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 largest vertebrate families.

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.

Anatomy and appearance

The particular features of cichlids 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.
• The lateral line organ is divided 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 leaves the stomach from its left side, not from its right side as in other Labroidei.

Taxonomy

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 Cichlids, 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.