Cichlids are fish from the family Cichlidae in the order Perciformes. The family Cichlidae, a major family of perciform fish, is both large and diverse. There are at least 1300 scientifically described species, making it one of the three largest vertebrate families. Numerous new species are discovered annually, and many species remain undescribed. The actual number of species is therefore unclear, with estimates varying between 1300 and 3000 species, and one source suggesting 1900 species. Cichlids span a wide range of body sizes, from species as small as 2.5 centimetres (1.0 in) in length (e.g. female Neolamprologus multifasciatus ) to much larger species approaching 1 metre (3 ft) in length (e.g. Boulengerochromis and Cichla). As a group, cichlids exhibit a similarly wide diversity of body shapes, ranging from strongly laterally compressed species (such as Altolamprologus, Pterophyllum, and Symphysodon) through to species that are cylindrical and highly elongate (such as Julidochromis, Teleogramma, Teleocichla, Crenicichla, and Gobiocichla). Generally, however, cichlids tend to be of medium size, ovate in shape and slightly laterally compressed, and generally very similar to the North American sunfishes in terms of morphology, behaviour, and ecology.
Many cichlids, particularly the tilapias, are important food fishes, while others are valued game fish (eg. Cichla species). Many species, including the angelfish, oscars, and discus, are also highly valued in the aquarium trade. Cichlids are also the family of vertebrates with the largest number of endangered species, most of these found in the haplochromine group. Cichlids are particularly well known for having evolved rapidly into a large number of closely related but morphologically diverse species within large lakes, particularly Tanganyika, Victoria, Malawi, and Edward. The diversity of cichlids in the African Great Lakes is important for the study of speciation in evolution. Many cichlids that have been accidentally or deliberately released into freshwaters outside of their natural range have become nuisance species, for example tilapia in the southern United States.
The particular features of cichlids that distinguish them from the other Labroidei include:
As an example of the extant problems in Cichlid taxonomy, Kullander published a phylogeny of the Cichlidae (details of which can be found here) in which the African genus Heterochromis ended up being placed phylogenetically within Neotropical Cichlds, although later papers arrived at different conclusions. Other extant problems (mentioned in the following paragraph) centre upon the identity of the putative common ancestor for the Lake Victoria superflock, and the precise ancestral lineages of the Tanganyikan Cichlids. However, the research is active and intensive (see below for just two of many recent papers), with new papers expected in the immediate future that may resolve some of the outstanding questions.
The paper Multilocus Phylogeny of Cichlid Fishes (Pisces: Perciformes): Evolutionary Comparison of Microsatellite and Single-Copy Nuclear Loci by Streelman, Zardoya, Meyer and Karl (1998) (Mol. Biol. Evol. 15(7):798–808. 1998, paper available as PDF here) provides comparisons between the phylogeny (due to Stiassny, 1991) as determined using morphological characteristics, and two maximum-pasrimony bootstrap consensus trees based upon analyses of two different gene loci, along with majority-rule trees and other similar phylogenetic trees based upon assorted gene locus analyses. There are some extant differences between the assorted trees at the genus level that require resolution, though the consensus from the various nuclear and mitochondrial DNA analyses in this and other papers is that the Cichlidae as a family is monophyletic. Further insights into the attractiveness of Cichlid taxonomy as a fertile area of research is given by the paper The species flocks of East African cichlid fishes: recent advances in molecular phylogenetics and population genetics by Salzburger and Meyer (Naturwissenschaften (2004) 91:277–290, paper available as PDF here), in which the advances made in the analysis of the phylogeny of the Lake Victoria superflock (among other East African Cichlids) is discussed in depth.
One problem that resulted in a major upheaval of Cichlid taxonomy was highlighted by Dr Humphrey Greenwood of the Natural History Museum, London, in a paper in 1977 (cited in TFH magazine, August 1977, with a follow up letter by Dr Greenwood in the November 1977 issue complaining about poor reportage of his work). Dentition (characteristics of tooth shape and arrangement) had been used prior to this date as classifying characteristics, which Greenwood demonstrated was invalid upon phylogenetic grounds because in many Cichlid species, dentition is an environmentally plastic characteristic (tooth shape changes in numerous species with age, due to wear etc), and cannot be relied upon universally across the family as a diagnostic characteristic upon which to base phylogenetic judgements. It is in the light of this that Cichlid taxonomy has undergone major revisions in the 30-plus years since, with the advent of genome sequencing and other technologies adding to the ever-growing body of data resulting in the still-fluid state of Cichlid taxonomy at the genus level.
