Ichthyology is the branch of biology that studies fishes, including their anatomy and classification.
The word comes from the Greek ikhthys, meaning “fish,” combined with -logia, meaning study. Ichthyologists examine living fish, fossils, behavior, evolution, physiology, and relationships among species. Their work covers animals as different as jawless lampreys, cartilaginous sharks and rays, and bony fishes.
The field developed alongside natural history and museum science. Early catalogues often grouped fish by visible body form, but modern ichthyology also uses genetics, anatomy, developmental biology, and evolutionary relationships. Fish diversity is enormous, with more than 35,000 living species described.
Ichthyology is narrower than marine biology, because it includes freshwater fishes as well as marine species. It is also different from cetology, which focuses on whales, dolphins, and porpoises, and malacology, which studies molluscs.