Fish
Cichlid
Cichlidae · also called cichlids
Cichlids are the fish that evolution seems to make in bulk. In a single African lake, one ancestor can turn into five hundred species — different colours, different jaws, different diets — in the time since the last ice age. The family also raises its young more carefully than almost any other fish, many of them carrying eggs and fry around in the parent’s mouth.
Overview
Cichlids are the family Cichlidae, well over 1,700 species and probably more than 2,000, one of the largest of all vertebrate families. They are freshwater fish of Africa, the Americas, Madagascar, and southern Asia, most diverse by far in the East African Great Lakes. Diet across the family runs the full range — algae scrapers, snail crushers, plankton filterers, fish hunters, even scale biters.
Made for radiation
Lake Victoria’s ~500 endemic cichlids arose in perhaps 15,000 years; Malawi and Tanganyika hold hundreds more. These are the fastest known adaptive radiations of vertebrates. A big reason is a second set of jaws in the throat, the pharyngeal jaws, which process food and free the outer jaws to specialise fast.
Devoted parents
Nearly all cichlids guard a territory, tend the eggs, and shepherd the fry. Many African species are mouthbrooders — the female holds the eggs and young in her mouth for weeks, not feeding, and lets the fry shelter back inside when danger comes.
Feeding people, and a warning
The tilapias, chiefly the Nile tilapia, are among the world’s most farmed fish. But the wild cichlids of Lake Victoria suffered one of the largest vertebrate extinction events on record from the 1980s, when the introduced Nile perch, pollution, and overfishing wiped out or crashed 200 to 300 endemic species.
Status
Cichlids as a family are Not Evaluated, trend decreasing. Farmed tilapias are abundant, but the Great Lakes faunas are among the most threatened vertebrate groups, and many narrow-range river and crater-lake cichlids in Africa, Madagascar, and Central America are endangered.
Cichlid: common questions
Why are cichlids so important to the study of evolution?
Because they show how new species form, faster and more visibly than almost any other group of animals. In the African Great Lakes, single ancestral cichlids have given rise to hundreds of distinct species each, differing in colour, jaw shape, diet, and behaviour, over timescales as short as a few thousand to a few tens of thousands of years. This lets biologists watch adaptive radiation unfold, test which factors drive it, such as female colour preference, ecological opportunity, and the flexible pharyngeal jaws, and compare independent radiations in different lakes that have often converged on similar body types. Cichlids are to the study of speciation roughly what fruit flies are to genetics.
What is mouthbrooding?
Mouthbrooding is a form of parental care in which a parent fish carries the eggs, and usually the newly hatched young, inside its mouth. In the maternal mouthbrooding common in African cichlids, the female picks up the eggs immediately after they are laid and fertilised, holds them in a pouch in the floor of the mouth through incubation and the yolk-sac stage, and does not eat during this period, which can last one to four weeks. Once the fry can swim and feed they are released, but for several more days they dart back into the mother's mouth when she signals danger. It protects the young from the intense predation in these lakes at the cost of the parent's feeding and condition.
Are the cichlids sold in aquarium shops the same as wild ones?
Often they are only a few generations removed from the wild, and some are wild-caught. The aquarium hobby has driven collection of African and South American cichlids for decades, and while many popular species are now captive-bred, and some, such as the blood parrot and flowerhorn, are artificial hybrids that do not exist in nature, others are still taken from lakes and rivers. This trade has both harmed some wild populations and, in a few cases, maintained species in captivity that have become rare or extinct in the wild. Released aquarium cichlids have also established wild populations in warm waters such as Florida.
What happened to the cichlids of Lake Victoria?
Lake Victoria once held around 500 species of cichlid found nowhere else, one of the richest concentrations of vertebrate life on Earth, most of which had evolved within the last 15,000 years. From the 1980s a large fraction of them, perhaps 200 to 300 species, disappeared or crashed. The main causes were the Nile perch, a large predator introduced decades earlier that boomed and ate its way through the smaller cichlids, together with nutrient pollution from farming and sewage that clouded the water and removed the visual cues females use to choose mates of their own species, causing some to hybridise and merge. It stands as one of the largest and fastest vertebrate extinction events in recorded history.