Rainbow smelt

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Rainbow smelt

Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Osmeriformes
Family:	Osmeridae
Genus:	Osmerus
Species:	O. mordax

Binomial name

Osmerus mordax
(Mitchill, 1814)

Subspecies

Osmerus mordax mordax
Osmerus mordax dentex

Rainbow Smelt (Osmerus mordax) is an anadromous species of fish inhabiting rivers and coastal areas of North America from New Jersey to Labrador on the east coast and from Vancouver Island to the Arctic Ocean on the west coast. It has been introduced to the Great Lakes and from there has made its way to various other inland bodies of water in Ontario and the midwestern United States.

The body of the rainbow smelt is slender and cylindrical. It has a silvery pale green back and is iridescent purple, blue, and pink on the sides, with a light underside. When fullgrown, the rainbow smelt is between seven and nine inches long and weighs about three ounces, and ones over 12 inches are known. They eat zooplankton, invertebrates and other fish, including small smelt, sculpins, burbot, and whitefish. They are preyed upon by larger predatory fish such as coho salmon, burbot, trout, walleye, and yellow perch.

Rainbow smelt are fished both commercially and for sport. Commercial harvests are down from historic levels; for example around 1850 an annual harvest from the Charles River alone was around 9 million fish. They are commonly processed into animal feed, but are also eaten by humans. They are a popular winter game fish and the spring smelt run is a tradition in many parts of their distribution. Since being introduced to the Great Lakes, rainbow smelt have been considered an invasive species and though they provide food for many native species of larger game fish, they also prey upon the young of these and other fish. They have been found to impact populations of lake herring, yellow perch, whitefish, bloaters, alewives, slimy sculpin, walleye, and lake trout.

In their anadromonous territories, they spend the summers along the coast, normally in waters no more than 20 feet deep and no more than a mile from shore. They overwinter under the ice in estuaries, producing an anti-freeze protein containing glycerol. In the spring, they spawn at night in small streams, often ones that go dry in the summer. Landlocked populations were historically known in Maine, and it was from one of these that they were introduced to one of the lakes in Michigan known as Crystal Lake, and then spread to the Great Lakes.