Smelt are found in estuaries and coastal waters along the Atlantic coast of Europe and northwards along the coast of Russia. Smelt are related to trout and salmon and have in common with these species a second small, fleshy dorsal fin called an adipose fin. They can be recognised by their somewhat toothy appearance and their unusual smell, which is very like cucumber.
Smelt migrate into the upper reaches of estuaries in spring to spawn in tidal freshwater sections of rivers. The young move down into estuaries after hatching, feeding on zooplankton, and adults feed on larger prey, such as shrimp and small fish. In Ireland, the conservation status of smelt was long classified as vulnerable because they were only known from the Shannon Estuary, but surveys have confirmed that there are populations found in several other estuaries of large river systems around the island.
Threats to smelt may include barriers to migration, dredging operations that affect estuaries in which they spawn, as well as water pollution and deterioration of water quality. Smelt in Ireland are also considered vulnerable to unsustainable exploitation for their use as angling dead bait.