon name ''Ēadweard'', composed of the elements '' ēad'' "wealth, fortune; prosperous" and '' weard'' "guardian, protector”. History The name Edward was very popular in Anglo-Sa ...

. Their diversity in the African Great Lakes is important for the study of

speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

in evolution. Many cichlids introduced into waters outside of their natural range have become nuisances. All cichlids practice some form of parental care for their eggs and fry, usually in the form of guarding the eggs and fry or

mouthbrooding Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a va ...

Anatomy and appearance

Cichlids span a wide range of body sizes, from species as small as in length (e.g., female ''

Neolamprologus multifasciatus ''Neolamprologus multifasciatus'' is one of the small shell-dwelling cichlids endemic to Lake Tanganyika. The male reaches in length, and the female only in the aquarium. In the wild, they reach only in standard length of male and female re ...

'') to much larger species approaching in length (''

Boulengerochromis The giant cichlid (''Boulengerochromis microlepis''), also known as the emperor cichlid, is a species of fish in the family Cichlidae, endemic to Lake Tanganyika in Africa.Altolamprologus'', '' Pterophyllum'', and '' Symphysodon'') to species that are cylindrical and highly elongated (such as '' Julidochromis'', '' Teleogramma'', '' Teleocichla'', '' Crenicichla'', and ''

Gobiocichla ''Gobiocichla'' is a small genus of rheophilic cichlids native to the Cross ( Manyu) and Niger Rivers in Africa. Species There are currently two recognized species in this genus: * '' Gobiocichla ethelwynnae'' T. R. Roberts, 1982 * ''Gobiocichl ...

''). Generally, however, cichlids tend to be of medium size, ovate in shape, and slightly laterally compressed, and generally similar to the North American sunfishes in morphology, behavior, and ecology. Cichlids share a single key trait - the fusion of the lower pharyngeal bones into a single tooth-bearing structure. A complex set of muscles allows the upper and lower pharyngeal bones to be used as a second set of jaws for processing food, allowing a division of labor between the "true jaws" ( mandibles) and the " pharyngeal jaws". Cichlids are efficient and often highly specialized feeders that capture and process a very wide variety of food items. This is assumed to be one reason why they are so diverse. The features that distinguish them from the other families in the Labroidei include: *A single nostril on each side of the forehead, instead of two *No bony shelf below the orbit of the eye *Division of the

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...

organ into two sections, one on the upper half of the flank and a second along the midline of the flank from about halfway along the body to the base of the tail (except for genera ''Teleogramma'' and ''Gobiocichla'') *A distinctively shaped otolith *The

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

's left-side exit from the stomach instead of its right side as in other Labroidei

Taxonomy

Kullander (1998) recognizes eight

subfamilies In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

of cichlids: the

Astronotinae The Astronotinae are a subfamily of cichlids from South America, where they are found in the Amazon, Orinoco, Paraná, and Paraguay River basins, and various rivers in the Guianas. The subfamily includes three genera, each with two species. Alth ...

Cichlasomatinae The Cichlasomatinae are a subfamily of cichlid fishes, including all ciclids native to the Greater Antilles (Cuba and Hispaniola), United States (southern Texas), Mexico and Central America, and many of the cichlids from South America (the other ...

Cichlinae The Cichlinae are a subfamily of fishes in the cichlid family, native to South America. This subfamily consists of approximately 117 described species as of July 2017. Some authors have suggested that the Cichlinae encompasses all of the Neotr ...

, Etroplinae,

Geophaginae Geophagini is a tribe of cichlids from the subfamily Cichlinae, the American cichlids. It is the sister taxon to the clade which includes the Cichlasomatini and Heroini. Fishes in the Geophagini are distributed from Panama south to Argentina, ...

, Heterochromidinae, Pseudocrenilabrinae, and Retroculinae. A ninth subfamily, the Ptychochrominae, was later recognized by Sparks and Smith. Cichlid taxonomy is still debated, and classification of

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

cannot yet be definitively given. A comprehensive system of assigning

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

genera is still lacking, and there is not complete agreement on what genera should be recognized in this family. As an example of the classification problems, Kullander placed the African genus '' Heterochromis'' phylogenetically within Neotropical cichlids, although later papers concluded otherwise. Other problems center upon the identity of the putative common ancestor for the Lake Victoria superflock (many closely related species sharing a single habitat), and the ancestral lineages of Lake Tanganyikan cichlids. Aequidens pallidus MH-MCZArtwork ARC 209-201

Aequidens pallidus MH-MCZArtwork ARC 209-201

Comparisons between a morphologically based phylogeny and analyses of gene loci produce differences at the genus level. A consensus remains that the Cichlidae as a family are monophyletic. In cichlid taxonomy,

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolo ...

was formerly used as a classifying characteristic, but this was complicated because in many cichlids, tooth shapes change with age, due to wear, and cannot be relied upon. Genome sequencing and other technologies transformed cichlid taxonomy.

