Cichlid

Cichlids are a large and varied family of percomorph fish, officially placed in the family Cichlidae under the order Cichliformes. At least 1,760 species have been formally described, making this one of the biggest vertebrate families—only the Cyprinidae contains more known species. New species are found every year, and many have not yet been described, so the true total is unknown, with estimates ranging from 2,000 to 3,000. These fish are originally from the Neotropics, Africa (including Madagascar), the Middle East, and the Indian subcontinent, though people have introduced some species to waters around the world.

Many cichlids, especially tilapia, are raised as food fish, while others, like those in the genus *Cichla*, are popular game fish. The family also includes well-known freshwater aquarium species such as angelfish, oscars, and discus. Among vertebrate families, cichlids have the highest number of endangered species, most of which belong to the haplochromine group. They are famous for evolving rapidly into many different forms—known as species flocks—in the African Great Lakes. Key differences among these forms include jaw and tooth structure, fin, head, and body shape, and especially coloration. This diversity makes them important for studying how new species arise. When introduced outside their natural range, many cichlids become nuisance species.

All cichlids care for their eggs and young in some way, typically by guarding them or by mouthbrooding.

The fast speciation in Lakes Victoria, Malawi, and Tanganyika is partly due to their geological and climate history. Tectonic rifting about 20–25 million years ago created the rift system and eventually formed the basins of these three lakes. Lake Tanganyika, the oldest, formed roughly 12–9 million years ago, while Lake Malawi deepened later, during the Pliocene (around 5–2 million years ago). Sediment cores from Lake Malawi show that over the past 1.3 million years, the lake level dropped at least 24 times by 200 meters and 14 times by 400 meters; similar patterns occurred in the other two lakes. These lowstands reduced available habitats and isolated fish populations, while highstands refilled the lakes, increased habitat, and reconnected populations, allowing hybridization and gene flow.

Cichlids vary greatly in size, from species as small as 2.5 cm (1 in) long, such as female *Neolamprologus multifasciatus*, to much larger ones approaching 1 m (3 ft), like *Boulengerochromis* and *Cichla*. Their body shapes also range widely, from strongly compressed forms (e.g., *Altolamprologus*, *Pterophyllum*, and *Symphysodon*) to cylindrical, elongated ones (e.g., *Julidochromis*, *Teleogramma*, *Teleocichla*, *Crenicichla*, and *Gobiocichla*). In general, though, cichlids tend to be medium-sized, oval, and slightly compressed, similar to North American sunfishes in shape, behavior, and ecology.

A key trait shared by all cichlids is the fusion of the lower pharyngeal bones into a single tooth-bearing structure. A complex set of muscles lets these bones work as a second set of jaws for processing food, splitting the work between the true jaws and the pharyngeal jaws. This makes cichlids efficient and often highly specialized feeders that handle a wide variety of food, which is thought to be one reason for their diversity.

The current consensus taxonomy, based on the Catalog of Fishes (2025), places cichlids into four subfamilies: Etroplinae (Indian and Madagascan cichlids), Ptychochrominae (Malagasy cichlids), Pseudocrenilabrinae (African cichlids), and Cichlinae (American cichlids). In the past, classifications varied; Kullander (1998) recognized eight subfamilies, and Sparks and Smith later added a ninth. Cichlid taxonomy is still debated, with no complete agreement on genera or a system that assigns all species to monophyletic groups. For example, Kullander placed the African genus *Heterochromis* within Neotropical cichlids, though later studies disagreed. Other issues involve the common ancestor of the Lake Victoria superflock and the ancestral lineages of Lake Tanganyikan cichlids. Phylogenies based on morphology sometimes differ from those based on genetics, but there is consensus that the family Cichlidae is monophyletic. Dentition was once used for classification, but tooth shapes change with age and wear, making it unreliable. Genome sequencing and other technologies have since transformed cichlid taxonomy. Alternatively, all New World cichlids can be placed under Cichlinae, while Etroplinae covers all Old World species.

The external taxonomic placement of cichlids was long disputed and variable, but has now been largely resolved. In the past, based on morphology, they were classified in a different group.