Actinopterygians, also known as ray-finned fishes, are a diverse group of bony fish characterized by their fin structure, which is supported by bony rays. They are the largest class of vertebrates, with over 30,000 species, including familiar types like salmon, trout, and goldfish. Actinopterygians inhabit a wide range of environments, from freshwater rivers to the deep sea. These fish have a streamlined body and a swim bladder that helps them maintain buoyancy. Their gills allow for efficient respiration in water, and they possess scales that provide protection. Actinopterygians play essential roles in aquatic ecosystems and are significant for human activities, including fishing and aquaculture.