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Reproduction

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The diversity of habitats occupied by cichlids is matched by the number of mating systems they employ. In fact, the local ecological conditions are an important indicator of the mating system used, which may vary within the same species. The most primitive condition is monogamy, with males and females essentially monomorphic, excepting some coloring details. Courtship rituals and parental care are common among monogamous pairs. Some cichlids are polygynous: males fertilize the eggs of more than one female. In this system, males might defend a territory that females visit to spawn (only once during the season), two females may defend a territory overlapping that of a male (bigamy), or a male may dominate a harem of multiple females. Cichlids also employ polyandry, in which females mate with several males. In one extraordinary case, sex roles are essentially reversed. Sarotherodon melanotheron males nurture eggs and fry in the mouth for 15 days after spawning, while females are capable of spawning just a week later. This creates a situation where the availability of males to brood the eggs is the limiting factor in reproduction. Behavioral studies reveal that male Sarotherodon melanotheron are less aggressive, and more selective, choosing larger females. Next, some cichlids may be promiscuous (polygynandrous).

An intriguing form of promiscuous spawning in some planktivorous cichlids (and at least one non-planktivorous cichlid as well) is termed “lekking,” a Swedish word meaning “to play.” Amazingly, from 5,000 to 50,000 males may congregate during lekking, which occurs over a long breeding season in some cichlids. Some lekking species, such as Copadichromis eucinostomous, migrate inshore and build volcano-like nests out of sand , while others lek in open waters, such as Paracyprichromis brieni. Females then mate with between 4 and 12 males, distributing a few eggs to each. A final mating system, termed “extended family” is found in at least one cichlid species, Neolamprologus multifasciatus. In this scenario, there are colonies of approximately 19 individuals (one to three males, up to five females, and the rest juveniles) with a large dominant male (alpha) and one other male (beta) participating in spawning. A number of individuals in each colony are related (outsiders may occasionally join a colony) and there are overlapping generations within each colony.

In Lake Tanganyika, Neolamprologus tetracanthus illustrates the utility of multiple mating systems in a dynamic environment. In one habitat, where the bottom is barren and predators are abundant, Neolamprologus tetracanthus males remain with their spawning partner to guard the fry. In a different part of the lake, predators are less abundant and populations are larger. There, numerous females establish individual feeding areas and male territories encompass as many as 14 females. The males spawn with each female and exhibit no parental care – an extreme case of polygyny. Numerous other studies support the existence of “plastic” mating strategies among cichlids. St. Peters fishes, of northern Africa, Israel and Jordan, illustrate how distinctions between mating systems are blurred by a single pair of spawning cichlids. Pairs form after a prolonged courtship ritual. After the eggs are fertilized, they may be taken by the male, female, or both as they go their separate ways. The parent that doesn’t take the eggs is free to spawn again. Finally, in harem-forming species and lekking mouth-brooders, smaller or weaker males may attempt to covertly fertilize a female—variously called sneaking, cheating, or parasitic spawning. During lekking males may accomplish this by mimicking females. Parasitic spawning is rare among monogamous species, probably because males and females remain in close proximity while spawning.

Mating System: monogamous ; polyandrous ; polygynous ; polygynandrous (promiscuous) ; cooperative breeder

There are two general modes of cichlid reproduction: substrate brooding and mouthbrooding. Substrate brooding (or nest building) represents the initial (evolutionarily) reproductive strategy, evidenced by the fact that the most primitive species are substrate brooders (See Other Comments). Substrate brooders tend to be monogamous and sexually monomorphic. The egg sacs usually adhere to hard surfaces and the helpless larvae (termed wrigglers), which have large yolk sacs, remain guarded in the nest until they can swim (and are then termed fry). The nests of substrate brooders range from sand castles to sand craters to accumulations of snail shells. Most mouthbrooders are polygynous and sexually dimorphic , although several species are monogamous. The eggs and wrigglers are carried in the mouth of the female , or in monogamous species, both males and females carry larvae in their mouths. As one might expect with such a diverse group of fishes, there is wide variation between the two general patterns described above (See Reproduction: Mating Systems). Many cichlids mate year round and the number of eggs ranges from just a few to several hundred across the family.

Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sequential hermaphrodite; sexual ; fertilization (External ); oviparous

Parental care is likely the most intriguing life history feature of cichlids. Cichlids are well known for their strategy of mouthbrooding, in which the eggs, wrigglers (newly hatched, non-free-swimming young), or fry are carried in the mouth of an individual. In some mouthbrooding species there is no contact with the substrate; the unfertilized eggs are carried in the mouth of the male or female (termed immediate or ovophilic parental care). In others, the eggs are adhered to a substrate, fertilized and taken into the parents mouth after hatching (termed delayed or larvophilic parental care). Female (maternal) mouthbrooding is most common and well known but in at least one species, Sarotherodon melanotheron, the male carries the young (paternal mouthbrooding). In several other species mouthbrooding is biparental, shared by the male and female. Substrate brooders also guard their young, usually in some cooperative parenting system, such as biparental monogamy. Substrate brooding species also expend considerable energy caring for young. The eggs are initially attached to a substrate where they are cared for intensively. The newly hatched wrigglers may be transferred to a newly excavated pit, a patch of leaves, or the rootlets of aquatic vegetation where they are suspended by threads of mucous. The fry move along the substrate feeding on small particles while the parents keep guard.

