Rainbow Smelt: 21 Facts You Won’t Believe!

Rainbow smelt facts like it is a tiny but long fish are interesting.

Rainbow smelt (Osmerus mordax) is a small shallow water fish that is usually found in lakes, streams and coastal regions of Canada and North America near the North Atlantic regions. This fish is a small looking fish that grows between 5.9-9.8 in (15-25 cm) in length. To identify a rainbow smelt, you need to look for a fish that has an arrow like pointy head that holds a large mouth with teeth in it and an adipose fin on its body. When caught fresh, it shines iridescently and gives off a cucumber like smell.

To find a rainbow smelt, one has to find themselves across North American watersheds. The native range of this particular fish is found through the Atlantic basins. It has been introduced in the lakes and several other water bodies of US regions. It is found even in the Pacific drainages, that is, rivers as far south as Vancouver Island. It is safe to assume that it is found in both fresh and saltwater bodies of the North American continent. In terms of fishing, rainbow smelt is fished both commercially and for sport in streams and seas.

You will find in this article information like rainbow smelt's habitat, rainbow smelt's predators, rainbow smelt population, rainbow smelt migration, and so on.

You may also check out our fact files on the smelt and delta smelt from Kidadl.

Rainbow Smelt

Fact File

What do they prey on?

Zooplankton, small ciscoes, and other small organisms

What do they eat?


Average litter size?

8,000-69,000 eggs

How much do they weigh?

0.0625-0.375 lb (30-170 g)

How long are they?

6-10 in (15-25 cm)

How tall are they?


What do they look like?

Olive green on the back, with purple, pink, and blue iridescence on the sides and a silvery belly

Skin Type

Wet and slimy scales

What are their main threats?

Invasive species, fluctuations in water level in spawning streams, and humans

What is their conservation status?

Least Concern

Where you'll find them

Rivers, coastal areas, and ponds


Coastal regions of North America and lakes in the Ottawa Valley in the St. Lawrence River watershed




Ray-finned fishes

Scientific Name

Osmerus mordax





Rainbow Smelt Interesting Facts

What type of animal is a rainbow smelt?

The rainbow smelt, Osmerus mordax, is a type of fish that belongs to the family of Osmiridae. Since its introduction in the Great Lakes, it has spread to various parts of the North American Continent. It is not a native species.

What class of animal does a rainbow smelt belong to?

Rainbow smelt is a fish that belongs to the Animalia Kingdom, Actinopterygii class.

How many rainbow smelt are there in the world?

Rainbow smelt, Osmerus mordax, is considered under the Least Concern status after a number of efforts were put in to reduce the human impact. Their populations drastically decreased after facing erosion and dams on rivers in the '80s but after conservation efforts, the species was moved from Endangered to its current status. As of today, it is widely fished commercially and for sport.

Where does a rainbow smelt live?

North American watersheds are home to the rainbow smelts population. They are present in abundance across the Atlantic to the Arctic Drainages and the Pacific Drainages. Post its introduction to the US states, it has now spread to the Great Lake as well. With its emergence in Lake Ontario, it was theorized that it dispersed to said lake and many other Great Lakes via natural waterways from Fingers Lake, New York. Rainbow smelt is found in rivers, coastal areas, seas, streams, and ponds.

What is a rainbow smelt's habitat?

Adult rainbow smelt spawns in freshwater at night from fish eggs which require a steady fast stream of water and an abundance of aquatic vegetation for the best chances of survival. Populations spend most  summers along the coast in anadromous territories. During the harsh North American winters, it survives under the ice sea habitat by producing glycerol and an antifreeze protein. They move from saltwater of a sea to freshwater to spawn. This fish is capable of spending its whole life in fresh water after spawning in a landlocked water body.

Who do rainbow smelts live with?

The rainbow smelt is usually found in the mid water column and seen traveling in schools.

How long does a rainbow smelt live?

It has a life expectancy of up to seven to eight years.

How do they reproduce?

Rainbow smelt's nature is to return to rivers, freshwater lakes, streams, and waterbodies after reaching sexual maturity to spawn. Sexual maturity depends on the distribution of food abundance and water temperature. Smelt rainbow reaches sexual maturity to spawn in two to six years. Once in the freshwater region, the females will extrude eggs with adhesive so that they attach themselves to substrates like mud, submerged vegetation, or gravel. After the spawning, the fish eggs hatch in one to four weeks.

What is their conservation status?