Distribution and habitat

Cichlids are one of the largest vertebrate families in the world. They are most diverse in Africa and South America. Africa alone is host to at least an estimated 1,600 species.

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

and

Mexico Mexico ( Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guate ...

have about 120 species, as far north as the

Rio Grande The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio G ...

South Texas South Texas is a region of the U.S. state of Texas that lies roughly south of—and includes—San Antonio. The southern and western boundary is the Rio Grande, and to the east it is the Gulf of Mexico. The population of this region is about 4.96 ...

. Madagascar has its own distinctive species ('' Katria'', '' Oxylapia'', '' Paratilapia'', '' Paretroplus'', '' Ptychochromis'', and ''

Ptychochromoides ''Ptychochromoides'' is a genus of cichlids endemic to Madagascar. Of the three described species, two are critically endangered and one was considered extinct until rediscovered in late 2010.Toronto Zoo (2010). Mad Fishes 2010 – Fish conserva ...

''), only distantly related to those on the African mainland. Native cichlids are largely absent in Asia, except for 9 species in

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon () or the Lebanese Republic, is a country in Western Asia. It is located between Syria to Lebanon–Syria border, the north and east and Israel to Blue ...

, and

Syria Syria ( ar, سُورِيَا or سُورِيَة, translit=Sūriyā), officially the Syrian Arab Republic ( ar, الجمهورية العربية السورية, al-Jumhūrīyah al-ʻArabīyah as-Sūrīyah), is a Western Asian country loc ...

('' Astatotilapia flaviijosephi'', '' Oreochromis aureus'', '' O. niloticus'', '' Sarotherodon galilaeus'', '' Coptodon zillii'', and ''

Tristramella ''Tristramella'' is a genus of oreochromines, freshwater fishes in the cichlid family. The members of this genus prefer standing waters and their native range is restricted to the Jordan River system, including Lake Tiberias (Kinneret), in Isr ...

'' spp.), two in

Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkm ...

('' Iranocichla''), and three in

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

and

Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...

('' Etroplus'' and '' Pseudetroplus''). If disregarding Trinidad and Tobago (where the few native cichlids are members of genera that are widespread in the South American mainland), the three species from the genus '' Nandopsis'' are the only cichlids from the Antilles in the Caribbean, specifically

Cuba Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...

and

Hispaniola Hispaniola (, also ; es, La Española; Latin and french: Hispaniola; ht, Ispayola; tnq, Ayiti or Quisqueya) is an island in the Caribbean that is part of the Greater Antilles. Hispaniola is the most populous island in the West Indies, and th ...

. Europe, Australia, Antarctica, and North America north of the Rio Grande drainage have no native cichlids, although in

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...

, Japan, northern Australia, and elsewhere, feral populations of cichlids have become established as exotics. Although most cichlids are found at relatively shallow depths, several exceptions do exist. The deepest known occurrences are '' Trematocara'' at more than below the surface in

Lake Tanganyika Lake Tanganyika () is an African Great Lake. It is the second-oldest freshwater lake in the world, the second-largest by volume, and the second-deepest, in all cases after Lake Baikal in Siberia. It is the world's longest freshwater lake. ...

.Loiselle, Paul (1994). The Cichlid Aquarium, p. 304. Tetra Press, Germany. . Others found in relatively deep waters include species such as '' Alticorpus macrocleithrum'' and '' Pallidochromis tokolosh'' down to below the surface in Lake Malawi, and the whitish (non pigmented) and blind ''

Lamprologus lethops ''Lamprologus lethops'' is a species of cichlid fish from areas with fast current in the Congo River in Central Africa, where it is believed to live in depths as great as or below the surface. It reaches up to about in standard length, with ...

'', which is believed to live as deep as below the surface in the Congo River. Cichlids are less commonly found in brackish and saltwater habitats, though many species tolerate brackish water for extended periods; ''

Mayaheros urophthalmus ''Mayaheros urophthalmus'', also known as the Mayan cichlid or Mexican mojarra is a species of cichlid. Taxonomy Previously, this species was a member of the genus ''Cichlasoma'' and the subgeneric section '' Nandopsis''. However, the genus ''C ...

'', for example, is equally at home in freshwater marshes and mangrove swamps, and lives and breeds in saltwater environments such as the mangrove belts around barrier islands. Several species of '' Tilapia'', '' Sarotherodon'', and '' Oreochromis'' are

euryhaline Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly (''Poecilia sphenops'') which can live in fresh water, brackish water, or salt water. The green crab (''Carcinus maenas'') is an e ...

and can disperse along brackish coastlines between rivers. Only a few cichlids, however, inhabit primarily brackish or salt water, most notably '' Etroplus maculatus'', '' Etroplus suratensis'', and ''

Sarotherodon melanotheron The blackchin tilapia (''Sarotherodon melanotheron'') is a species of cichlid native to coastal west Africa. It is a paternal mouthbrooder which has been introduced to Asia and North America. In the Philippines, it is also informally called ''g ...