In both substrate and mouthbrooding species parents use physical movements (termed “calling behaviors”), such as flicking the pelvic fins or jogging the head, when predators approach. These movements serve as cues for fry to retreat, either settling to the substrate near the parent or entering the mouth depending on the type of parental care. Experiments have shown that the level of vulnerability of young is the main determinant of continued parental care, rather than a set time period after hatching. Several other behaviors relating to parental care are described in Development.

Parental Investment: male parental care ; female parental care

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Untitled

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The earliest known cichlid fossils were collected in South America, dating back to the Eocene (57 to 37 million years ago), and in Africa, dating back to the Oligocene (33.7 to 23.8 million years ago). However, the fossil history is poor and it is widely believed that the cichlids, along with other labroid families, arose sometime early in the Cretaceous epoch (144 to 66.4 million years ago). Despite the paucity of fossils, investigators have identified several existing Malagasy and Asian genera as the least derived within the Cichlidae. Researchers have gained a good understanding of the evolutionary biology of cichlids from this discovery. For instance, substrate brooding is considered the ancestral breeding system because it is practiced by the oldest genera in Madagascar and Asia.

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Behavior

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Cichlids are able to communicate by various means: visual, acoustic, chemical and tactile. Visual communication primarily involves color changes and body movements and gestures. At least some cichlids are able to discern colors. Color changes are important in identifying individuals or families, or for communicating aggression, dominance, or sexual state. Typically, the brightest color patterns are associated with aggression. Body movements and gestures are also used to communicate aggression, dominance, or sexual state, and often combine with swimming patterns and color changes to emphasize a particular display. Tactile communication is mainly observed in aggressive males, such as the case of “mouth-fighting.” Tropheus moorii males lock mouths until one individual is pushed to the bottom and flees. In some mouthbrooding species (Simochronis and Tropheus) males often touch the anal region of the female as she begins to expel her eggs, presumably encouraging the female to lay her eggs. Sounds, such as grunts, thumps or purrs have been catalogued for at least 16 cichlid species. Experiments with one cichlid, Archocentrus centrarchus, have revealed that recorded sounds (produced during aggressive displays) evoked an aggressive response. Cichlids are known to use chemical cues to recognize their young in parenting. For example, Amatitlania nigrofasciata and Amphilophus citrinellus are able to discriminate their own small fry from those of other species. The reverse is also true; Amphilophus citrinellus fry are able to distinguish chemical cues given off by their parents. Etroplus maculates and Etroplus suratensis, which feed on fry, use chemical signals to avoid eating fry of the same species. Finally, monogamous pairs of some species need both visual and chemical cues to recognize each other.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: mimicry ; pheromones ; scent marks ; vibrations

Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Conservation Status

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Because many cichlid species are endemic to small geographic areas, they can be threatened relatively easily. Many cichlid species will never be described because they are going extinct so quickly. Such is the case with cichlids of Lake Victoria after the introduction of Nile perch. Nile perch were introduced as a food source (unsupervised) but, as a voracious predator, began to destroy cichlid populations throughout the lake. This has resulted in the largest mass extinction of endemic species in recent times. Conservative estimates are that across the Cichlidae family, 43 cichlids are extinct, five are extinct in the wild, 37 species are critically endangered, 11 species are endangered, 34 species are vulnerable, and one species is at low risk.

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Life Cycle

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Cichlids follow a typical developmental pattern but some species brood the eggs in the mouth while developing. Parents exhibit various behaviors to promote the growth of young, which develop through three distinct stages: eggs, wrigglers (newly hatched, non-free-swimming young), and fry (free swimming but dependent on the parent). At the early stages of development, parents fan the eggs to provide ventilation and remove waste (termed “fanning”). Some species use their mouths to suck away wastes or to remove dead or fungus-ridden eggs (termed “mouthing”). Mouthbrooding species that carry developing eggs in the buccal cavity (mouth) accomplish mouthing and fanning by rolling and swishing the eggs in the mouth (termed “churning”). Finally, several behaviors are related to aiding the young in feeding. Parents may pick up leaf matter and drop it near the young so they may forage on the unexposed side (termed “leaf-lifting”), or dig into the substrate with the fins to expose buried prey (termed “findigging”). Another unusual method of aiding the fry in development is “micronipping,” in which fry feed on mucous secreted from the skin of parents. Micronipping was first discovered in Symphysodon discus, but has since been recorded for several other cichlid species.

