The deep-sea smelts are any members of the family Bathylagidae, a distinct group of marine smelts.
Deep-sea smelts are marine fishes found in deep waters throughout the oceans, down to 1500m (4,900feet) in depth. They are small fishes, growing up to 25cm (10inches) long. They feed on plankton, especially krill.
Extinct genera known only from fossil remains include Quaesita from California, USA and Krumvirichthys from the Czech Republic. The oldest fossils are otoliths from the Maastrichtian.[1]