''. The perhaps most extreme habitats for cichlids are the warm hypersaline lakes where the members of the genera '' Alcolapia'' and '' Danakilia'' are found.

Lake Abaeded A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

Eritrea Eritrea ( ; ti, ኤርትራ, Ertra, ; ar, إرتريا, ʾIritriyā), officially the State of Eritrea, is a country in the Horn of Africa region of Eastern Africa, with its capital and largest city at Asmara. It is bordered by Ethiopia ...

encompasses the entire distribution of '' D. dinicolai'', and its temperature ranges from . With the exception of the species from Cuba, Hispaniola, and Madagascar, cichlids have not reached any oceanic island and have a predominantly Gondwanan distribution, showing the precise sister relationships predicted by

vicariance Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

: Africa-South America and India-Madagascar. The dispersal hypothesis, in contrast, requires cichlids to have negotiated thousands of kilometers of open ocean between India and Madagascar without colonizing any other island, or for that matter, crossing the Mozambique Channel to Africa. Although the vast majority of Malagasy cichlids are entirely restricted to fresh water, '' Ptychochromis grandidieri'' and '' Paretroplus polyactis'' are commonly found in coastal brackish water and are apparently salt tolerant, as is also the case for '' Etroplus maculatus'' and '' E. suratensis'' from India and Sri Lanka.

Ecology

Feeding

Within the cichlid family, carnivores, herbivores, omnivores, planktivores, and detritivores are known, meaning the Cichlidae encompass essentially the full range of food consumption possible in the animal kingdom. Various species have morphological adaptations for specific food sources, but most cichlids consume a wider variety of foods based on availability. Carnivorous cichlids can be further divided into piscivorous and molluscivorous, since the morphology and hunting behavior differ greatly between the two categories. Piscivorous cichlids eat other fish, fry, larvae, and eggs. Some species eat the offspring of mouthbrooders by head-ramming, wherein the hunter shoves its head into the mouth of a female to expel her young and eat them. Molluscivorous cichlids have several hunting strategies amongst the varieties within the group. Lake Malawi cichlids consume substrate and filter it out through their gill rakers to eat the mollusks that were in the substrate. Gill rakers are finger-like structures that line the gills of some fish to catch any food that might escape through their gills. Pseudotropheus Crabo Male

Many cichlids are primarily herbivores, feeding on

algae Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...

(e.g. ''Petrochromis'') and plants (e.g. '' Etroplus suratensis''). Small animals, particularly invertebrates, are only a minor part of their diets. Other cichlids are detritivores and eat organic material, called ''Aufwuchs'' (offal); among these species are the tilapiines of the genera '' Oreochromis'', '' Sarotherodon'', and ''Tilapia (genus), Tilapia''. Other cichlids are carnivore, predatory and eat little or no plant matter. These include generalists that catch a variety of small animals, including other fishes and insect larvae (e.g. '' Pterophyllum''), as well as variety of specialists. ''Trematocranus'' is a specialized snail-eater, while ''Pungu maclareni'' feeds on Porifera, sponges. A number of cichlids feed on other fish, either entirely or in part. '' Crenicichla'' species are stealth predators that lunge from concealment at passing small fish, while ''Rhamphochromis'' species are open-water pursuit predators that chase down their prey. Paedophagy, Paedophagous cichlids such as the ''Caprichromis'' species eat other species' eggs or young, in some cases ramming the heads of mouthbrooding species to force them to disgorge their young. Among the more unusual feeding strategies are those of ''Corematodus'', ''Docimodus, Docimodus evelynae'', ''Plecodus'', ''Perissodus'', and ''Genyochromis'' spp., which feed on scales and fins of other fishes, a behavior known as lepidophagy, along with the death-mimicking behaviour of ''Nimbochromis'' and ''Parachromis'' species, which lay motionless, luring small fish to their side prior to ambush. This variety of feeding styles has helped cichlids to inhabit similarly varied habitats. Its pharyngeal teeth (in the throat) afford cichlids so many "niche" feeding strategies, because the jaws pick and hold food, while the pharyngeal teeth crush the prey.

Behavior

Aggression

Aggressive behavior in cichlids is ritualized and consists of multiple displays used to seek confrontation while being involved in evaluation of competitors, coinciding with temporal proximity to mating. Displays of ritualized aggression in cichlids include a remarkably rapid change in coloration, during which a successfully dominant territorial male assumes a more vivid and brighter coloration, while a subordinate or "nonterritorial" male assumes a dull-pale coloration. In addition to color displays, cichlids employ their

s to sense movements of water around their opponents to evaluate the competing male for physical traits/fitness. Male cichlids are very territorial due to the pressure of reproduction, and establish their territory and social status by physically driving out challenging males (novel intruders) through lateral displays (parallel orientation, uncovering gills), biting, or mouth fights (head-on collisions of open mouths, measuring jaw sizes, and biting each other's jaws). The cichlid social dichotomy is composed of a single dominant with multiple subordinates, where the physical aggression of males becomes a contest for resources (mates, territory, food). Female cichlids prefer to mate with a successfully Alpha (ethology), alpha male with vivid coloration, whose territory has food readily available.

