Cichlid - WikiHQ

Cichlids () are a large, diverse, and widespread family of percomorph fish in the family Cichlidae, order Cichliformes. At least 1,760 species have been scientifically described, making it one of the largest vertebrate families, with only the Cyprinidae being more speciose. 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. They are native to the Neotropics, Africa (including Madagascar), the Middle East, and the Indian subcontinent, although some species have been introduced worldwide.

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, oscars, and discus. Cichlids have the largest number of endangered species among vertebrate families, most in the haplochromine group. Cichlids are well known for their rapid evolution into morphologically diverse species flocks within the African Great Lakes. Some of these key morphological differences include jaw and teeth structure, fin, head, and body shape, and most importantly, their coloration. Their diversity in the African Great Lakes is important for the study of speciation 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.

History

One of the reasons of rapid speciation in the African Great Lakes, Victoria, Malawi, and Tanganyika, is their geological and climate history. Tectonic rifting that occurred ~20–25 million years ago created the rift system, eventually forming the basins of the three lakes. Lake Tanganyika, the oldest, formed ~12–9 million years ago, while Lake Malawi deepened more recently during the Pliocene (~5–2 Ma). Sediment core analysis from 1.3 million years ago shows lake-level fluctuations, with at least 24 drops of 200m and 14 drops of 400m in Lake Malawi; these patterns are also seen in the other two lakes.

These patterns of lowstands reduced available habitats and geographically isolated fish populations; highstands refilled the lake, increased habitat availability, and reconnected populations, allowing hybridization and gene flow within the different fish populations.

Anatomy and appearance

Cichlids span a wide range of body sizes, from species as small as in length (e.g., female Neolamprologus multifasciatus) to much larger species approaching in length (Boulengerochromis and Cichla). As a group, cichlids exhibit a similar diversity of body shapes, ranging from strongly laterally compressed species (such as Altolamprologus, Pterophyllum, and Symphysodon) to species that are cylindrical and highly elongated (such as Julidochromis, Teleogramma, Teleocichla, Crenicichla, and Gobiocichla). 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.

Family Cichlidae Bonaparte, 1835
Subfamily Etroplinae Kullander, 1998 (Indian and Madagascan cichlids)
Subfamily Ptychochrominae Sparks, 2004 (Malagasy cichlids)
Subfamily Pseudocrenilabrinae Fowler, 1934 (African cichlids)
Subfamily Cichlinae Bonaparte, 1835 (American cichlids)

In the past, cichlid taxonomy has varied depending on the author. Kullander (1998) recognized eight subfamilies of cichlids: the Astronotinae, Cichlasomatinae, Cichlinae, Etroplinae, Geophaginae, 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 cannot yet be definitively given. A comprehensive system of assigning species to monophyletic 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.

alt=A 19th century watercolor painting of a pale flag cichlid.|thumb|A 19th-century watercolor painting of a pale flag cichlid by [[Jacques Burkhardt|left]]

Phylogeny derived from morphological characters shows differences at the genus level with phylogeny based on genetic loci. A consensus remains that the Cichlidae as a family are monophyletic.

In cichlid taxonomy, dentition 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.

Alternatively, all cichlid species native to the New World, can be classified under the subfamily Cichlinae, while Etroplinae can classify all cichlid species native to the Old World.

External taxonomy

The taxonomic placement of cichlids has long been disputed and variable, and has only recently been largely resolved. In the past, based on morphological characteristics, cichlids were classed in a suborder, the Labroidei, along with the wrasses (Labridae), in the order Perciformes. However, studies incorporating molecular phylogenetics have contradicted this grouping.

More recent phylogenetic studies support the creation of a distinct order, the Cichliformes, to contain the cichlids and their close relatives, which are no longer thought to be closely related to wrasses. The closest living relative of cichlids has been found to be the marine convict blenny, and both families are classified in the 5th edition of Fishes of the World as the two families in the Cichliformes, part of the subseries Ovalentaria. The Catalog of Fishes adopts the same placement, although the leaffishes (which have a similar African and South American distribution) are now also placed in the Cichliformes. Although these interrelationships are now generally well-supported, other authors have interpreted these relationships in differing ways, such as instead placing the cichlids, leaffish, and convict blenny as the most basal members of an expanded Blenniiformes.

Evolution

Modern cichlids have a disjunct distribution consisting of Africa (including Madagascar), the Neotropics (including Cuba and Hispaniola), the Levant, southern Iran, and the southern Indian subcontinent. This distribution has become the subject of much scientific dispute, with it being debated whether modern cichlid distribution is a consequence of the breakup of Gondwana (which would make cichlids a particularly ancient group dating to the Early Cretaceous), or if it is instead based on more recent oceanic dispersal by the cichlids (despite modern members of the group being largely restricted to freshwater).

Proponents of the Gondwanan theory, which saw more support in the past, have noted that the cichlids display the precise sister relationships predicted by Gondwanan distribution: Africa-South America and India-Madagascar, and that with the exception of the species from Cuba, Hispaniola and Madagascar, cichlids have not reached any oceanic island. 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. It is known that during the Paleogene, the Atlantic Ocean between South America and Africa was significantly narrower, and it has been suggested that either now-submerged islands or a large plume from the Congo River may have allowed for a shallower or less saline environment that was conducive for cichlids to disperse from Africa to South America. Under the dispersal hypothesis, it is generally accepted that Africa was the ancestral home for cichlids, from which they dispersed to attain their present distribution. as well as the Middle Eocene (46 mya)–aged Mahenge Formation of Tanzania, suggesting that the divergence between Old and New World cichlids must have occurred prior to this point.

