Cichlid

Cichlids are a massive and incredibly diverse family of fish.

They belong to the family Cichlidae within the order Cichliformes. Scientists have formally described at least 1,760 different species. However, many more species likely exist but have not been named yet. Estimates suggest the true number could be between 2,000 and 3,000 species. This makes them one of the largest vertebrate families on Earth. Only the Cyprinidae family has more species.

These fish are found in the Neotropics, Africa, the Middle East, and the Indian subcontinent. While most live in freshwater, some have been introduced to waters all over the world.

One of the most fascinating things about cichlids is their unique anatomy. All cichlids share a specific trait: the fusion of their lower pharyngeal bones. These bones form a single, tooth-bearing structure located near the throat. A complex system of muscles allows these bones to act as a second set of jaws. This creates a division of labor between the mandibles, which are the true jaws, and the pharyngeal jaws.

Because they have two sets of jaws, they are highly efficient feeders. They can capture and process a huge variety of different food items. This specialized feeding ability is likely a major reason why they have become so diverse.

Cichlids also show a massive range of physical appearances. They vary greatly in body size. Some species, like the female Neolamprologus multifasciatus, are very small. Other species, such as Boulengerochromis or Cichla, can grow much larger. Their body shapes are just as varied. Some species are laterally compressed, meaning they are flattened from side to side. Examples include the Altolamprologus and the colorful Discus.

Other cichlids are cylindrical and elongated, like the genus Julidochromis. Most cichlids, however, tend to be medium-sized and ovate in shape.

Parental care is a defining behavior for this family. Every cichlid species practices some form of care for their eggs and fry. Fry are the young fish that have just hatched. Some species guard their eggs and young on the ground or on a surface.

Other species use a method called mouthbrooding. In mouthbrooding, the parent carries the eggs or the fry inside their mouth for protection.

This dedicated care helps ensure that more offspring survive to adulthood.

In the African Great Lakes, cichlids undergo rapid evolution. This process is called speciation, where new species form quickly. This happens in Lakes Victoria, Malawi, and Tanganyika. The history of these lakes is tied to tectonic rifting. This geological activity occurred about 20 to 25 million years ago. It created the basins that hold these massive lakes. Lake Tanganyika is the oldest, forming between 12 and 9 million years ago. Lake Malawi formed more recently during the Pliocene, about 5 to 2 million years ago.

Climate changes in these lakes drove the evolution of the fish. Sediment cores show that lake levels fluctuated wildly over time. In Lake Malawi, there were at least 24 drops in water level of 200 meters. There were also 14 drops of 400 meters. These drops were caused by dry periods and changes in precipitation. When water levels dropped, fish populations became geographically isolated. This isolation allowed them to evolve into different species. When water levels rose again, the populations reconnected. This allowed for hybridization and gene flow between the groups.

Scientists have long debated how cichlids spread across the globe. Some believed they moved when the supercontinent Gondwana broke apart. This would mean cichlids are an ancient group from the Early Cretaceous. However, new studies using molecular phylogenetics tell a different story. DNA evidence suggests cichlids are much younger than the breakup of Gondwana. They likely originated during the Late Cretaceous or the Eocene. This means they must have dispersed across oceans to reach different continents. How freshwater fish crossed thousands of kilometers of salt water remains a mystery. They may have used narrow oceans or large river plumes to travel.

Today, cichlids are very important to humans in many ways. Many species, like tilapia, are vital food sources. Others, like the Cichla species, are prized as game fish. They are also among the most popular fish for aquarium hobbyists. People love keeping species like angelfish, oscars, and discus in home tanks.

However, the family also faces serious challenges. Cichlids have the largest number of endangered species among vertebrate families. Most of these endangered species belong to the haplochromine group. Protecting their natural habitats is essential for their survival.