Cichlid

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 a large number of 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. 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). Generally, however, cichlids tend to be of medium size, ovate in shape, and slightly laterally compressed, and generally similar to the North American sunfishes in morphology, behavior, and ecology. Cichlids share a single key trait: the fusion of the lower pharyngeal bones into a single tooth-bearing structure. A complex set of muscles allows the upper and lower pharyngeal bones to be used as a second set of jaws for processing food, allowing a division of labor between the 'true jaws' (mandibles) and the 'pharyngeal jaws'. Cichlids are efficient and often highly specialized feeders that capture and process a very wide variety of food items. This is assumed to be one reason why they are so diverse. The features that distinguish them from the other families in Labroidei include: 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.