Some species of blue tilapia (among others), which are widely used in aquaculture, are susceptible to sex change for a period approximately 30-40 days after hatching by controlling temperature or adding hormones (See Mating Systems). Despite the fact that genetics also influence sex determination, hormones and temperature can overrule genetic determination, creating offspring that are all one sex. Aquaculturists take advantage of this fact to create single sex tanks, thus avoiding overpopulation.

Development - Life Cycle: temperature sex determination

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Comprehensive Description

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The Cichlidae family stands out as an extraordinary example of vertebrate evolution. From the sheer size of the family to the complexity of their ecological interactions and rapid evolution, cichlids provide a unique glimpse of the many factors that promote speciation. The behavioral and physical changes resulting from intense speciation in cichlids is equally impressive. Cichlids demonstrate some of the most unique and intensive parenting in fishes and utilize several different mating systems, from monogamy to polygynandry (See Reproduction). Many feeding behaviors found in cichlids are unique among freshwater fishes (See Behavior and Food Habits). Finally, although the general body plan of cichlids is constant, they come in a dazzling array of shapes, sizes, colors, and dental plans, making them popular with aquarists and aquaculturists (See Physical Description and Economic Importance to Humans).

There are no concrete figures on the number of genera and species in the Cichlidae family because there are still many revisions being made and a considerable number of species are yet to be described. Rough estimates range from 200 to 2000 species and approximately 140 genera, which, after Cyprinidae and Gobiidae, would make them the third largest family of bony fishes. The largest genus is the African Crenicichla with over 100 species. Cichlids inhabit fresh waters, and many species are endemic to isolated lake environments. The fact that no genera occur on more than one continent illustrates the degree of endemism in this family.

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Benefits

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No specific information was found concerning any negative impacts to humans.

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Benefits

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Several cichlid genera are popular aquarium fishes - Cichlasoma, Pterophyllum, Symphysodon, and jewelfishes - because of their mild temperament and ease of breeding in captivity. However, most cichlids are extremely aggressive when kept in small areas and very difficult to breed. Several Cichla species are popular with sport fishermen, especially in Brazil. Cichlids have also been introduced for recreational fisheries or vegetation control.

Some cichlids are used extensively in aquaculture for several reasons. They are a good source of ‘white fish’ and fish products, they lack small bones in the muscle, and some species can grow quite large, allowing for the production of value-added products such as fillets. Most importantly, they feed low on the food chain (aquatic plants and plankton) so the cost of feed is low. Oreochromis and Tilapia are the most extensively farmed cichlids. They are most widely grown in Israel and Asia but cichlid aquaculture has been introduced to many other regions: Egypt (Tilapia), Africa (Oreochromis), Latin America (Astronotus, Cichlasoma and Orechromis), and the Caribbean (Tilapia).

Positive Impacts: pet trade ; food ; research and education; controls pest population

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Associations

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In the Great Lakes of Africa, the number of cichlid species is so large they fill virtually every ecological role within their trophic level, with the exception of primary producers such as photosynthetic algae and benthic arthropods. As one might expect, there is considerable interplay between various cichlid species in terms of predation and food availability. However, cichlids also influence the species of plants and algae that grow in their habitat (top-down control). One example of top-down control is illustrated by the introduction of the piscivorous Nile perch into Lake Victoria. The Nile perch is a voracious predator of small, planktivorous cichlids, which suffered precipitous population decline after the perches’ introduction. Planktivorous cichlids exert considerable predation pressure on zooplankton, and after they were eliminated, the zooplankton community changed drastically, to the point that a new species of zooplankton began invading the lake, Daphnia magna.

Ecosystem Impact: biodegradation ; keystone species ; parasite

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Trophic Strategy

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As a family, cichlids consume virtually every type of food source available in the freshwater habitat they are found. They exhibit numerous modifications of the lips, teeth, jaws and gill rakers depending on the main food source. Although many cichlids are morphologically adapted to a particular food source, they may become generalists depending on availability. Additionally, cichlids consume various types of food depending on their stage of growth. Herbivorous cichlids may browse, scrape, comb, ‘tap’ or suck epiphytic (attached) algae, unicellular algae, and/or clumps of the substrate. Planktivorous cichlids browse throughout the water column on zooplankton and phytoplankton. Piscivorous cichlids feed on whole fish, the fry, larvae, or eggs of mouthbrooding species, and the scales or fins of various fishes. Three species from the genus Cyrtocara (Lake Malawi) use the peculiar technique, termed head-ramming, of shoving their head into the mouth of female mouthbrooders to force the expulsion of eggs, larvae, or fry, which they eat. Cichlids that feed on aquatic insects and other invertebrates use a variety of methods to expose or capture prey. Several species (Labidochromis maculicauda, Tanganicodus irsacae) browse over patches of algae or substrate, picking out individual insects and crustaceans. Lethrinops (Lake Malawi) feed on chironomid larvae by biting into the sandy substrate and filtering the larvae out with their gill rakers. The enlarged lips of some cichlids are used to suck insects out of cracks and crevices, while in others the lips help to feel for prey when browsing over various substrates. In addition to the latter feeding methods, some cichlids have developed swimming patterns allowing them to sneak up on prey or use larger fish for cover. Finally, the teeth of some cichlids are predominantly molars, allowing them to crush and process small and thin-shelled mollusks. (See an illustration of tooth morphology and diversity in fish).

