|Family overview: The smelts are coldwater fishes that live throughout the Northern Hemisphere. Smelt are anadromous fish. They spawn in fresh water and live in the ocean as adults. They can also live entirely in fresh water.
Only one species of smelt is found in Pennsylvania–the rainbow smelt (Osmerus mordax). Rainbow smelt were originally found in the North Atlantic and North Pacific oceans. They were introduced into Lake Michigan in 1912, and in the following years spread throughout the Great Lakes. Rainbow smelt are in Pennsylvania in Lake Erie and Presque Isle Bay, where they are an important food for large, predatory fish. They were also introduced into Harvey’s Lake, Luzerne County, in 1952, as well as large impoundments like Raystown Lake and the Allegheny Reservoir, as forage for larger predatory fish. Rainbow smelt are occasionally observed in the Delaware River in Pennsylvania. The Delaware is the extreme southern end of their range.
The genus name “Osmerus” means “smell” or “scent,” in reference to the “sliced cucumber” odor that is noticeable in breeding adults. The species name “mordax” means “biting.”
Identification: The rainbow smelt is a small, slender, silvery fish, with a comparatively large mouth and strong teeth. Its large scales are cycloid, or smooth, and the upper jaw extends beyond the eye. The rainbow smelt’s color is rainbowlike, ranging from pale to dark-olive on the back, to purple and pink on the sides, and shading to dark-blue and violet near the belly, which is whitish. The tail is deeply forked. Like trout, salmon and catfish, the smelt has a fleshy adipose fin, a small fin lobe on the back between the dorsal and caudal fins. Spawning males develop very fine, sharp projections, called tubercles, on the head and body. Rainbow smelt grow to seven or eight inches long.
Life history: Rainbow smelt spawn early in the spring, when the water is in the mid-40s to upper 40s. Smelt run upstream into the mouths of small creeks to spawn at night, or they deposit their eggs along the lake shore. Each female releases 10,000 to 30,000 tiny, sticky eggs, which adhere to clean bottom sand or gravel. Two or more males accompany a female during spawning, and the breeding season lasts about a week. Eggs hatch in two to three weeks, and young smelt grow to about three inches their first year. Smelt are mature and ready to spawn in two or three years. They live five or six years. Young smelt live in the lake shallows in the summer, but move to deeper water in autumn. Adult smelt congregate in huge midwater schools in Lake Erie, but move closer to the surface at night.
Young smelt eat tiny aquatic organisms, but switch to aquatic insect larvae and other invertebrates and small fish as they grow. They may turn the table on their predators, and feast on the predator fish’s young. Anglers “dip” smelt with nets during the spawning run. Anglers also fish for them with tiny baited hooks and jigs through the ice. In some places, smelt are important commercially, but not in Pennsylvania.