For their use as fertilizer, cattle feed, and fisheries, the rainbow smelt was fished at sea in the 1800s. Access to the spawning area has significantly decreased due to dams and culverts. An increase in the nutrient load in water due to overuse of fertilizer in crops and its runoff has raised concerns for the survival of the eggs with the growth of algae. Smelt rainbow was moved to the status of Least Concern.

Rainbow Smelt Fun Facts

What do rainbow smelts look like?

A rainbow smelt has a small, slender, cylindrical, and purple and blue body. It has a silvery finish to it and a fresh rainbow smelt shows iridescence of purple, blue, and pink on the sides. The back of the fish looks pale green and fashions a light underside with an adipose fin. With a pointy head and a large mouth with teeth.

A rainbow smelt is a small fish which fashions an iridescent shade

How cute are they?

Rainbow smelt does not particularly invoke the idea of something being cute when looked at even with their teeth.

How do they communicate?

These sea fish communicate with each other via gestures of fins and motions in various schools of fish. With that said, there has been no specific scientific study that has pinpointed how they communicate with their own kind.

How big is a rainbow smelt?

An average rainbow smelt with its fin is around 6-9 in (15.2-22.8) in length. This makes it an ideal catch to store or to cook easily. In comparison, it measures to be half as tall as a bowling pin. It isn’t particularly a game fish and yet, it's a part of various traditional winter fishing cultures in its distribution. Maybe things would look a little different in fisheries.

How fast can a rainbow smelt swim?

Not much is known about a rainbow smelt's swimming speed. Since the birth of spawn, they are not known to be fast swimmers and are usually considered to be weak swimmers. With their bony and long body and lack of muscles on it, these fish do not stray too far from the coastline at sea. They often swim not more than 20 ft (6 m) deep under the surface.

How much does a rainbow smelt weigh?

An average adult Rainbow Smelt would weigh somewhere between 0.06-0.37 lb (27.2-167.8 g). An adult specimen of such weight would be half as heavy as a billiard ball.

What are the male and female names of the species?

There are no distinct names for the males and females of their species.

What would you call a baby rainbow smelt?

A baby rainbow smelt does not have a distinct name and is very unimaginatively called a young smelt.

What do they eat?

Newly hatched young smelt fishes feed on the distribution of copepods and cladocerans and indulge in rotifers, eggs, and algae on the side. After they become adults their diet usually includes mysid shrimps, decapods, copepods, crabs, squid, worms, amphipods, a variety of small fish, and shellfish found in rivers or seas.

Are they dangerous?

When faced with humans, rainbow smelts are anything but dangerous even in large fisheries. In fact, humans were responsible for harshly bringing down the populations of rainbow smelt not too long ago. With that said, rainbow smelts have been studied a lot to measure their impact on various species and their spawning area in their ecosystem. Various studies have named them to be an invasive species in certain areas where they prey upon and bring down the numbers of certain native species.

Would they make a good pet?

Rainbow smelts need to constantly shift from saltwater to freshwater lakes, rivers, streams, and water bodies. This is done with the help of fast moving waters and hence it is not feasible to keep such fishes as pets.

Did you know...

Rainbow smelts have prominent teeth on the tongue and have a small adipose fin absent in Alaskan smelts.

Is Rainbow smelt an invasive species?

Although safe in an otherwise separate environment, when fisheries of species like rainbow smelt enter a certain ecosystem, it can wreak havoc in the populations of native species. They are therefore called invasive species. Several examples of rainbow smelt acting as an invading species were observed in various areas where it was either introduced or found itself. Native species often find themselves competing with or predated by invasive species and find their numbers dwindling in no time. As such, rainbow smelt uses its teeth and prey on a range of species namely Yellow Perch, Walleye, Lake Herring, Bloater, Whitefish, Lake Trout, and Slimy Sculpin. They are also thought to be the contributors to the extinction of the native Blue Pike.

How did rainbow smelt get to Ontario?

Rainbow smelt was first introduced intentionally via its eggs to Crystal Lake in 1912. Being a weak swimmer, the Rainbow Smelt drained into Lake Michigan. From here it rapidly spread itself across the many Great Lakes and its tributaries. Similarly, when rainbow smelts were introduced intentionally in Finger Lakes, New York in 1917, they did not stop there. Using the many natural waterways, the rainbow smelt found itself in Lake Ontario where it was first reported in the year 1929.

Here at Kidadl, we have carefully created lots of interesting family friendly animal facts for everyone to discover! For more relatable content, check out these arapaima facts and chum salmon facts pages.

You can even occupy yourself at home by coloring in one of our Rainbow Smelt coloring pages.



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