Mating

Cichlids mate either monogamously or polygamously. The mating system of a given cichlid species is not consistently associated with its brooding system. For example, although most monogamous cichlids are not mouthbrooders, ''Chromidotilapia'', ''Gymnogeophagus'', ''Spathodus'', and ''Tanganicodus'' all include – or consist entirely of – monogamous mouthbrooders. In contrast, numerous open- or cave-spawning cichlids are polygamous; examples include many ''Apistogramma'', ''Lamprologus'', ''Nannacara'', and ''Pelvicachromis'' species. Most adult male cichlids, specifically in the cichlid tribe Haplochromini, exhibit a unique pattern of oval-shaped color dots on their anal fins. These phenomena, known as egg spots, aid in the mouthbrooding mechanisms of cichlids. The egg spots consist of carotenoid-based pigment cells, which indicate a high cost to the organism, when considering that fish are not able to synthesize their own carotenoids. The mimicry of egg spots is used by males for the fertilization process. Mouthbrooding females lay eggs and immediately snatch them up with their mouths. Over millions of years, male cichlids have evolved egg spots to initiate the fertilization process more efficiently. When the females are snatching up the eggs into their mouth, the males gyrate their anal fins, which illuminates the egg spots on his tail. Afterwards, the female, believing these are her eggs, places her mouth to the anal fin (specifically the genital papilla) of the male, which is when he discharges sperm into her mouth and fertilizes the eggs. The genuine color of egg spots is a yellow, red, or orange inner circle with a colorless ring surrounding the shape. Through phylogenetic analysis, using the mitochondrial ''ND2'' gene, the true egg spots are thought to have evolved in the common ancestor of the ''Astatoreochromis'' lineage and the modern ''Haplochrominis'' species. This ancestor was most likely riverine in origin, based on the most parsimonious representation of habitat type in the cichlid family. The presence of egg spots in a turbid riverine environment would seem particularly beneficial and necessary for intraspecies communication. Two pigmentation genes are found to be associated with egg-spot patterning and color arrangement. These are ''fhl2-a'' and ''fhl2-b'', which are paralogs. These genes aid in pattern formation and cell-fate determination in early embryonic development. The highest expression of these genes was temporally correlated with egg-spot formation. A short, interspersed, repetitive element was also seen to be associated with egg spots. Specifically, it was evident upstream of the transcriptional start site of ''fhl2'' in only ''Haplochrominis'' species with egg spots

Brood care

Pit spawning in cichlids

Pit spawning, also referred to as substrate breeding, is a behavior in cichlid fish in which a fish builds a pit in the sand or ground, where a pair court and consequently spawn. Many different factors go into this behavior of pit spawning, including female choice of the male and pit size, as well as the male defense of the pits once they are dug in the sand. Cichlids are often divided into two main groups: mouthbrooders and substrate brooders. Different parenting investment levels and behaviors are associated with each type of reproduction. As pit spawning is a reproductive behavior, many different physiological changes occur in the cichlid while this process is occurring that interfere with social interaction. Different kinds of species that pit spawn, and many different morphological changes occur because of this behavioral experience. Pit spawning is an evolved behavior across the cichlid group. Phylogenetic evidence from cichlids in Lake Tanganyika could be helpful in uncovering the evolution of their reproductive behaviors. Several important behaviors are associated with pit spawning, including parental care, food provisioning, and brood guarding.

Mouth brooding vs. pit spawning

One of the differences studied in African cichlids is reproductive behavior. Some species pit spawn and some are known as mouth brooders. Mouthbrooding is a reproductive technique where the fish scoop up eggs and fry for protection. While this behavior differs from species to species in the details, the general basis of the behavior is the same. Mouthbrooding also affects how they choose their mates and breeding grounds. In a 1995 study, Nelson found that in pit-spawning females choose males for mating based on the size of the pit that they dig, as well as some of the physical characteristics seen in the males. Pit spawning also differs from mouth brooding in the size and postnatal care exhibited. Eggs that have been hatched from pit-spawning cichlids are usually smaller than those of mouthbrooders. Pit-spawners' eggs are usually around 2 mm, while mouthbrooders are typically around 7 mm. While different behaviors take place postnatally between mouthbrooders and pit spawners, some similarities exist. Females in both mouthbrooders and pit-spawning cichlids take care of their young after they are hatched. In some cases, both parents exhibit care, but the female always cares for the eggs and newly hatched fry.

