Rainbow smelt (Osmerus mordax)

Rainbow Smelt

(Osmerus mordax)

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If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

The rainbow smelt is a small fish that is eagerly pursued by anglers because of its fine flavor. Its Latin name Osmerus, which comes from the Greek word meaning “odor”, is fitting because when removed from the water, they give off an odor which smells like freshly cut cucumbers.

Identification

The rainbow smelt has a small, slender body that typically ranges from 18-23 cm (7-9 in) long and weighs around 85 g (3 oz). Smelt are mostly silver, with pale olive-green backs and iridescent purple, blue, and pink sides. A conspicuous silvery streak runs lengthwise along each side. In the water, rainbow smelt shimmer colorfully, but when removed, they quickly fade to a silver white. In freshwater they are darker, becoming almost black on the back. The head is elongated, with a relatively large mouth and pointed snout. The lower jaw protrudes, and prominent teeth can be seen on the tongue and both jaws. Scales are thin and easily detached. A single dorsal fin and a single adipose fin lack spines. Spawning males are covered on the head, body, and fins with tiny bumps called nuptial tubercles.

Similar Species

While they may be confused with many minnow species, rainbow smelt have an adipose fin and prominent teeth that minnows lack.

Habitat

Historically, rainbow smelt have been strictly anadromous (residing in saltwater, but entering freshwater to reproduce). However, since the early 1900s the smelt has been successfully introduced into freshwater systems. It prefers deeper, cooler waters during the warmer seasons but will favor shallower coastal areas for feeding as winter approaches.

Spread

Rainbow smelt spread naturally through waterway connections. Other potential vectors include ballast water, bait bucket transfers, improper disposal of fish remains containing gametes, and intentional introduction as forage and bait fish.

Distribution

The rainbow smelt is native to the Atlantic Coastal drainages of North America and the Pacific drainages of North America and Asia. It was introduced into Michigan’s Crystal Lake as a food for stocked salmon and soon escaped into Lake Michigan. It can now be found in all of the Great Lakes, the Mississippi River, and other inland waters. In Pennsylvania, rainbow smelt populations are established in Lake Erie, the Allegheny and Monongahela river drainages, and Harvey’s Lake in Luzerne County.

 

Note: Distribution data for this species may have changed since the publication of Pennsylvania's Field Guide to Aquatic Invasive Species (Second Edition 2015), the source of information for this description.

Environmental Impacts

Rainbow smelt could impact sport fishing and native fish populations because they compete directly with sport fish such as perch, walleye, and lake trout for food. Smelt also feed on early or larval stages of other fish.

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