Rainbow Smelt

Diet and feeding

The FishTraits compilation records these diet categories for this species: invertebrates or larval fish; larger animal prey (a source category covering fish, crayfish, crabs, or frogs). These are broad categories, not a claim that every individual consumes every example in a category.

Reported feeding positions include bottom feeding and surface or water-column feeding. The compilation combines published observations; diets can vary with age, locality, and available food.

Habitat preferences

Reported habitat associations include medium to large rivers, streams and small rivers, creeks, still-water habitats.

The source records associations with gravel, cobble. An association indicates reported use, rather than an exclusive requirement.

The species is classified as tolerant of a broad range of salinities. This flag does not specify a salinity range for aquarium care.

Reproduction and parental care

The compilation reports a representative maturity age of 2.5 years. Its maturity field summarizes mean, median, or modal estimates, usually for females; male estimates can be used when female data are unavailable. It is not a fixed age at which every fish first breeds.

Batch or serial spawning has been reported somewhere in the species’ range. This does not establish the same spawning pattern for every population.

Recorded spawning months are Mar, Apr for the source’s reporting region (PA). This is a regional calendar, not a range-wide schedule.

The reproductive-guild classification includes spawning on open substrates without guarding the brood.

Size and recorded longevity

FishTraits reports a maximum total length of 35.6 centimetres. Some entries use an estimated asymptotic length; this value should not be treated as a certified record catch.

Recorded longevity in the compilation is 5 years. Wild observations were preferred, but captive records were accepted where wild records were unavailable, and unspecified records were assumed wild. The value is not a guaranteed wild lifespan or an aquarium life expectancy.

Spawning movements

The compilation records significant spawning-related movement. Its combined migration flag covers movements within fresh water as well as between rivers and the sea; this flag alone does not establish which migration pattern applies.

Identification and appearance

Rainbow Smelt have a silvery, pale green back and a white underside. The sides of the fish are iridescent purple, blue, and pink with a bright silvery stripe. They have less than 75 scales on the lateral line, which are easily removed. Rainbow Smelt have three characteristic fins, a dorsal in the middle of the back, an adipose, and a deeply forked rear tail fin. The snout is pointed with well developed, canine-like teeth on the tongue and roof of the mouth. Rainbow Smelt resemble the minnow family (Cyprinidae spp.), Lake Whitefish (Coregonus clupeaformis) and Cisco (C. artedi), however, minnows lack an adipose fin and Lake Whitefish and Cisco have deeper bodies than Rainbow Smelt but no teeth on the roof of their mouths or tongues. See Scott and Crossman (1973); Becker (1983); Smith (1985); Page and Burr (1991).

Native range

Atlantic drainages from Lake Melville, Newfoundland, to Delaware River, and Pennsylvania; Arctic and Pacific drainages from Bathurst Inlet, Northwest Territories, to Vancouver Island, British Columbia. Also, Pacific drainages of Asia (Page and Burr 1991). The origin of Osmerus mordax in Lake America is disputed, as they are thought to be either native or introduced from the Atlantic through the Erie Canal (Mills et al. 1993). Another alternative is that O. mordax migrated downstream from the upper Great Lakes, where it is considered nonindigenous.

Habitat and ecology

Spawning of Rainbow Smelt occurs after ice-out in early spring once water temperatures reach ~4.4°C with a peak at 10°C (Becker, 1983). In the Great Lakes, spawning occurs in tributary streams and occasionally on the shoreline. Eggs of the Rainbow Smelt are adhesive, negatively buoyant, and adhere to substrate until hatching 2 to 3 weeks later (Scott and Crossman 1973; Becker 1983). Age of maturation ranges between 1 to 4 years amongst populations (McKenzie 1958; Murawski and Cole 1978) and life expectancy can reach 8 years (Bailey 1964; Kirn and Labar 1996). They are sexually dimorphic, with females growing larger and living longer than males (McKenzie 1958; Bailey 1964).