Foraging Behavior: filter-feeding

Primary Diet: carnivore (Piscivore , Eats eggs, Eats body fluids, Eats non-insect arthropods, Molluscivore , Scavenger ); herbivore ; omnivore ; planktivore ; detritivore

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Distribution

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Cichlids are mainly found in the lowland, freshwater areas of tropical and subtropical regions. However, some of the most primitive species, which are found in Madagascar (17 species) and Asia, also inhabit brackish waters. Some other areas with brackish-water species include coastal India and Sri Lanka (three species), and Cuba and Hispaniola (four species). The great majority of cichlids are found in the Great Lakes of East Africa (Lake Malawi, Lake Victoria, and Lake Tanganyika), where between 800 and 2100 species are thought to exist. Nearly all of these species are endemic (evolved in and confined to a particular place) to the lake they inhabit. There are approximately 150 river species in the region as well. The remaining distribution includes South America (approximately 290 species), Central America and Mexico (approximately 95 species), North America (one species), and the Middle East - Iran, Syria, Israel and Palestine (five species).

Cichlids have been widely introduced, either deliberately for aquaculture or accidentally through the aquarium trade (Lever, 1996). For instance, in the United States there is only one native species, the Rio Grande cichlid, but 44 species have been introduced. Florida has proven ideal for many exotic cichlids like the oscar, peacock cichlid, and Jack Dempsey, due to its warm climate and abundant water.

Biogeographic Regions: nearctic (Introduced , Native ); palearctic (Introduced , Native ); oriental (Introduced , Native ); ethiopian (Native ); neotropical (Native )

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Habitat

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Most cichlids inhabit lakes or the sluggish areas of rivers but there are a few species adapted to swift flowing streams, including some Crenicichla species. Species in the genera Teleocichla and Retroculus, distributed in the highlands of Brazil and New Guinea, are also rheophilic (prefer flowing waters). In lakes there are few habitats cichlids do not occupy and there is an abundance of species filling virtually every ecological niche in some areas. For example, deepwater cichlids from Lake Tanganyika, Africa are able to survive in the permanently deoxygenated water layers for short periods. Individuals from the genera Tilapia and Oreochromis are also able to withstand low oxygen concentrations. Finally, some cichlids are tolerant of brackish waters. Oreochromis, Sarotherodon, and Tilapia are able to migrate along coastlines between rivers and some species, such as Oreochromis mossambicus, have become established in brackish and marine waters.

Habitat Regions: tropical ; saltwater or marine ; freshwater

Aquatic Biomes: pelagic ; benthic ; reef ; lakes and ponds; rivers and streams; coastal ; brackish water

Other Habitat Features: agricultural ; estuarine

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Life Expectancy

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The lifespan of many wild cichlids is unknown. However, in aquaria they are relatively long-lived, about 10 years on average. Several can reach up to 18 years in captivity, suggesting that at least some cichlids have considerably long lifespans.

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Morphology

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Most cichlids are distinguished from all other freshwater fish by the existence of two unique features: a single opening of the nostrils and an interrupted lateral line. The two exceptions are Teleogramma and Gobiocichla, which have a continuous lateral line. The anal fin spines usually number three, but some species have four to nine anal fin spines and the Asian genus Etroplus has between 12 and 15. In general cichlids are relatively small in size but Boulengerochropmis microlepis and the Neotropical Cichla temensis reach approximately a meter in length. (Click here to see a fish diagram).

Superficially, there seem to be major differences in body shape across the Cichlidae family, with body shapes ranging from tubular, to perch-like, to disk-like, depending on habitat. For instance, Teleogramma, Gobiocichla, Teleocichla and Retroculus inhabit flowing waters and have elongate, tubular bodies, small, deeply imbedded scales and enlarged and thickened pelvic fins. Freshwater angelfish have extended dorsal and anal fins and discus fishes, have compressed, disc-like bodies. Finally, fast moving piscivorous cichlids, such as Crenicichla, Diplotaxodon, and Rhamphochromis, are elongate and streamlined. However, the fundamental cichlid morphology - position of the fins, arrangement of the jaws, and nature of the scales – remains consistent despite the wide variation in body forms.

