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Rainbow smelt

Rainbow smelt

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The rainbow smelt, Osmerus mordax, is an anadromous species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Osmeridae. The distribution of Osmerus mordax is circumpolar
The term circumpolar may refer to:* circumpolar navigation: to travel the world "vertically" traversing both of the poles* Antarctic region** Antarctic Circle** the Antarctic Circumpolar Current** Subantarctic** List of Antarctic and subantarctic islands...

. The rainbow smelt was introduced to the Great Lakes, and from there has made its way to various other places. Walleye
Walleye is a freshwater perciform fish native to most of Canada and to the northern United States. It is a North American close relative of the European pikeperch...

, trout
Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...

, and other larger fish prey on these smelt. The rainbow smelt prefer juvenile ciscoes
Cisco (fish)
The ciscoes are salmonid fish of the genus Coregonus that differ from other members of the genus in having upper and lower jaws of approximately equal length and high gillraker counts...

 and other small organisms such as zooplankton. They are spring spawners and prefer clean streams with light flow and light siltation. The rainbow smelt face several barriers. They are weak swimmers and cannot overcome most fish ladders. This prevents them from making it past the dams to the headwater streams where they need to spawn. The rise in erosion and dams help to decimate the smelt population in the 1980s. There are currently plans to try to reduce damming and to help control erosion. With current efforts to reduce the human impact on these and many other affected species the population is back on the rise.


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 full grown, the rainbow smelt is between 7 and 9 in (17.8 and 22.9 cm) long and weighs about 3 ounces (85 g), and ones over 12 inches (30.5 cm) are known.

Distribution and habitat

The rainbow smelt has been wide spread across North American watersheds.
The North American native range of the rainbow smelt extends through the Atlantic drainages between New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...

 and Labrador
Labrador is the distinct, northerly region of the Canadian province of Newfoundland and Labrador. It comprises the mainland portion of the province, separated from the island of Newfoundland by the Strait of Belle Isle...

 to Arctic and Pacific drainages of Vancouver Island
Vancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...

. The rainbow smelt has been introduced into water bodies in the U.S. states of Colorado, Connecticut, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, New Hampshire, New York, North Carolina, North Dakota, Ohio, Pennsylvania, South Dakota, Tennessee, Vermont, Virginia, Wisconsin. Landlocked populations were historically known in Maine, and fish from one of these populations were introduced to Crystal Lake
Crystal Lake (Michigan)
Crystal Lake, the largest lake of this name in Michigan, is located near Lake Michigan in Benzie County about 25 miles southwest of Traverse City and about 2 miles northeast of Frankfort at . It measures approximately 2.5 by 8 miles , and has a maximum depth of 165 feet . At , it is Michigan's...

, Michigan and then spread to the Great Lakes.

Rainbow smelt invaded the Great Lakes watershed through an intentional introduction of eggs to Crystal Lake in 1912. This lake drains into Lake Michigan, from which fish escaped into Lake Michigan and spread quickly throughout the Great Lakes and their tributaries. Early records documenting the smelt's range expansion in the Great Lakes include Lake Michigan, Lake Erie, Lake Huron, Lake Ontario, and Lake Superior. Rainbow smelt were first reported from Lake Ontario in 1929, and probably reached it by dispersal along natural waterways from the Finger Lakes
Finger Lakes
The Finger Lakes are a pattern of lakes in the west-central section of Upstate New York in the United States. They are a popular tourist destination. The lakes are long and thin , each oriented roughly on a north-south axis. The two longest, Cayuga Lake and Seneca Lake, are among the deepest in...

, New York, where they were intentionally introduced in 1917. The ability of rainbow smelt to disperse is determined by the connectivity of lakes, the ability of smelt to move through connecting streams, and the suitability of connected lakes as habitat. Rainbow smelt are weak swimmers so they cannot make it over fish ladders. This has helped to prevent an even wider spread of their range.

Rainbow smelt occur in rivers, coastal areas and ponds. In their anadromous territories, they spend the summers along the coast, normally in waters no more than 20 feet (6.1 m) deep and no more than 1 miles (1.6 km) from shore. They overwinter under the ice in estuaries, producing an antifreeze protein and glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...

. In the spring, they spawn at night in small streams, often ones that go dry in the summer.


In 1885 Stedman and Argyle found that Osmerus mordax consumed bloaters (Coregonus hoyi
Coregonus hoyi
The bloater is a species of freshwater whitefish in the family Salmonidae. It is a silvery-coloured herring-like fish, long. It is found in most of the Great Lakes and in Lake Nipigon, where it inhabits underwater slopes....

) and alewives (Alosa pseudoharengus) however they also stated that this predator had not impacted the population of bloaters but that impact could be a possibility. A 2003 study by Horppila et al. shows that smelt densities can exceed 40,000 individuals per hectare and may create a large predation pressure on the lake. Horppila et al. also states that a single smelt can consume between .12 grams and .14 grams. Another study showed that in Lake Ontario the primary food sources for rainbow smelt were slimy sculpin
Slimy Sculpin
The slimy sculpin, Cottus cognatus, is a freshwater species of fish that inhabits cool, rocky streams, rivers and lakes throughout northern North America and eastern Siberia. The slimy sculpin is found in freshwater and sometimes brackish water in areas with rocky or gravel type bottoms...

s (Cottus cognatus) and opossum shrimp
Opossum shrimp
Neomysis americana is an "extremely common" species of opossum shrimp along the Atlantic coast of North and South America. The species has a disjunct distribution, being present in an area extending from the Saint Lawrence River to Florida, and separately in parts of Argentina...

