Teleosts are a diverse group of ray-finned fish that represent the most advanced and abundant class of vertebrates, known for their outstanding adaptability and successful colonization of various aquatic habitats. They belong to the superclass Actinopterygii, which includes more than 30,000 species and makes up approximately 96% of all fish species. Teleosts exhibit a wide range of sizes, shapes, colors, and ecological roles, and can be found in almost every aquatic environment, from freshwater to marine, tropical to polar regions.
These fish are characterized by their bony skeleton, with true bone replacing cartilage as the main structural material. They possess a swim bladder, an air-filled sac located in the abdominal cavity, which helps control buoyancy and facilitates forward movement. Additionally, teleosts have a homocercal tail fin, with the upper and lower lobes of the tail being roughly symmetrical. This tail shape allows for efficient propulsion through the water.
Teleosts also typically possess scales that are either cycloid, with smooth edges, or ctenoid, with comb-like edges. Cycloid scales are generally found in more primitive species, while ctenoid scales are more common in advanced teleosts. The presence of these scales plays a role in minimizing water drag and protecting the fish from injuries and infections.
These fish are characterized by an advanced reproductive system, with internal fertilization common in many species. Most teleosts are oviparous, laying eggs that are externally fertilized, although some species exhibit various other modes of reproduction.
Teleosts are important ecologically, commercially, and in scientific research, serving as valuable food sources, recreation for fishing enthusiasts, and as model organisms for studying evolution, physiology, and behavior.