The various components of the mouth together comprise some of the most intriguing physical features of cichlids. To begin with, the lips of several cichlid species are large and puffy, probably to help form a seal against irregular surfaces, so food can be sucked up (as in some detrivores). The outer jaw contains up to seven rows of teeth, which decrease in size moving toward the throat. The ancestral tooth shape is conical, but there are numerous variations depending on the diet of the fish. Some examples include stout, knife-like teeth for tearing up prey, teeth at right angles or in broad, file-like bands for ripping off the scales or flesh of other fish, flattened teeth with cusps for feeding on clumps of benthic algae, or brush-like teeth used to comb epiphytes (algae that grows on other algae) off filamentous algae. Most common, however, are flat, molar-like teeth, which come in a wide variety of shapes and are often mixed with other types of teeth. Next are the jaws, which are composed of a complex cage of bones around the skull connected by numerous muscles. The plasticity of the jaws in carnivorous cichlids allows individuals to create negative pressure, effectively sucking the prey toward them, or to extend one part of the jaw independent of the other, so individuals can grasp prey below them. The gill rakers lie just behind the jaws and vary considerably depending on intended prey. In piscivorous cichlids, the gill rakers are short, sturdy and sharp while planktivores and detrivores have numerous, long, thin and tightly packed gill rakers for filtering out food particles. Other cichlids have true teeth on the gill rakers, which aid in the processing of prey. Finally, the pharyngeal jaw apparatus contains yet another set of teeth, which, as with the outer jaws, contain a wide variety of tooth types depending on the diet. The pharyngeal jaw also frees up the outer jaw from chewing, allowing more prey to be captured while the previous meal is being processed (See Food Habits for more details).

Sexual dimorphism occurs in some cichlids, and is most common in polygynous mouthbrooders and harem-forming species. Typically, males are larger than females and males exhibit more elaborate coloration. An extreme case of size dimorphism can be found in the harem-forming ,Neolamprologus callipterus. Males can be up thirty times the size of the miniscule females; this is the largest margin known for any vertebrate animal by which males outsize females. Apistogramma also exhibits sexual dimorphism, as males are strikingly colored and lavishly ornamented with elongated filaments on the spines of their dorsal and anal fins, and on the tails and pelvic fins. Most monogamous cichlids are virtually indistinguishable, although males are larger than females on average. During spawning, however, the foreheads of males swell in some species, such as Midas cichlids, or the sexes may take on different coloration (dichromatic). In an odd departure from the usual sexual dimorphism (with males being more colorful), female convict cichlids display gold colors on the lower half of the midsection of the body (where the egg sac is located) to attract males. Since this discovery, numerous examples of “reverse dichromatism” have been found in other cichlid species.

Other Physical Features: ectothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike; male larger; sexes colored or patterned differently; female more colorful; male more colorful; sexes shaped differently; ornamentation

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Associations

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Many large cichlids prey on smaller members of their family or specifically feed in eggs, larvae, or fry. Investigators have also observed newly independent juveniles preying on young of the same or related species. These predation pressure help explain the evolution of intense parental care in cichlids. Introduced species, such as Nile perch, have proven disastrous for many endemic cichlids, even causing the extinction of some species (See Ecosystem Roles and Conservation Status). Humans have also exploited cichlids throughout their range for centuries.

Known Predators:

  • fish (Actinopterygii)
  • humans (Homo sapiens)

Anti-predator Adaptations: mimic; cryptic

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Jonna, R. 2004. "Cichlidae" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html
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Cichlid

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Cichlids /ˈsɪklɪdz/[1] are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, Labroidei, along with the wrasses (Labridae), in the order Perciformes[2] but molecular studies have contradicted this grouping.[3] The closest living relatives of cichlids are probably the convict blennies 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.[4] This family is both large and diverse. At least 1,650 species have been scientifically described,[5] making it one of the largest vertebrate 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.[6]

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.[7][8] Cichlids have the largest number of endangered species among vertebrate families, most in the haplochromine group.[9] Cichlids are particularly well known for having evolved rapidly into many closely related but morphologically diverse species within large lakes, particularly Tanganyika, Victoria, Malawi, and Edward.[10][11] Their diversity in the African Great Lakes is important for the study of speciation in evolution.[12] Many cichlids introduced into waters outside of their natural range have become nuisances.[13]

All cichlids have some form of parental care for their eggs and fry. That parental care may come in the form of guarding the eggs and fry or it may come in the form of mouthbrooding.

Anatomy and appearance

"
Relationships within the Labrodei[2]

Cichlids span a wide range of body sizes, from species as small as 2.5 cm (0.98 in) in length (e.g., female Neolamprologus multifasciatus) to much larger species approaching 1 m (3.3 ft) 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).[7] 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.[14]

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.[7]

The features that distinguish them from the other families in Labroidei include:[15]

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

Taxonomy

Kullander (1998) recognizes eight subfamilies of cichlids: the Astronotinae, Cichlasomatinae, Cichlinae, Etroplinae, Geophaginae, Heterochromidinae, Pseudocrenilabrinae, and Retroculinae.[16] A ninth subfamily, Ptychochrominae, was later recognized by Sparks and Smith.[17] 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.[18]

As an example of the classification problems, Kullander[19] 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 Tanganyikan cichlids.