 (Mysis relicta), but nothing was said on whether this predation had significant impact on the populations. In 1973 Havey reported that there was increased growth in landlocked Atlantic salmon
Atlantic salmon
The Atlantic salmon is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the north Atlantic and the north Pacific....

 populations after the introduction of the smelt. It was also shown by Brandt and Madon in 1986 that adult lake trout
Lake trout
Lake trout is a freshwater char living mainly in lakes in northern North America. Other names for it include mackinaw, lake char , touladi, togue, and grey trout. In Lake Superior, they can also be variously known as siscowet, paperbellies and leans...

 (Salvalinus namaycush) could be a keystone predator species for the smelt. Hrabik et al. (1998) found evidence of competition for food between introduced rainbow smelt and native yellow perch
Yellow perch
The yellow perch is a species of perch found in the United States and Canada, where it is often referred to by the shortform perch. Yellow perch look similar to the European perch, but are paler and more yellowish, with less red in the fins. They have six to eight dark, vertical bars on their sides...

 (Perca flavescens) in Wisconsin lake habitats, and smelt may be partially responsible for the decline of Great Lakes whitefish (Coregonus
Coregonus is a diverse genus of fish in the salmon family . The type species is the common whitefish . The Coregonus species are known as whitefishes...

spp.). The U.S. EPA stated in 2008 that they believe the smelt contributed to the extinction of the blue pike (Stizostedion vitreum glaucum) by outcompeting for food. Acidity may alter smelt distributions because they were not found in small lakes with pH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 less than 6.0 in several surveys. Because of snowmelt, rainbow smelt eggs might be exposed to lethal pH decreases in poorly buffered lakes.

Life history

Rainbow smelt are anadromous, ascending from saltwater to freshwater to spawn. Smelt are also capable of completing their life history exclusively in freshwater. Landlocked adult rainbow smelt spawn shortly after ice-off at night in the lower reaches of streams. Shaw found in his research that no shoreline spawning had ever occurred. McKenzie states that the number of eggs extruded by a female is positively related to its size and Nellbring stated in his 1989 research that the eggs are adhesive and attach to substrates such as gravel, sand, mud, or submerged vegetation. Eggs are left unattended and hatch in 1–4 weeks, depending on water temperature. The time to sexual maturity is dependent on food supply and water temperature and abundant food and warmer temperatures encourage faster growth. Crossman and Scott state that in optimal conditions and large lakes, rainbow smelt may reach 35.6 centimetres (14 in) and can live for over seven years.


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
Charles River
The Charles River is an long river that flows in an overall northeasterly direction in eastern Massachusetts, USA. From its source in Hopkinton, the river travels through 22 cities and towns until reaching the Atlantic Ocean at Boston...

 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
Game fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...

 and the spring smelt run is a tradition in many parts of their distribution. Fishing for rainbow smelt using a gill net is a popular activity along the city of Chicago's lakefront.


The populations of the rainbow smelt in areas where it has been introduced, such as the Great Lakes, have been increasing in many regions, even with efforts to control its spread. Several things are being done to manage this species. Massive fish removal by over-fishing reduced the rainbow smelt populations in some lakes by the 1980s. Some people are taking a chemical approach to this growing problem, using Rotenone
Rotenone is an odorless chemical that is used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the roots and stems of several plants such as the jicama vine plant...

. Extoxnet describes Rotenone as "a slow-acting poison which interferes with the electron-transport system in the mitochondria. It acts as both a contact and stomach poison". While this is effective, it also harms other organisms and is unpopular with the public. Cox and Kitchell state that declines in smelt numbers following natural recovery or stocking of grown predator fish have been reported from lakes ranging in size from Lake Superior and Hessen found similar results in a small pond near Lillehammer
is a town and municipality in Oppland county, Norway, globally known for hosting the 1994 Winter Olympics. It is part of the traditional region of Gudbrandsdal. The administrative centre of the municipality is the town of Lillehammer. As of May 2011, the population of the town of Lillehammer was...

, Norway in 1983. This research shows that the reintroduction of large piscivores such as walleye can help lead to the reduction of chemicals and poison needing to be used.

This species should continue to be heavily monitored and managed. Random samples as well as plotted samples should be preformed to help gather a good estimation of population size and density, and should be done very widely. Boat shocking and gill netting would be two good ways to perform the sampling. In smaller areas backpack shockers and seines may be used. In Robinson's research seines were used successfully in collecting samples for research. Since these fish tend to heavily populate the Great Lakes boat shocking/gill netting would be the most productive way to gather information in a timely fashion. These fish have proven that given the right vector, whether human introductions or overflow into non-native streams, they can go almost anywhere. The heaviest amount of sampling should most likely occur in the Great Lakes and other northern reservoirs because this is where the largest populations tend to occur. This species should not be completely removed but it should be heavily managed. This is a good prey species for prized game fish but once the population gets out of control they can have a large impact on other important organisms. Introduction of large piscivores, such as walleye, seems to be working, and this method allows the reduction of poison and toxin use in the water.

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