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 1,300 and 3,000.
Anatomy and appearanceEdit
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 feeders that capture and process a very wide variety of food items. This is assumed to be one reason why they are so diverse.
The features that distinguish them from the other Labroidei include:
- A single nostril on each side of the forehead, instead of two.
- No bony shelf below the orbit of the eye.
- Division of the lateral line 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.
Kullander (1998) recognizes eight subfamilies of cichlids: the Astronotinae, Cichlasomatinae, Cichlinae, Etroplinae, Geophaginae, Heterochromidinae, Pseudocrenilabrinae, and Retroculinae. A ninth subfamily, Ptychochrominae, was later recognized by Sparks and Smith. Cichlid taxonomy is still debated, and classification of genera cannot yet be definitively given. A comprehensive system of assigning species to monophyletic genera is still lacking, and there is not complete agreement on what genera should be recognized in this family.
As an example of the classification problems, Kullander placed the African genus Heterochromis phylogenetically within neotropical cichlids, although later papers concluded otherwise. Other problems center upon the identity of the putative common ancestor for the Lake Victoria superflock, and the ancestral lineages of Tanganyikan cichlids.
Comparisons between a morphologically-based phylogeny and analyses of gene loci produce differences at the genus level. There remains a consensus that the Cichlidae as a family is monophyletic.
One problem that transformed cichlid taxonomy is related to dentition, which had been used as a classifying characteristic. In many cichlids, tooth shape changes with age, due to wear, and cannot be relied upon. Genome sequencing and other technologies transformed cichlid taxonomy.
Range and habitatEdit
Originally from Africa, the species established feral populations in Australia.
Cichlids are the most species-rich non-Ostariophysan family in freshwaters worldwide. They are most diverse in Africa and South America. It is estimated that Africa alone hosts at least 1,600 species. Central America and Mexico have approximately 120 species, as far north as the Rio Grande in southern Texas. Madagascar has its own distinctive species (Oxylapia, Paratilapia, Paretroplus, Ptychochromis, and Ptychochromoides), only distantly related to those on the African mainland. Native cichlids are largely absent in Asia, except for nine species in Israel, Lebanon and Syria (Astatotilapia flaviijosephi, Oreochromis aureus, O. niloticus, Sarotherodon galilaeus, Tilapia zillii, and Tristramella spp.), one in Iran (Iranocichla), and three in India and Sri Lanka (Etroplus). 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, Mexico, Japan and northern Australia feral populations of cichlids have become established as exotics.
Although most cichlids are found at relatively shallow depths, several exceptions do exist. These include species such as Alticorpus macrocleithrum and Pallidochromis tokolosh down to 150 meters (490 ft) below the surface in Lake Malawi,
Cichlids are less commonly found in brackish and saltwater habitats, though many species tolerate brackish water for extended periods; Cichlasoma 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. Several species of Tilapia, Sarotherodon, and Oreochromis are euryhaline and can disperse along brackish coastlines between rivers. Only a few cichlids, however, inhabit primarily brackish or salt water, most notably Etroplus maculatus, Etroplus suratensis, and Sarotherodon melanotheron. The 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).
With the exception of the species from Cuba and Hispaniola, 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. 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 freshwater, Ptychochromis grandidieri and Paretroplus polyactis are commonly found in coastal brackish water and they are apparently salt tolerant, as is also the case for Etroplus maculatus and E. suratensis from India and Sri Lanka.
Popular cichlids for the aquarium Edit
- African Butterfly Cichlid
- Convict cichlid
- Archocentrus sajica
- Blue Dolphin
- Keyhole Cichlid
- Flag Acara