Comparisons[20] between a morphologically-based phylogeny[21] and analyses of gene loci[22] produce differences at the genus level. There remains a consensus that the Cichlidae as a family is monophyletic.[23][24]

In cichlid taxonomy, dentition was formerly used as a classifying characteristic. However, this was complicated by the fact that in many cichlids, tooth shape changes with age, due to wear, and cannot be relied upon. Genome sequencing and other technologies transformed cichlid taxonomy.[25]

Distribution and habitat

"
Pelmatolapia mariae, caught on a hook and line, in Australia. Originally from Africa, the species established feral populations in Australia.[26]

Cichlids are one of the largest vertebrate families in the world. They are most diverse in Africa and South America. Africa alone is estimated to host at least 1,600 species.[18] Central America and Mexico have about 120 species, as far north as the Rio Grande in southern Texas. Madagascar has its own distinctive species (Katria, Oxylapia, Paratilapia, Paretroplus, Ptychochromis, and Ptychochromoides), only distantly related to those on the African mainland.[15][27] 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).[18] 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 and Hispaniola. Europe, Australia, Antarctica, and North America north of the Rio Grande drainage have no native cichlids, although in Florida, Hawaii, Japan, northern Australia and elsewhere, feral populations of cichlids have become established as exotics.[26][28][29][30][31][32][33]

Although most cichlids are found at relatively shallow depths, several exceptions do exist. The deepest known occurrence are Trematocara at more than 300 m (980 ft) below the surface in Lake Tanganyika.[34] Others found in relatively deep waters include species such as Alticorpus macrocleithrum and Pallidochromis tokolosh down to 150 m (490 ft) below the surface in Lake Malawi,[35][36] and the whitish (nonpigmented) and blind Lamprologus lethops, which is believed to live as deep as 160 m (520 ft) below the surface in the Congo River.[37]

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.[7] Several species of Tilapia, Sarotherodon, and Oreochromis are euryhaline and can disperse along brackish coastlines between rivers.[18] Only a few cichlids, however, inhabit primarily brackish or salt water, most notably Etroplus maculatus, Etroplus suratensis, and Sarotherodon melanotheron.[38] 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 29 to 45 °C (84 to 113 °F).[39]

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: Africa-South America and India-Madagascar.[40] 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 they are apparently salt tolerant,[41][42] as is also the case for Etroplus maculatus and E. suratensis from India and Sri Lanka.[43][44]

Ecology

Feeding

Within the cichlid family, there are carnivores, herbivores, omnivores, planktivores, and detritivores, meaning Cichildae encompasses essentially the full range of food consumption possible in the animal kingdom. Various species have morphological adaptations for specific food sources,[45] but most cichlids will 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 differs greatly between the two categories. Piscivorous cichlids will 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 in order to expel her young and eat them.[46] 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.[47]

"
The bumblebee cichlid, Pseudotropheus crabro, is specialised in feeding on parasites from the catfish Bagrus meridionalis.[48]

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; 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.[49] 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.[50][51][52][53] 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,[54][55][56] along with the death-mimicking behaviour of Nimbochromis and Parachromis species, which lay motionless, luring small fish to their side prior to ambush.[57][58]

This variety of feeding styles has helped cichlids to inhabit similarly varied habitats. Its pharyngeal teeth (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,[59] coinciding with temporal proximity to mating. Displays of ritualized aggression in cichlids include a remarkably rapid change in coloration, during which a successfully dominant[59] territorial male assumes a more vivid and brighter coloration while a subordinate or “non-territorial” male assumes a dull-pale coloration.[60] 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.[61] Male cichlids are very territorial due to the pressure of reproduction, males establish their territory and social status by physically driving out[62] challenging males (novel intruders)[63] through lateral displays (parallel orientation, uncovering gills),[64] biting, or mouth fights (head-on collisions of ajar 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 become a contest for resources[62] (mates, territory, food). Female cichlids prefer to mate with a successfully alpha male with vivid coloration, whose territory has food readily available.

Mating

Cichlids mate either monogamously or polygamously.[7] 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.[7][65]

Most adult male cichlids, specifically in the Haplochromini tribe of cichlids, exhibit a unique pattern of oval-shaped, color dots on their anal fins. These phenomena are known as egg-spots and aid in the mouthbrooding mechanisms of cichlids. The egg-spots consist of carotenoid based pigment cells, which indicates a high cost to the organism, when considering that fish are not able to synthesize their own carotenoids.[66]

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.[67] 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.[66]

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, it was hypothesized that the true egg spots evolved in the common ancestor of the Astatoreochromis-lineage and the modern Haplochrominis. This ancestor was most likely riverine in origin, based on the most parsimonious representation of habitat type in the cichlid family.[68] The presence of egg-spots in a turbid riverine environment, would seem particularly beneficial and necessary for intra-species communication.[68]

There are two pigmentation genes that are found to be associated with egg-spot patterning and color arrangement. These are fhl2-a and fhl2-b, which are paralogs.[67] 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 SINE (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[67]

Brood care

"
A substrate brooding female managuense cichlid, Parachromis managuense, guards a clutch of eggs in the aquarium.