Cichlids are the most species-rich non-Ostariophysan family in freshwaters worldwide. They are mainly freshwater fish that are most diverse in Africa and South America. It is estimated that there will be at least 1600 species in Africa alone when all are discovered and described. Substantial numbers are also found in Central America from Panama to the Mexican portion of North America, with approximately 120 species, as far north as the Rio Grande in southern Texas, and Madagascar has its own distinctive fauna of cichlids phylogenetically only distantly related to those on the African mainland. Endemic cichlids are largely absent in Asia except for four species in the Jordan Valley in the Middle East, one in Iran, and three in India and Sri Lanka. There are three species found in Cuba and Hispaniola. Europe, Australia, Antarctica, and North America north of the Rio Grande River drainage, do not have any native cichlids, although where environmental conditions are suitable, for example in Florida, Mexico (which also has several native species), Japan and northern Australia, feral populations of cichlids have become established as exotics.
Cichlids are largely freshwater fish and are less commonly found in brackish and salt water habitats, though many species will tolerate brackish water for extended periods; Cichlasoma urophthalmus, for example, is equally at home in freshwater marshes and mangrove swamps, and can be found living and breeding in salt water environments such as the mangrove belts around barrier islands. Several species of tilapias (species of Tilapia, Sarotherodon, and Oreochromis) are euryhaline and can disperse along some brackish coastlines between rivers. Only a few cichlids, however, are found primarily in brackish or salt water, most notably Etroplus maculatus, Etroplus suratensis, and Sarotherodon melanotheron.
Cichlids are astonishingly diverse in terms of diet. Many are primarily herbivores feeding on algae (e.g. Petrochromis) and plants (e.g. Etroplus suratensis) and small animals, particularly invertebrates, are only a small part of their diet. Some cichlids are detritivores and eat all types of organic material; among these species are the tilapiines of the genera Oreochromis, Sarotherodon, and Tilapia.
Other cichlids are predatory and eat little if any 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 specialised snail-eater, while Pungu maclareni feeds on sponges. A number of cichlids feed on other fish, either whole or in part. Crenicichla are stealth-predators that lunge at small fish that pass by their hiding places, while Rhamphochromis are open water pursuit predators that chase down their prey. Paedophagous cichlids such as the Caprichromis species eat other species' eggs or young (in some cases ramming the heads of mouthbrooding species to force them to disgorge their young). Among the more unusual feeding strategies are those of Corematodus spp., Docimodus evelynae, Plecodus, Perissodus and Genyochromis species, which feed on scales and fins of other fishes, a behaviour known as lepidophagy along with the death mimicking behaviour of Nimbochromis and Parachromis species, which lay motionless, luring small fish to their side prior to ambush.
Scientists believe it is this wide adaptability of feeding styles that has helped cichlids to inhabit such a wide range of habitats. It is largely the pharyngeal teeth (teeth in the throat) that allows the cichlids so many 'niche' feeding behaviours, i.e. the jaws may be used to hold or pick food, while the pharyngeal teeth are used to crush what was harvested.
Parental care falls into one of four categories:Substrate or open brooders, secretive cave brooders (also known as guarding speleophils), and at least two types of mouthbrooding, ovophile mouthbrooding and larvophile mouthbrooding.
Open or substrate brooding cichlids lay their eggs in the open on rocks, leaves or logs. Examples of open brooding cichlids include Pterophyllum, Symphysodon spp and Anomalochromis thomasi. In general, brooding biparental substrate brooding cichlids usually engage in differing roles with regard to protection and raising of the fry. Most commonly, the male parent patrols the pair's territory and repels intruders, while females more intensively tend the brood, fanning water over the eggs, removing infertile eggs and leading the school of fry while foraging. Despite this, both sexes are able to perform the full range of parenting behaviours. Secretive cave spawning cichlids lay their eggs in caves, crevices, holes or discarded mollusc shells (see also: shell brooding cichlids), frequently attaching the eggs to the roof of the chamber. Examples include Pelvicachromis spp., Archocentrus spp and Apistogramma spp. Communication between free-swimming fry and parents of both open and cave spawning cichlids has been observed for a number of cichlids in captivity and in the wild. Frequently this communication is based on body movements, such as shaking and pelvic fin flicking. In addition, parental substrate brooding cichlids assist in finding food resources for their fry. Parental behaviours such as leaf-turning, and fin-digging have been observed for a number of neotropical cichlid species.
Communal parental care, where multiple monogamous pairs care for a mixed school of young have also been observed for a number of cichlid species including: Amphilophus citrinellus, Etroplus suratensis and Tilapia rendalli. Comparably, the fry of Neolamprologus brichardi, a species that commonly lives in large groups, are protected not only by the adults, but also by older juveniles from previous spawns.
