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.
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
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.
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
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.
No specific information was found concerning any negative impacts to humans.
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
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
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
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 )
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
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.
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
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:
Anti-predator Adaptations: mimic; cryptic
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