Cichlids have highly organized breeding activities.[18] All species show some form of parental care for both 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.[69][70][71] 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.[72] Several cichlids, including discus (Symphysodon spp.), some Amphilophus species, Etroplus, and Uaru species, feed their young with a skin secretion from mucous glands.[7][73]

The species Neolamprologus pulcher uses a cooperative breeding system, in which one breeding pair has many helpers which are subordinate to the dominant breeders.

Parental care falls into one of four categories:[73] substrate or open brooders, secretive cave brooders (also known as guarding speleophils[74]), and at least two types of mouthbrooders, ovophile mouthbrooders and larvophile mouthbrooders.[75]

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 and leading the fry while foraging. However, both sexes are able to perform the full range of parenting behaviours.[75]

Cave brooding

"
A female Cyphotilapia frontosa mouthbrooding fry, which can be seen looking out her mouth

Secretive cave-spawning cichlids lay their eggs in caves, crevices, holes, or discarded mollusc shells, frequently attaching the eggs to the roof of the chamber. Examples include Pelvicachromis spp., Archocentrus spp., and Apistogramma spp.[73] 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.[75]

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, Lake Tanganyika 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.[7][73] 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 Sarotherodon melanotheron[76]), Chromidotilapia guentheri, and some Aequidens species.[7][75][77] This method appears to have evolved independently in several groups of African cichlids.[18]

Speciation

"
Cichlids of the African rift lake system evolved from an original hybrid swarm.[78]

Cichlids provide scientists with a unique perspective of speciation, having become extremely diverse in the more recent geological past. It is widely believed that one of the contributing factors to their diversification are 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, planktivores, piscivores, and insectivores.[79] 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 life cycle, they most likely spawn with like individuals. This can reinforce the jaw morphology and given enough time, create new species.[80] 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.[81] In the African rift lake system, cichlid species in numerous distinct lakes evolved from a shared hybrid swarm.[78]

Population status

In 2010, the International Union for Conservation of Nature classified 184 species as vulnerable, 52 as endangered, and 106 as critically endangered.[82] At present, the IUCN only lists Yssichromis sp. nov. "argens" as extinct in the wild, and six species are listed as entirely extinct, but it is acknowledged that 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 in the small chance that tiny –but currently unknown– populations survive).[82]

Lake Victoria

"
Haplochromis thereuterion has declined, but still survives in low numbers.[83]

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.[84]

By far the largest Lake Victoria group are the haplochromine cichlids, with more than 500 species, but at least 200 of these (approximately 40%) have become extinct,[85][86][87] and many others are seriously threatened.[88] Initially it was feared that the percentage of extinct species was even higher,[89] but some species have been rediscovered after the Nile perch started to decline in the 1990s.[86][90] Some species have survived in nearby small satellite lakes,[90] or in refugia among rocks or papyrus sedges (protecting them from the Nile perch),[91] or have adapted to the human-induced changes in the lake itself.[86][87] 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,[92] 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.[86]

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 lakes.[84]

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 1,500,000 t (1,500,000 long tons; 1,700,000 short tons) annually, with an estimated value of US$1.8 billion,[93] 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.[84]

Game fish

Many large cichlids are popular game fish. The peacock bass (Cichla species) of South America is one of the most popular sportfish. It was introduced in many waters around the world. In Florida, this fish generates millions of hours of fishing and sportfishing revenue of more than US$8 million a year.[94] Other cichlids preferred by anglers include the oscar, Mayan cichlid (Cichlasoma urophthalmus), and jaguar guapote (Parachromis managuensis).[94]

Aquarium fish

"
The discus, Symphysodon spp., has been popular among aquarium enthusiasts.

Since 1945, cichlids have become increasingly popular as aquarium fish.[7][73][75][95][96][97][98]

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).[7]

Hybrids and selective breeding

"
The "red Texas" cichlid is not a Texas cichlid (Herichthys cyanoguttatus) but an intergeneric hybrid of Herichthys and Amphilophus parents.

