Salmoniformes

Salmoniformes is an order of ray-finned fishes (Actinopterygii) that includes several cold-water lineages known for their anadromous life histories and economic importance. The group’s composition has varied among taxonomic schemes; the family Salmonidae (salmon, trout, and chars) is consistently included, while the placement of smelts (Osmeridae) and related groups differs between classifications, with some systems treating these taxa as a separate order (Osmeriformes). In practice, much of the time Salmoniformes is discussed as encompassing the Salmonidae and, in some accounts, the Osmeridae.

Members of Salmoniformes are typically elongated and streamlined, with a fusiform body shape adapted to both freshwater and marine habitats. A distinguishing feature in many species is the presence of an adipose fin, and they generally possess a well-developed lateral line and a forked caudal fin. Reproduction involves demersal eggs laid in gravel in freshwater streams; many salmonids exhibit anadromous life cycles, migrating to the sea to grow before returning to freshwater to spawn, though numerous freshwater resident forms also exist.

Geographic distribution is largely Northern Hemisphere, with species native to North America, Europe, and Asia. Ecologically, salmoniform fishes occupy a range of freshwater and marine environments and are often top or mid-level predators, feeding on invertebrates and smaller fishes. They are of substantial economic importance due to commercial fisheries and aquaculture; Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) are prominent examples in aquaculture.

Taxonomically, Salmonidae is the most diverse family within Salmoniformes, including subfamilies such as Salmoninae (true salmon and trout) and Coregoninae (whitefishes and Cisco). The precise circumscription of Salmoniformes and its families varies by authority, reflecting ongoing revisions in fish phylogeny.