Order (Taxonomy)

Orders in fish taxonomy group families sharing a common phylogenetic origin and a suite of derived characters (synapomorphies). Historically, Perciformes was a taxonomic wastebasket for perch-like fish — any spiny-finned fish not fitting elsewhere was placed there. Modern molecular analyses have dismembered it into dozens of new orders. Siluriformes (catfish, ~3,700 species), Cypriniformes (carp and relatives, ~3,500 species), and Characiformes (tetras and relatives, ~1,500 species) dominate freshwater systems globally. Taxonomic revisions at the order level directly affect conservation listings and regulatory frameworks that reference taxonomic names.