Characiformes

Characiformes is a massive order of ray-finned fish. It includes the characins and many of their close relatives. This group is incredibly diverse, containing over 2,000 different species. You might recognize some of them, like the famous piranha or various types of tetras.

These fish play vital roles in the ecosystems where they live. They are found in many different freshwater environments around the world.

Most characins live in the Neotropics. This region includes the rivers and lakes of South and Central America. However, they are not only found in the Americas. At least 209 species live in Africa. These African species include groups like the distichodontids, citharinids, alestids, and hepsetids.

The vast majority of characins, however, are native to the Americas.

Characins have unique physical features that help them survive. One special feature is the Weberian apparatus. This is a series of bony parts inside the body. These bones connect the swim bladder to the inner ear.

This connection likely helps them sense sounds. Most characins also have teeth because they are often carnivorous. Their bodies are usually covered in well-defined scales. Some species even have a small, fleshy adipose fin. This fin is located between the dorsal fin and the tail.

Scientists categorize these fish into many different groups. The Characiformes belong to a larger group called the Otophysi. The Otophysi also include the orders Cypriniformes, Siluriformes, and Gymnotiformes. Within the Characiformes, there are 18 recognized families and about 270 genera.

Originally, scientists placed all characins into just one family called Characidae. Modern research has since separated them into many distinct families. A 2011 study helped confirm that the Characidae family is monophyletic, meaning they share a common ancestor.

The sizes of characins vary wildly. Some species are very large and are important for food or game. The goliath tigerfish, known as Hydrocynus goliath, is one of the largest.

Other large examples include the golden dourado and the wolffish. In contrast, many characins are very small. The smallest is the Bolivian pygmy blue characin, which is only about 10 millimeters long. Many small species are called forage fish because they swim in large groups called shoals. Many tetras are popular in home aquaria because of their bright colors and hardiness.

The history of these fish is tied to the movement of continents. Characiforms likely originated on the supercontinent of West Gondwana. This landmass later split into Africa and South America.

This geological split explains why they are found on both continents today. During the Cretaceous period, the Atlantic Ocean was forming between these lands. Fossil evidence shows that characins once lived much further north than they do today. This includes fossils found in places like Hungary, Morocco, and North America. Scientists believe the warmer climate of the Late Cretaceous allowed them to live in these northern regions.

Understanding Characiformes helps us learn about evolution and Earth's history. Their distribution reflects how landmasses have shifted over millions of years. By studying their fossils and their DNA, researchers can trace how life changes. The way they interact with other fish also shows how ecosystems work. From tiny tetras to massive tigerfish, they are a key part of the world's freshwater life.