Pit spawning process

Many species of cichlids use pit spawning, but one of the less commonly studied species that exhibits this behavior is the Neotropical ''Cichlasoma dimerus''. This fish is a substrate breeder that displays biparental care after the fry have hatched from their eggs. One study examined reproductive and social behaviors of this species to see how they accomplished their pit spawning, including different physiological factors such as hormone levels, color changes, and plasma cortisol levels. The entire spawning process could take about 90 minutes and 400 to 800 eggs could be laid. The female deposits about 10 eggs at a time, attaching them to the spawning surface, which may be a pit constructed on the substrate or another surface. The number of eggs laid was correlated to the space available on the substrate. Once the eggs were attached, the male swam over the eggs and fertilized them. The parents would then dig pits in the sand, 10–20 cm wide and 5–10 cm deep, where larvae were transferred after hatching. Larvae began swimming 8 days after fertilization and parenting behaviors and some of the physiological factors measured changed.

Color changes

In the same study, color changes were present before and after the pit spawning occurred. For example, after the larvae were transferred and the pits were beginning to be protected, their fins turned a dark grey color. In another study, of the rainbow cichlid, ''Herotilapia multispinosa'', e color changes occurred throughout the spawning process. Before spawning, the rainbow cichlid was an olive color with grey bands. Once spawning behaviors started, the body and fins of the fish became a more golden color. When the eggs were finished being laid, the pelvic fin all the way back to the caudal fin turned to a darker color and blackened in both the males and the females.

Pit sizes

Females prefer a bigger pit size when choosing where to lay eggs. Differences are seen in the sizes of pits that created, as well as a change in the morphology of the pits. Evolutionary differences between species of fish may cause them to either create pits or castles when spawning. The differences were changes in the way that each species fed, their macrohabitats, and the abilities of their sensory systems.

Evolution

Cichlids are renowned for their recent, rapid evolutionary radiation, both across the entire clade and within different communities across separate habitats. Within their phylogeny, many parallel instances are seen of lineages evolving to the same trait and multiple cases of reversion to an ancestral trait. The family Cichlidae arose between 80 and 100 million years ago within the order Perciformes (perch-like fishes). Cichlidae can be split into a few groups based on their geographic location: Madagascar, Indian, African, and Neotropical (or South American). The most famous and diverse group, the African cichlids, can be further split either into Eastern and Western varieties, or into groups depending on which lake the species is from: Lake Malawi, Lake Victoria, or

. Of these subgroups, the Madagascar and Indian cichlids are the most basal and least diverse. Of the African cichlids, the West African or Lake Tanganyika cichlids are the most basal. Cichlids' common ancestor is believed to have been a spit-spawning species. Both Madagascar and Indian cichlids retain this feature. However, of the African cichlids, all extant substrate brooding species originate solely from Lake Tanganyika. The ancestor of the Lake Malawi and Lake Victoria cichlids were mouthbrooders. Similarly, only around 30% of South American cichlids are thought to retain the ancestral substrate-brooding trait. Mouthbrooding is thought to have evolved individually up to 14 times, and a return to substrate brooding as many as three separate times between both African and Neotropical species.

Associated behaviors

Cichlids have a great variety of behaviors associated with substrate brooding, including courtship and parental care alongside the brooding and nest-building behaviors needed for pit spawning. Cichlids' behavior typically revolves around establishing and defending territories when not courting, brooding, or raising young. Encounters between males and males or females and females are agonistic, while an encounter between a male and female leads to courtship. Courtship in male cichlids follows the establishment of some form of territory, sometimes coupled with building a bower to attract mates. After this, males may attempt to attract female cichlids to their territories by a variety of lekking display strategies or otherwise seek out females of their species. However, cichlids, at the time of spawning, undergo a behavioral change such that they become less receptive to outside interactions. This is often coupled with some physiological change in appearance.

Brood care

Cichlids can have maternal, paternal, or biparental care. Maternal care is most common among mouthbrooders, but cichlids' common ancestor is thought to exhibit paternal-only care. Other individuals outside of the parents may also play a role in raising young; in the biparental daffodil cichlid (''Neolamprologus pulcher''), closely related satellite males, those males that surround other males' territories and attempt to mate with female cichlids in the area, help rear the primary males' offspring and their own. A common form of brood care involves food provisioning. For example, females of lyretail cichlids (''Neolamprologus modabu'') dig at sandy substrate more to push nutritional detritus and zooplankton into the surrounding water. Adult of '' N. modabu'' perform this strategy to collect food for themselves, but dig more when offspring are present, likely to feed their fry. This substrate-disruption strategy is rather common and can also be seen in convict cichlids (''Cichlasoma nigrofasciatum''). Other cichlids have an ectothermal mucus that they grow and feed to their young, while still others chew and distribute caught food to offspring. These strategies, however, are less common in pit-spawning cichlids. Managuense with eggs

Cichlids have highly organized breeding activities. All species show some form of parental care for both Egg (biology), eggs and larvae, often nurturing free-swimming young until they are weeks or months old. Communal parental care, where multiple monogamous pairs care for a mixed school of young have also been observed in multiple cichlid species, including ''Amphilophus citrinellus'', '' Etroplus suratensis'', and ''Tilapia rendalli''. Comparably, the fry of ''Neolamprologus brichardi'', a species that commonly lives in large groups, are protected not only by the adults, but also by older Juvenile (organism), juveniles from previous spawns. Several cichlids, including discus ('' Symphysodon'' spp.), some ''Amphilophus'' species, '' Etroplus'', and ''Uaru'' species, feed their young with a skin secretion from mucous glands. The species ''Neolamprologus pulcher'' uses a cooperative breeding system, in which one breeding pair has many helpers that are subordinate to the dominant breeders. Parental care falls into one of four categories: substrate or open brooders, secretive cave brooders (also known as guarding speleophils), and at least two types of mouthbrooders, ovophile mouthbrooders and larvophile mouthbrooders.

