Cichlid

Cichlids are a large, diverse and widespread family of fish, Cichlidae, with at least 1,760 described species and estimates of 2,000 to 3,000, making it one of the largest vertebrate families. They are native to the Neotropics, Africa including Madagascar, the Middle East and the Indian subcontinent. Sizes run from about 2.5 cm to nearly 1 m. All share a fused lower pharyngeal bone forming a single tooth-bearing structure that works as a second set of jaws, a trait thought to underlie their diversity as feeders. Cichlids evolved rapidly into species flocks in the African Great Lakes, and all practise some parental care, either guarding eggs and fry or mouthbrooding.

About the cichlid

A cichlid is any member of Cichlidae, a family of perch-like freshwater fish with at least 1,760 described species. Cichlids are native to Africa, Madagascar, Central and South America, the Middle East, India and Sri Lanka, and their closest living relative is the marine convict blenny. Angelfish, oscars, discus and tilapia are all cichlids.

That species count makes Cichlidae one of the largest vertebrate families on Earth; only the carp family, Cyprinidae, has more species. New cichlids are still described every year, and many remain unnamed. The African cichlids are the most famous and diverse group, and they are often sorted by the lake they come from: Lake Malawi, Lake Tanganyika or Lake Victoria.

Body shape and size vary enormously. The smallest, such as females of Neolamprologus multifasciatus, are about 2.5 cm (1 in) long, while giants in the genera Boulengerochromis and Cichla approach 1 m (3 ft). Some, like the angelfish and discus, are flattened from side to side like a dinner plate. Others are long and tube-shaped. The typical cichlid, though, is a medium-sized, oval, slightly compressed fish that looks and behaves much like a North American sunfish.

The trait that unites every cichlid is hidden in the throat. The lower pharyngeal bones are fused into a single, tooth-bearing plate, and a complex set of muscles lets the upper and lower throat bones work as a second set of jaws. The front jaws capture food and the throat jaws process it. The different ways cichlids process prey with these throat jaws are believed to be one reason the family has split into so many species.

Color is the other headline feature. In the African Great Lakes, closely related species often differ most in their coloration, along with jaw shape, teeth, fins and head profile. Color can also change remarkably fast: a dominant territorial male takes on brighter, more vivid colors, while a subordinate male turns dull and pale.

Behavior and diet

Between them, cichlids eat almost everything a fish can eat. The family includes carnivores, herbivores, omnivores, plankton feeders and detritus feeders, though most individual species will take whatever food is available. Petrochromis grazes algae, while Etroplus suratensis eats plants. Trematocranus specializes in snails, and Pungu maclareni feeds on sponges.

Some feeding strategies are startling. Crenicichla species lunge at small fish from hiding, while Rhamphochromis chases prey through open water. Several genera, including Plecodus and Perissodus, bite scales and fins off other fish. Nimbochromis and Parachromis species lie motionless as if dead, then ambush small fish that come close to investigate. A few egg-eating species ram the heads of mouthbrooding females to force them to spit out their young.

Males are strongly territorial. They size up rivals by sensing water movement with the lateral line, then settle disputes with side-on displays, flared gill covers, biting and "mouth fights," head-on collisions of open mouths that measure jaw size. Females tend to choose vivid, dominant males with food-rich territories.

Parental care is universal in the family. Open brooders such as angelfish and discus lay eggs on rocks, leaves or logs, and typically the male patrols while the female fans the eggs. Cave brooders hide eggs in crevices or empty snail shells. Mouthbrooders, usually females, carry eggs or newly hatched larvae in their mouths, sometimes for several weeks. Many male mouthbrooders in the Haplochromini tribe carry "egg spots," yellow, red or orange dots on the anal fin that look like eggs. When the female tries to scoop them up, the male releases sperm and fertilizes the eggs already in her mouth.

Some parents go further. Discus and a few other cichlids feed their fry a mucus secreted from their skin. In the daffodil cichlid, closely related males from neighboring territories help rear the breeding male's young.

Range and habitat

Cichlids are most diverse in Africa and South America. Africa alone holds an estimated 1,600 or more species, and Central America and Mexico have about 120, reaching as far north as the Rio Grande in South Texas. Madagascar has its own distinct lineages. In Asia, native cichlids are limited to about nine species in Israel, Lebanon and Syria, two in Iran, and three in India and Sri Lanka. Europe, Australia and North America north of the Rio Grande have no native cichlids, although feral populations are established in Florida, Hawaii and elsewhere.

Most species live in fairly shallow fresh water, but there are exceptions. Trematocara has been found more than 300 m (1,000 ft) down in Lake Tanganyika. The Mayan cichlid is equally at home in freshwater marshes and mangrove swamps, and members of Alcolapia and Danakilia live in hot, salty lakes. One Eritrean lake, home to Danakilia dinicolai, ranges from 29 to 45 °C (84 to 113 °F).

The three African Great Lakes are the family's evolutionary showcase. Repeated rises and falls in lake level split fish populations apart and then reconnected them, and the cichlids of Lake Victoria diversified within roughly the last 10,000 to 15,000 years.

Cichlid vs tilapia

Tilapia are not a separate kind of fish; they are cichlids. The name covers several genera of fast-growing species that are farmed worldwide for food.

Conservation status

Cichlids as a family have no single IUCN status, because each species is assessed separately. They do, however, have more threatened species than any other vertebrate family. In 2010 the IUCN Red List classed 184 cichlid species as vulnerable, 52 as endangered and 106 as critically endangered. One, Yssichromis sp. nov. argens, is listed as extinct in the wild, and six are fully extinct.

Lake Victoria shows how quickly a cichlid fauna can collapse. The introduced Nile perch and Nile tilapia, water hyacinth, silt from deforestation and overfishing wiped out at least 200 of the lake's 500-plus haplochromine species, about 40 percent. Cichlids once made up about 80 percent of the lake's fishery catch; by around 1980 they were just 1 percent. Some species have reappeared since the Nile perch declined in the 1990s, surviving in satellite lakes or among rocks and papyrus.

Cichlids can also become the problem. Many introduced outside their range have turned into nuisances, and flowerhorn hybrids released in Malaysia and Singapore threaten local fish communities.