Rainbow Smelt can survive in a broad range of environmental conditions. They inhabit temperatures from -1.8°C to around 20°C (Nellbring 1989; Raymond 1995), and can acclimate to extreme cold (< 5°C) by producing an antifreeze protein, glycerol, to facilitate faster-swimming speeds and increased muscle function (Coughlin et al. 2019). A laboratory study that assessed embryonic and larval Rainbow Smelt survival in response to various abiotic factors (dissolved oxygen, pH, salinity, nitrates, and phosphates) found that their survival was only significantly reduced when dissolved oxygen levels were less than 20% and the pH<5 (Fuda et al. 2007). However,a review of data from 8,842 Ontario lakes found that Rainbow Smelt were only caught in lakes with a pH>6 despite adequate opportunity to invade lakes with lower pH values (Evan and Loftus 1987).

Rainbow Smelt are zooplanktivorous at small sizes (<150 mm SL), consuming copepods and cladocerans (e.g., Daphnia and Bosmina); while at larger sizes (>150 mm SL) diet includes benthic crustaceans, and larval and small fishes (Sheppard et al. 2012). They are an important forage fish for many predators, including Atlantic Salmon (Salmo salar), Walleye (Sander vitreus), and Lake Trout (Salvelinus namaycush) (Gorman 2019).

Introduction history

Two means have been proposed to explain the introduction of Rainbow Smelt into the Missouri and Mississippi rivers. It may have spread from Lake Michigan via the Chicago sanitary canal to the Illinois River and then to the Mississippi and Missouri rivers (Burr and Mayden 1980). Alternatively, the species may have gained access to these rivers as a result of a stocking at Lake Sakakawea, North Dakota, in 1971 (Bouc 1987; Mayden et al. 1987; Holton 1990). The second explanation seems more plausible because of a lack of records from the Illinois River. Records of first occurrences in other areas include the Mississippi River, Illinois, and Kentucky, 1978; Mississippi River, Louisiana, 1979; Mississippi River, Tennessee, and Arkansas, 1980; Missouri River, Missouri, 1980; Missouri River, Kansas, 1982 (Mayden et al. 1987). Mayden et al (1987) provided a map of the species' distribution, dates of first observation in new areas, and possible introduction pathways. The species was originally introduced into Lake Sakakawea, North Dakota, as forage for Salmonids (Mayden et al. 1987).

Ecological impacts

Dominant prey form for salmonids; contributed to extinction of Blue Pike; affect imperiled species (U.S.EPA 2008; Crossman 1991). In the Great Lakes, Rainbow Smelt compete with Lake Herring Coregonus artedii for food (Becker 1983). Christie (1974) supplied some evidence to support this, correlating lake herring decline with smelt increases in most of the lakes. Todd (1986) also reported that smelt may be partially responsible for the decline of whitefish Coregonus spp. in the Great Lakes. Havey (1973) reported increased growth of landlocked Atlantic Salmon following the introduction of smelt as a forage species in a lake in Maine. Hrabik et al. (1998) found evidence of competition for food between introduced Rainbow Smelt and native Yellow Perch Perca flavescens in Wisconsin lake habitats. Stedman and Argyle (1985) found the diet of O. mordax to include young-of-the-year fish. The species that were consumed by O. mordax depended upon the prey availability (Stedman and Argyle 1985). Stedman and Argyle (1985) discovered that in Lake Michigan in late October of 1982, O. mordax consumed Bloaters (Coregonus hoyi) and Alewives (Alosa pseudoharegus). The authors also noted that although O. mordax does not appear to have had an impact on Bloater populations in the last five years, future impact is possible. A study on nighttime consumption of O. mordax in Lake America revealed their primary food source to be Slimy Sculpin (Cottus cognatus) and opossum shrimp (Mysis relicta) (Brandt and Madon 1986). Juvenile Lake Trout (Salvelinus namaycush) rely heavily on C. cognatus, competing directly with O. mordax, while adult S. namaycush consume O. mordax (Brandt and Madon 1986). The authors point out that S. namaycush may be a keystone predator in the relationship between O. mordax and C. cognatus. Rainbow Smelt contain high levels of thiaminase, which reduces absorption and assimilation of thiamine in predators such as salmonids can cause reduced body condition, swim performance, and other potenial impacts (Houde et al. 2015)