Open brooding

Open- or substrate-brooding cichlids lay their eggs in the open, on rocks, leaves, or logs. Examples of open-brooding cichlids include '' Pterophyllum'' and ''Symphysodon'' species and ''Anomalochromis thomasi''. Male and female parents usually engage in differing brooding roles. Most commonly, the male patrols the pair's territory and repels intruders, while the female fans water over the eggs, removing the infertile ones, and leading the fry while foraging. Both sexes are able to perform the full range of parenting behaviours.

Cave brooding

Secretive cave-spawning cichlids lay their eggs in caves, crevices, holes, or Shell dweller, discarded mollusc shells, frequently attaching the eggs to the roof of the chamber. Examples include ''Pelvicachromis pulcher, Pelvicachromis'' spp., ''Convict cichlid, Archocentrus'' spp., and ''Apistogramma'' spp. Free-swimming fry and parents communicate in captivity and in the wild. Frequently, this communication is based on body movements, such as shaking and pelvic fin flicking. In addition, open- and cave-brooding parents assist in finding food resources for their fry. Multiple neotropical cichlid species perform leaf-turning and fin-digging behaviors.

Ovophile mouthbrooding

Ovophile mouthbrooders incubate their eggs in their mouths as soon as they are laid, and frequently mouthbrood free-swimming fry for several weeks. Examples include many East African Rift lakes (Lake Malawi National Park, Lake Malawi,

, and Lake Victoria) endemics, e.g.: ''Maylandia'', ''Pseudotropheus'', ''Tropheus'', and ''Astatotilapia burtoni'', along with some South American cichlids such as ''Geophagus steindachneri''.

Larvophile mouthbrooding

Larvophile mouthbrooders lay eggs in the open or in a cave and take the hatched larvae into the mouth. Examples include some variants of ''Geophagus altifrons'', and some ''Aequidens'', ''Gymnogeophagus'', and ''Satanoperca'', as well as ''Oreochromis mossambicus'' and ''Oreochromis niloticus''. Mouthbrooders, whether of eggs or larvae, are predominantly females. Exceptions that also involve the males include eretmodine cichlids (genera ''Spathodus'', ''Eretmodus'', and ''Tanganicodus''), some '' Sarotherodon'' species (such as ''

''), ''Chromidotilapia guentheri'', and some ''Aequidens'' species. This method appears to have evolved independently in several groups of African cichlids.

Speciation

Cichlids provide scientists with a unique perspective of speciation, having become extremely diverse in the more recent geological past. Some of the contributing factors to their diversification are believed to be the various forms of prey processing displayed by cichlid pharyngeal jaw apparatus. These different jaw apparatus allow for a broad range of feeding strategies, including algae scraping, snail crushing, planktivory, piscivory, and insectivory. Some cichlids can also show phenotypic plasticity in their pharyngeal jaws, which can also help lead to speciation. In response to different diets or food scarcity, members of the same species can display different jaw morphologies that are better suited to different feeding strategies. As species members begin to concentrate around different food sources and continue their lifecycle, they most likely spawn with like individuals. This can reinforce the jaw morphology and given enough time, create new species. Such a process can happen through allopatric speciation, whereby species diverge according to different selection pressures in different geographical areas, or through sympatric speciation, by which new species evolve from a common ancestor while remaining in the same area. In Apoyo Lagoon Natural Reserve, Lake Apoyo in Nicaragua, ''Amphilophus zaliosus'' and its sister species ''Amphilophus citrinellus'' display many of the criteria needed for sympatric speciation. In the Rift Valley lakes, African rift lake system, cichlid species in numerous distinct lakes evolved from a shared hybrid swarm.

Population status

In 2010, the International Union for Conservation of Nature classified 184 species as Vulnerable species, vulnerable, 52 as Endangered species, endangered, and 106 as critically endangered.IUCN 2010.
IUCN Red List of Threatened Species.
' Version 2010.4. Retrieved 26 April 2011. At present, the IUCN only lists Yssichromis sp. nov. "argens", ''Yssichromis'' sp. nov. ''argens'' as extinct in the wild, and six species are listed as entirely extinct, but many more possibly belong in these categories (for example, ''Haplochromis aelocephalus'', ''Haplochromis apogonoides, H. apogonoides'', ''Haplochromis dentex, H. dentex'', ''Haplochromis dichrourus, H. dichrourus'', and numerous other members of the genus ''Haplochromis'' have not been seen since the 1980s, but are maintained as critically endangered on the small chance that tiny –but currently unknown– populations survive).