Ovophile mouthbrooders incubate their eggs in their mouths as soon as they are laid, and frequently continue to brood free-swimming fry in their mouths for several weeks. Examples of ovophile mouthbrooding cichlids include many of the cichlids endemic to the Rift Valley lakes (Lake Malawi, Lake Tanganyika and Lake Victoria) in east Africa eg: Maylandia, Pseudotropheus and Tropheus along with some south american cichlids such as Geophagus steindachneri. Larvophile mouthbrooding species lay the eggs in the open, or in a cave and upon hatching take the larvae into the mouth. Examples include some variants of Geophagus altifrons, some Aequidens, Gymnogeophagus and Satanoperca species. Regardless of whether eggs or larvae are subject to mouthbrooding, the vast majority of mouthbrooding cichlids are maternal mouthbrooders, that is the female mouthbroods the young. In the eretmodine cichlids (genera Spathodus, Eretmodus and Tanganicodus), some Sarotherodon species, Chromidotilapia guntheri and some Aequidens species, however, mouthbrooding is practiced by both the male and the female. Paternal mouthbrooding, though rare, is also known to occur in the family eg. Sarotherodon melanotheron. This method is common and appears to have evolved independently in several groups of African cichlids.
In addition to being food fish, many large cichlids also make good game fish. The strong, hard-fighting peacock bass (Cichla species) of South America is one of the most popular sportfish. It was intentionally released in many waters around the world. In Florida, this fish generates millions of hours of fishing and anglers' spendings of more than US$8 million a year. Other cichlids preferred by anglers include the oscar, Mayan cichlid (Cichlasoma urophthalmus), and jaguar guapote (Parachromis managuensis).
Since 1945, cichlids have become increasingly popular as aquarium fish. Cichlids are ideally suited as aquarium fish as many are small to medium-sized, easy to feed with a range of prepared fish foods, breed readily, and practice brood care, in captivity.
The most commonly encountered species in retail aquariums 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 of cichlids include the oscar (Astronotus ocellatus), convict cichlid (Archocentrus nigrofasciatus) and discus (Symphysodon spp.).
Species of cichlid can be kept in aquariums with other fish, however, many cichlids are predatory towards smaller fish. Conversely, some cichlids, such as Apistogramma or Julidochromis spp., can be timid in the aquarium. In such cases the use of dither fish is recommended.
Some cichlids have been found to hybridise with closely related species quite readily, both in the wild and under artificial conditions. This is not particularly unusual, having been observed among other groups of fishes, such as European cyprinids. What is unusual is the extent to which cichlid hybrids have been put to commercial use, in particular as food fish and as aquarium fish. The red strain of tilapia hybrid, for example, is often preferred in aquaculture as they have faster growth rates. Tilapia hybridisation is also used to produce all-male populations to control stock density and prohibit reproduction in ponds.
The most ubiquitous aquarium hybrid is perhaps the blood parrot cichlid which is a cross of several species especially those from genus Amphilophus. With a beak-shaped mouth, an abnormal spine, and an occasionally missing caudal fin (known as the "love heart" parrot cichlid), the fish has caused controversy among aquarium enthusiasts. Some has called blood parrot cichlid "the Frankenstein monster of the fish world." Another notable hybrid, the flowerhorn cichlid, was very popular in some parts of Asia from 2001 until late 2003 and is believed to bring good luck to its owner. The popularity of the flowerhorn cichlid declined in 2004, resulting in many flowerhorn cichlids being released into the rivers and canals of Malaysia and Singapore where they pose a threat to endemic animal communities.
Numerous cichlid species have also been the subject of selective breeding programmes to develop new ornamental strains for the aquarium trade. The most intensive selective breeding programs have involved angelfish and discus and many mutations that effect both colouration and finnage are known. Many other cichlids have been selecively bred for albino, leucistic and xanthistic pigment mutations including oscars, convicts and Pelvicachromis pulcher. Both dominant and recessively inherited pigment mutations have been observed for cichlids. In convict cichlids, for example, a leucistic colouration is recessively inherited, while in Oreochromis niloticus niloticus red colouration is caused by an dominantly inherited mutation.
These efforts at selectively breeding may, however, have unintended consequences. For example, some selectively bred strains of Mikrogeophagus ramirezi have health and fertility problems. Similarly, the inbreeding involved in selective breeding programmes can cause severe physical abnormalities such as the notched phenotype in angelfish.