Several African fossil sites that contain cichlids (including the Eocene-aged Mahenge Formation of Tanzania and the Miocene-aged Ngorora Formation of Kenya) appear to represent former maars or rift lakes, and the fossil cichlids present in them appear to represent species flocks akin to those in the modern African rift lakes. This suggests that rapid diversification within enclosed ecosystems is a longstanding trait of cichlids.

Distribution and habitat

thumb|left|210px|[[Pelmatolapia mariae, caught on a hook and line, in Australia: Originally from Africa, the species established feral populations in Australia.]]

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. Native cichlids are largely absent in Asia, except for 9 species in Israel, Lebanon, and Syria (Astatotilapia flaviijosephi, Oreochromis aureus, O. niloticus, Sarotherodon galilaeus, Coptodon zillii, and Tristramella spp.), two in Iran (Iranocichla), and three in India and Sri Lanka (Etroplus and Pseudetroplus). Although no longer present in Europe except as introductions, tilapias are known to have ranged as far north as Italy during the Miocene. 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 (nonpigmented) and blind Lamprologus lethops, 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, 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. 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 in Eritrea encompasses the entire distribution of D. dinicolai, and its temperature ranges from . 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 apparently are 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.

thumb|right|200px|The bumblebee cichlid, [[Pseudotropheus crabro, is specialised in feeding on parasites from the catfish Bagrus meridionalis.]]

Many cichlids are primarily herbivores, feeding on algae (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.

Other cichlids are 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 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. 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 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 In addition to color displays, cichlids employ their lateral lines 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

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 presence of egg spots in a turbid riverine environment would seem particularly beneficial and necessary for intraspecies communication. Facultative selfing may be an adaptive option when a mating partner is unavailable. 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. 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.

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 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. 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 Lake Tanganyika. Courtship in male cichlids follows the establishment of some form of territory, sometimes coupled with building a bower to attract mates.

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). 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 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.), 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.), Chromidotilapia guentheri, and some Aequidens species. This method appears to have evolved independently in several groups of African cichlids. Some of the contributing factors to their diversification are believed to be the various forms of prey processing displayed by cichlid pharyngeal jaw apparatuses. These different jaw apparatuses 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 Lake Apoyo in Nicaragua, Amphilophus zaliosus and its sister species Amphilophus citrinellus display many of the criteria needed for sympatric speciation. In the 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, 52 as endangered, and 106 as critically endangered.

At present, the IUCN only lists 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, H. apogonoides, H. dentex, 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).]]

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. and many others are seriously threatened. 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. Some species have survived in nearby small satellite lakes, or have adapted to the human-induced changes in the lake itself. while the 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.

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 algae 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. Other cichlids preferred by anglers include the oscar, Mayan cichlid (Cichlasoma urophthalmus), and jaguar cichlid (Parachromis managuensis).

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 "angelfish". Other popular or readily available species include the oscar (Astronotus ocellatus), convict cichlid (Archocentrus nigrofasciatus) and discus fish (Symphysodon). Other groups of fishes, such as European 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. 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.

right|thumb|200px|A [[Leucism|leucistic long-finned form of the oscar, A. ocellatus]]

Numerous cichlid species have been 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, leucistic, and xanthistic pigment mutations, including oscars, convict cichlid and Pelvicachromis pulcher. 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 Mikrogeophagus ramirezi have health and fertility problems. Similarly, intentional inbreeding can cause physical abnormalities, such as the notched phenotype in 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.

Congochromis Stiassny & Schliewen 2007
Congolapia Dunz, Vreven & Schliewen 2012
Copadichromis Eccles & Trewavas 1989
Coptodon Gervais 1853
Lugubria Varella, Kullander, Menezes, López-Fernández & Oliveira, 2023
Maylandia Meyer & Foerster 1984
Mazarunia Kullander 1990
Mbipia Lippitsch & Seehausen 1998
Mchenga Stauffer & Konings, 2006
Melanochromis Trewavas, 1935
Mesonauta Günther, 1862
Microchromis Johnson 1975
Microdontochromis Poll 1986
Mikrogeophagus Meulengracht-Madson 1968
Myaka Trewavas 1972
Mylochromis Regan 1920
Naevochromis Eccles & Trewavas 1989
Nandopsis Gill, 1862
Nannacara Regan 1905
Nanochromis Pellegrin 1904
Neochromis Regan 1920
Neolamprologus Colombe & Allgayer 1985
Nimbochromis Eccles & Trewavas 1989
Nyassachromis Eccles & Trewavas 1989
Ophthalmotilapia Pellegrin 1904
Oreochromis Günther 1889
Orthochromis Greenwood 1954
Otopharynx Regan 1920
Oxylapia Kiener & Maugé 1966
Pallidochromis Turner 1994
Parachromis Agassiz 1859
Paracyprichromis Poll 1986
Parananochromis Greenwood 1987
Paraneetroplus Regan 1905
Paratilapia Bleeker, 1868
Paretroplus Bleeker, 1868
Pelmatochromis Steindachner 1894

| style="vertical-align: top; width: 33%;" |

Pelmatolapia Thys van den Audenaerde 1969