Lake Victoria

Because of the introduced Nile perch (''Lates niloticus''), Nile tilapia (''Oreochromis niloticus''), and water hyacinth, deforestation that led to water siltation, and overfishing, many Lake Victoria cichlid species have become extinct or been drastically reduced. By around 1980, lake fisheries yielded only 1% cichlids, a drastic decline from 80% in earlier years. By far the largest Lake Victoria group is the haplochromine cichlids, with more than 500 species, but at least 200 of these (about 40%) have become extinct, and many others are seriously threatened.Fiedler, P.L.; and P.M. Kareiva, editors (1998). Conservation Biology: For the Coming Decade. 2nd edition. pp. 209—210. Initially it was feared that the percentage of extinct species was even higher, but some species have been rediscovered after the Nile perch started to decline in the 1990s.IUCN Red Lists
Geographic Patterns
Eastern Africa. Retrieved 25 March 2017. Some species have survived in nearby small satellite lakes, or in refugia among rocks or papyrus sedges (protecting them from the Nile perch), or have adapted to the human-induced changes in the lake itself. The species were often specialists and these were not affected to the same extent. For example, the piscivorous haplochromines were particularly hard hit with a high number of extinctions, while the Planktivore, zooplanktivorous haplochromines reached densities in 2001 that were similar to before the drastic decline, although consisting of fewer species and with some changes in their ecology.

Food and game fish

Although cichlids are mostly small- to medium-sized, many are notable as food and game fishes. With few thick rib bones and tasty flesh, artisan fishing is not uncommon in Central America and South America, as well as areas surrounding the African Rift Valley lakes, rift lakes.

Tilapia

The most important food cichlids, however, are the tilapiines of North Africa. Fast growing, tolerant of stocking density, and adaptable, tilapiine species have been introduced and farmed extensively in many parts of Asia and are increasingly common aquaculture targets elsewhere. Farmed tilapia production is about annually, with an estimated value of US$1.8 billion, about equal to that of salmon and trout. Unlike those carnivorous fish, tilapia can feed on

or any plant-based food. This reduces the cost of tilapia farming, reduces fishing pressure on prey species, avoids concentrating toxins that accumulate at higher levels of the food chain, and makes tilapia the preferred "aquatic chickens" of the trade.

Game fish

Many large cichlids are popular game fish. The peacock bass ('' Cichla'' species) of South America is one of the most popular sport fishing, sportfish. It was introduced in many waters around the world. In

, this fish generates millions of hours of fishing and sportfishing revenue of more than US$8 million a year. Other cichlids preferred by anglers include the oscar (fish), oscar, Mayan cichlid (''Cichlasoma urophthalmus''), and jaguar guapote (''Parachromis managuensis'').

Aquarium fish

Since 1945, cichlids have become increasingly popular as aquarium fish.Sands D (1994) ''A fishkeepers guide to Central American cichlids.'' Tetra Press. Belgium pg 59-60.Leibel WS (1993) ''A fishkeepers guide to South American cichlids.'' Tetra Press. Belgium pg 12–14. The most common species in hobbyist aquaria is ''Pterophyllum scalare'' from the Amazon River basin in tropical South America, known in the trade as the "

". Other popular or readily available species include the Oscar (fish), oscar (''Astronotus ocellatus''), convict cichlid (''Archocentrus nigrofasciatus'') and Symphysodon, discus fish (''Symphysodon'').

Hybrids and selective breeding

Some cichlids readily Hybrid (biology), hybridize with related species, both in the wild and under artificial conditions. Other groups of fishes, such as European Cyprinidae, cyprinids, also hybridize. Unusually, cichlid hybrids have been put to extensive commercial use, in particular for aquaculture and aquaria. The hybrid red strain of tilapia, for example, is often preferred in aquaculture for its rapid growth. Tilapia hybridization can produce all-male populations to control stock density or prevent reproduction in ponds.

Aquarium hybrids

The most common aquarium hybrid is perhaps the blood parrot cichlid, which is a cross of several species, especially from species in the genus ''Amphilophus''. (There are many hypotheses, but the most likely is: ''Amphilophus labiatus'' x ''Vieja melanurus, Vieja synspillus'' With a triangular-shaped mouth, an abnormal Vertebral column, spine, and an occasionally missing caudal fin (known as the "love heart" parrot cichlid), the fish is controversial among aquarists. Some have called blood parrot cichlids "the Frankenstein monster of the fish world". Another notable hybrid, the flowerhorn cichlid, was very popular in some parts of Asia from 2001 until late 2003, and is believed to bring good luck to its owner. The popularity of the flowerhorn cichlid declined in 2004. Owners released many specimens into the rivers and canals of Malaysia and Singapore, where they threaten endemic communities. Long finned oscar