Some cichlids readily hybridize with related species, both in the wild and under artificial conditions.[99] Other groups of fishes, such as European cyprinids, also hybridize.[100] Unusually, cichlid hybrids have been put to extensive commercial use, in particular for aquaculture and aquaria.[8][101] 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.[8]

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 synspillus With a triangular-shaped mouth, an abnormal 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".[102] 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.[103] The popularity of the flowerhorn cichlid declined in 2004.[104] Owners released many specimens into the rivers and canals of Malaysia and Singapore, where they threaten endemic communities.[105]

"
A 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.[7][106][107] Other cichlids have been bred for albino, leucistic, and xanthistic pigment mutations, including oscars, convict cichlid and Pelvicachromis pulcher.[7][73] Both dominant and recessive pigment mutations have been observed.[108] In convict cichlids, for example, a leucistic coloration is recessively inherited,[109] while in Oreochromis niloticus niloticus, red coloration is caused by a dominant inherited mutation.[110]

This selective breeding may have unintended consequences. For example, hybrid strains of Mikrogeophagus ramirezi have health and fertility problems.[111] Similarly, intentional inbreeding can cause physical abnormalities, such as the notched phenotype in angelfish.[112]

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.[15]

Images of cichlids

References

  1. ^ Cichlid is frequently mispronounced in the pet trade as if spelled "chicklid" /ˈɪklɪd/, presumably from confusion with names like Chiclets, and with Italian words like cioppino and ciao that start with ci- and the sound //.
  2. ^ a b Stiassny, M.L.J.; Jensen, J.S. (1987). "Labroid intrarelationships revisited: morphological complexity, key innovations, and the study of comparative diversity". Bulletin of the Museum of Comparative Zoology. 151: 269–319.
  3. ^ Wainwright, Peter C.; et al. (2012). "The Evolution of Pharyngognathy: A Phylogenetic and Functional Appraisal of the Pharyngeal Jaw Key Innovation in Labroid Fishes and Beyond". Systematic Biology. 61 (6): 1001–1027. doi:10.1093/sysbio/sys060. PMID 22744773.
  4. ^ J. S. Nelson; T. C. Grande; M. V. H. Wilson (2016). Fishes of the World (5th ed.). Wiley. p. 752. ISBN 978-1-118-34233-6.
  5. ^ "List of Nominal Species of Cichlidae, in Froese, Rainer, and Daniel Pauly, eds. (2012). FishBase". February 2012.
  6. ^ Stiassny, M., G. G. Teugels & C. D. Hopkins (2007). The Fresh and Brackish Water Fishes of Lower Guinea, West-Central Africa – Vol. 2. Musée Royal de l'Afrique Centrale. p. 269. ISBN 978-90-74752-21-3.CS1 maint: multiple names: authors list (link)
  7. ^ a b c d e f g h i j k l m Loiselle, P.V. (1994). The Cichlid Aquarium. Tetra Press. ISBN 978-1-56465-146-4.
  8. ^ a b c Kosswig, Curt (June 1963). "Ways of Speciation in Fishes". Copeia. 1963 (2): 238–244. doi:10.2307/1441338. JSTOR 1441338.
  9. ^ Reid, G. M. (December 1990). "Captive breeding for the conservation of cichlid fishes". Journal of Fish Biology. 37: 157–166. doi:10.1111/j.1095-8649.1990.tb05031.x.
  10. ^ Salzburger W.; Mack T.; Verheyen E.; Meyer A. (2005). "Out of Tanganyika: Genesis, explosive speciation, key-innovations and phylogeography of the haplochromine cichlid fishes" (PDF). BMC Evolutionary Biology. 5 (17): 17. doi:10.1186/1471-2148-5-17. PMC 554777. PMID 15723698.
  11. ^ Snoeks, J. (ed.) (2004). The cichlid diversity of Lake Malawi/Nyasa/Niassa: identification, distribution and taxonomy. Cichlid Press. ISBN 978-0-9668255-8-9.CS1 maint: extra text: authors list (link)
  12. ^ Kornfield, Irv; Smith, Peter (November 2000). "African Cichlid Fishes: Model Systems for Evolutionary Biology". Annual Review of Ecology and Systematics. 31: 163–196. doi:10.1146/annurev.ecolsys.31.1.163.
  13. ^ Gulf States Marine Fisheries Commission. "Fact sheet for Oreochromis mossambicus (Peters, 1852)". Gulf States Marine Fisheries Commission. Archived from the original on 18 August 2007. Retrieved 20 October 2006.
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Cichlid: Brief Summary

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Cichlids /ˈsɪklɪdz/ are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, Labroidei, along with the wrasses (Labridae), in the order Perciformes but molecular studies have contradicted this grouping. The closest living relatives of cichlids are probably the convict blennies 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. This family is both large and diverse. At least 1,650 species have been scientifically described, making it one of the largest vertebrate 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, oscars, and discus. Cichlids have the largest number of endangered species among vertebrate families, most in the haplochromine group. Cichlids are particularly well known for having evolved rapidly into many closely related but morphologically diverse species within large lakes, particularly Tanganyika, Victoria, Malawi, and Edward. 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 have some form of parental care for their eggs and fry. That parental care may come in the form of guarding the eggs and fry or it may come in the form of mouthbrooding.

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