Rainbow Smelt (Osmerus mordax)

One of the most prominent members of the Osmeridae family of smelt, the rainbow smelt is an important forage species for predatory fish and a principal target for inland and coastal commercial fishing.

It is a close relative of the eulachon of the Pacific, the pond smelt (Hypomesus olidus) of the western Arctic, the capelin of the Atlantic, and the European smelt (Osmerus eperlanus).

Other Names

American smelt, frostfish, leefish, toothed smelt, freshwater smelt; French: éperlan du nord.

Identification

The rainbow smelt is a slender, silver fish, with a pale green or olive-green back. Fresh from the water, the sides of the fish take on a purple, blue, or pink iridescent hue. The scales on the rainbow smelt are large and easily detached, and at spawning time those on the males develop small tubercles, resembling tiny buttons that serve as a mark of their sex.

The lower jaw of the fish projects beyond the upper one, and the entire mouth extends beyond the middle of each eye. On the tip of the tongue are large teeth. One large dorsal fin is located about halfway along the back, and behind that is a small adipose fin.

Size/Age

Most rainbow smelt are less than 8 inches long, although some coastal specimens have measured 14 inches. They may live for at least 6 years.

Spawning behavior

In the spring, anadromous adult rainbow smelt migrate upstream to freshwater spawning grounds. Spawners reach the tide head in the main tributaries when the water temperature is only 39° to 41°F. Spawning occurs at night, typically over a gravelly bottom.

Rainbow smelt remain at spawning sites for a number of days before migrating downstream. Shortly after spawning, many males die. Some rainbow smelt are mature at 2 years of age, and all are mature at age 3.

Food

Zooplankton, insect larvae, aquatic worms, and small fish constitute the diet of rainbow smelt, with zooplankton being predominant.

Distribution

The rainbow smelt is widely distributed throughout eastern and western North America, inhabiting coastal waters, as well as countless inland freshwater lakes. On the Atlantic coast it ranges from New Jersey in the south to Hamilton Inlet, Labrador, in the north. Populations of rainbow smelt also exist on the Pacific coast from Vancouver Island northward around Alaska and eastward along the Arctic coast at least as far as the Mackenzie River.

Habitat

The rainbow smelt is a pelagic schooling species, inhabiting inshore coastal regions and the midwaters of lakes. Because it is sensitive to both light and warmer temperatures, schools of rainbow smelt tend to concentrate near the bottoms of lakes and coastal waters during daylight hours.