The Pacific rainbow smelt (Osmerus dentex), also known as the Arctic rainbow smelt or cucumber fish in Japan,[citation needed] is a North Pacific species of fish of the family Osmeridae.

The fish usually lives in marine and brackish environment, with a wide distribution from North Korea, Sea of Okhotsk to Bering Sea and British Columbia.

[2] They are also seen in estuaries and coastal waters of European and Siberian shores of Arctic Ocean from White Sea to Chukota in Russian Far East.

[3] The Pacific rainbow smelt has a cylindrical elongated body shape, with lengths ranging between 14 and 16 centimetres (5.5 and 6.3 in).

[3] Pacific rainbow smelt usually return to their natal streams to spawn when the water temperature reaches 2 degree Celsius and above, but the degree of homing varies from one population to another and may be genetically controlled.