Numerous cichlid species have been selective breeding, selectively bred to develop ornamental aquarium strains. The most intensive programs have involved angelfish and discus, and many mutations that affect both coloration and fins are known. Other cichlids have been bred for albino, Leucism, leucistic, and Xanthochromism, xanthistic pigment mutations, including Oscar (fish), oscars, convict cichlid and ''Pelvicachromis pulcher''. Both dominance (genetics), dominant and dominance (genetics), recessive pigment mutations have been observed. Kornfield I (1991) Genetics. In: ''Cichlid Fishes: behaviour, ecology and evolution'' Ed. Keenleyside MHA. Chapman and Hall, London. p. 109-115. In convict cichlids, for example, a leucistic coloration is recessively inherited, while in ''Oreochromis niloticus niloticus'', red coloration is caused by a dominant inherited mutation. This selective breeding may have unintended consequences. For example, hybrid strains of ''Ram cichlid, Mikrogeophagus ramirezi'' have health and fertility problems. Linke H, Staeck L (1994) ''American cichlids I: Dwarf Cichlids. A handbook for their identification, care and breeding.'' Tetra Press. Germany. Similarly, intentional inbreeding can cause physical abnormalities, such as the notched phenotype in Pterophyllum, angelfish.

Genera

The genus list is as per FishBase. Studies are continuing, however, on the members of this family, particularly the haplochromine cichlids of the African rift lakes.

Images of cichlids

File:Astronotus ocellatus.jpg, The Oscar (fish), oscar (''Astronotus ocellatus'') is one of the most popular cichlids in the fishkeeping hobby. File:ButterflyPeacockBass 01.jpg, The butterfly peacock bass (''Cichla ocellaris'') was introduced intentionally in

as sport fishing, gamefish. File:Oreochromis niloticus.jpg, The Nile tilapia (''Oreochromis niloticus'') is farmed extensively as food fish in many parts of the world. File:Pterophyllum scalare-narybek.jpg, The angelfish (''Pterophyllum scalare'') has long been commercially bred for the aquarium trade. File:Maylandia lombardoi.jpg, Sexual dimorphism is common in cichlids. Shown here are a male (front, with egg spots) and a female (rear) ''Maylandia lombardoi''. File:Mikrogeophagus.jpg, A pair of blue rams (''Mikrogeophagus ramirezi''), male in front, female behind. Many cichlids form strong pair bonds while breeding. File:Diskuslaich1a.jpeg, A discus (''Symphysodon, Symphysodon spp.'') is guarding its eggs. Advanced broodcare is one of the defining characteristics of cichlids. File:Adult_male_livingstonii.png, Lake Malawi, Eastern Africa, is home to numerous cichild species including this Livingston's cichlid (''Nimbochromis livingstonii''). File:Maylandia lombardoi male Lake Malawi Cichlid yellow.jpg, Also from Lake Malawi File:Labeotropheus sp Lake Malawi Cichlid pale femelle.jpg, Also from Lake Malawi File:Lamprologusstappersimalemcl.jpg, A Shell dweller, shell-brooding cichlid of the genus ''Lamprologus'' from

in East Africa File:Herichthys cyanoguttatum (Rio Grande Cichlid).jpg, The Texas cichlid (''Herichthys cyanoguttatus'') is the only cichlid native to the United States. File:Pelvicachromis pulcher (female).jpg, ''Pelvicachromis pulcher'' is a West African riverine cichlid, and part of the aquarists dwarf cichlid group. File:Flowerhorn.jpg, The flowerhorn cichlid is a man-made Hybrid (biology), hybrid that has recently gained popularity among aquarists, particularly in Asia. File:Ivanacara adoketa5164.jpg, ''Ivanacara adoketa'', a dwarf cichlid from Brazil File:Red Terror Festae Chiclid.jpg, The Cichlasoma, red terror cichlid is a highly aggressive species from the rivers of Northeast South America. File:Female Juvenile .jpg, A juvenile female Maylandia lombardoi with faint stripes File:Juvenile Royal Acara.jpg, A juvenile ''Aequidens diadema''

References

External links

*
The Cichlid Fishes of Lake Malawi
by Dr. Michael Oliver.
Vision in Cichlids: Ecomorphology of vision in haplochromine cichlids of Lake Victoria
by Dr. H.J. van der Meer. * {{Authority control Cichlidae, * Cichliformes Fishkeeping Taxa named by Charles Lucien Bonaparte

Anatomy and appearance

Taxonomy

Distribution and habitat

Ecology

Feeding

Behavior

Aggression

Mating

Brood care

Pit spawning in cichlids

Mouth brooding vs. pit spawning

Pit spawning process

Color changes

Pit sizes

Evolution

Associated behaviors

Brood care

Open brooding

Cave brooding

Ovophile mouthbrooding

Larvophile mouthbrooding

Speciation

Population status

Lake Victoria

Food and game fish

Tilapia

Game fish

Aquarium fish

Hybrids and selective breeding

Aquarium hybrids

Genera

Images of cichlids

References

Further reading

External links