Osmeriformes

Osmeriformes is an order of ray-finned fishes (Actinopterygii) that includes several lineages commonly referred to as smelts and their relatives. In many classifications, the order is placed within the clade Protacanthopterygii and comprises species that inhabit marine, estuarine, and freshwater environments. The best-known group is the family Osmeridae, the smelts, which typically have slender, laterally compressed bodies and are found in temperate regions. Many smelts are migratory, spawning in freshwater or brackish habitats after spending part of their lives at sea.

Other groups that have historically been included in Osmeriformes or in closely related lineages include the southern hemisphere Retropinnidae (whitebait) and, in some schemes, the galaxiids (Galaxiidae). Modern classifications vary, and some authorities place galaxiids in a separate order, Galaxiiformes, or treat them in a broader Osmeriform assemblage. Because of differing taxonomic treatments, the exact composition of Osmeriformes has changed over time.

Ecology and life history: Osmeriformes species occupy a range of habitats from coastal waters to rivers and lakes. Many species exhibit anadromous or catadromous life cycles, migrating between the sea and freshwater to reproduce. Diet generally consists of zooplankton, crustaceans, and small fishes, depending on life stage and availability.

Fossil record: Osmeriforms have a fossil record extending back to the Cretaceous in some lineages, providing insight into the early diversification of protacanthopterygian fishes.