Cichlids (family: Cichlidae) are a group of freshwater fish species, medicine typically encountered in South America, Africa, India and Madagascar. The family so far consists of more than 1500 species with the list increasing as more species are described every year. They are typically encountered in lakes and rivers, however some species have been reported in saltwater, mainly in brackish waters and coastal areas.
Members of the group can be distinguished by a number of discrete characteristics: a single nostril on each side of the head instead of two, the absence of bony shelf below the eye and the separation of the lateral line* in two sections. Another very important characteristic of cichlids is their “pharyngeal jaws”, a second pair of jaws which derive from a transformation of their gills. This tool complements the mouth structure, helping to crash and process food items such as invertebrates. It has also allowed some cichlids to specialize in specific preys, leading to a great diversity of species within the family.
Cichlids display strong sexual dimorphism, i.e. females and males can be easily distinguished by special characteristics. Female and male individuals differ in color and size: males are typically bigger and more colorful than females. It is due to this great diversity of colors that cichlids are considered some the most famous ornamental fish among aquarists. Another interesting characteristic of cichlid species is their reproductive behavior. Males and females usually engage in a stunning reproductive process including mating, spawning, fertilizing and guarding the eggs. Moreover, in most species the female collects the eggs and keeps them in its mouth, a procedure that is known as oral incubation.
Cichlid species are known for their incredible diversity, which is due to their fascinating evolution. They are considered secondary freshwater species, because their ancestors were seawater species that made their way to the freshwater environment. As a result, cichlids are extremely tolerant to high salinities, which provided them a great advantage in waters rich in salts and minerals. The first cichlid species probably appeared in Africa some million years ago, in waters that were saturated with salts. During that time most of the continents we know today were forming a single continent called “Pangea”. Later on the several continents drifted apart and so did the several cichlid species, resulting in the distribution that they have today.
It is due to their evolution that cichlids are usually classified in two groups: the new world species and the African cichlids. The first group includes South American cichlids, cichlids from India and Madagascar, thus cichlids from continents that drifted further apart from Africa, which is considered the “old world”. Although this hypothesis seemed to explain the distribution and evolution of cichlids, recent studies in the genetic biology of certain cichlid species presented evidence that it might not be the case. Alternatively, they suggested that some species might have crossed entire oceans, a long migration that through the years allowed the evolution of such a rich diversity of cichlids in lakes and rivers of Africa, South America and Madagascar.
*Lateral line: A group of special skin cells that help fish to detect motion and orientate, and create a visible line that crosses the body of the fish almost from head to tail.
Stratton R.F. 2002. The Guide to Owning Cichlids, T.F.H. Publications, Inc.