Smelt, Cucumber smelt, Salmo eperlanus (Linnaeus, 1758)

European smelt are opportunistic feeders, consuming copepods and cladocerans (Northcote and Hammar 2006). With increasing size and age, its food changes from small zooplankton to larger crustaceans and in some cases to fish and cannibalism (Nilsson 1979; Svärdson et al. 1988).  According to Sterligova (1979), European smelt also eat vendace larvae and fry (Jurvelius et al. 2005). Young European smelt are efficient planktivorous fish that can affect the size structure of the zooplankton community by size selective predation (van Densen 1985).

European smelt has both landlocked and anadromous forms. Landlocked individuals spawn in the spring in the littoral zone of lakes and return to the shore in autumn when the water temperature drops (Ilmast et al. 2021). Anadromous individuals migrate to rivers in April–June to spawn on sandy or sandy rock bottoms <3 m in depth (Sendek and Bogdanov 2019). Cannibalism is most likely to occur during spawning when both adults and larvae are present in large numbers (Ilmast et al. 2021). In a laboratory experiment, optimal hatching success was achieved in low salinity waters (0–10 ppt) and temperatures (5–10?), with no larva surviving to first feeding at 20 ppt (McCarthy et al. 2020). This species is highly fecund with a mean fecundity of 56,603 eggs/female (Hutchinson and Mills 1987). European smelt also exhibits relatively high rates of hermaphroditism: 2.6% of fish from the Elbe were hermaphroditic, and capable of self-fertilization, with other reports at 3.7% (Hutchinson 1983). This species reaches maturation at 2–4 years (Arula et al. 2017; Ilmast et al. 2021) and can live for 9–12 years (Ilmast et al. 2021).

Potential pathway(s) of introduction: Transoceanic shipping

European smelt live and spawn in the Elbe River (Thiel and Potter 2001), which is an extremely busy shipping route.  In the Netherlands, European smelt larvae survive transport in water pumped from Lake llsselImeer to the Frisian lake district to maintain a constant water level for agricultural purposes (Lammens et al. 1985). There was found to be 80% survival of European smelt after intake of a cooler water inflow to a power plant through a screen system (Rohlwing et al. 1998). Thus this species is considered likely to survive transport in a ballast tank.

Osmerus eperlanus has been introduced into several Scandinavian lakes, but not elsewhere. This species has not been reported to spread from the landlocked lakes into which it has been introduced.

Osmerus eperlanus has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: High).

European smelt live in large lakes in Finland, Sweden, Norway, Denmark, Poland and Russia (Nellbring 1989) with conditions similar to the more oligotrophic of the Great Lakes. Scandinavian lakes would have similar temperature regimes as the Great Lakes. Congeneric species (Osmerus mordax) have already been introduced into the Great Lakes and spread throughout the region (Nellbring 1989). This indicates (though does not guarantee), the suitability of the Great Lakes for this species' survival and spread. European smelt are tolerant of a wide salinity range. European smelt are unlikely to benefit from the effects of climate change as they are a coldwater species.

European smelt are opportunistic feeders, likely to readily find sufficient food in the Great Lakes. This species has a relatively high rate of hermaphroditism and can be self-fertile. European smelt are commonly consumed by predatory fish and birds that are abundant in the Great Lakes (Cremona et al. 2018). However,  European smelt biology and ecological plasticity, reproductive capacity, and efficient habitat use allow it to withstand predation and thrive (Hammar et al. 2018). Thus, predation may slow or prevent the establishment of this species. European smelt and rainbow smelt are competitors in their native ranges, and rainbow smelt is partially attributed to European smelts' limited expansion into the Arctic (Artamonova et al. 2020). Because rainbow smelt have already invaded and established in the Great Lakes, it may hinder the invasion success of European smelt.

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

European smelt are a strong competitor for zooplankton, and can outcompete native fishes and alter food webs. In Lake Vesijarvi, Finland, the intentional aeration of the lake to combat cyanobacteria blooms resulted in the dominance of native populations of European smelt and the decline in native perch and cyprinids due to food competition (Ruuhijarvi et al. 2020). The introduction of European smelt into a large lake in Norway and its numerical dominance led to a reduction in abundance of native planktivorous European whitefish (Coregonus lavaretus) and Arctic char (Salvelinus alpinus) due to competition. European smelt likely contributed to an increased abundance of small prey fish for brown trout, whose diet shifted earlier to piscivory with a more pelagic focus and thus benefited from increased growth rate. Ultimately, European smelt shifted the food web and fish community in the lakes from a littoral to a more pelagic base (Eloranta et al. 2019). European smelt can also reach very high densities (Northcote and Hammar 2006).  Jurvelius et al. (2005) did a study of European smelt in 5 Finnish lakes: in four lakes the proportion of smelt was more than 60%. Unfortunately, this article is in Russian and has not been translated apart from the abstract. Illegally stocked European smelt in Lake Masolzero, Russia have become the dominant food item for predatory fish in the lake (Ilmast et al. 2021). European smelt was accidentally introduced (in or before 1968) into the ecosystem of the Syamozero lake in Karelia (north-western Russia) due to its recent eutrophication and spike in productivity. The population of this species had reached a high density and caused serious changes in the structure and trophic relationships of the fish community of the Syamozero ecosystem (Ieshko et al. 2000). It became the dominant fish species, displacing the native vendace Coregonus albula due to food competition. Food web dynamics shifted from zooplankton-vendace-predators to zooplankton-smelt-pikeperch. Then, when nutrient levels declined in the 1990’s European smelt populations also decreased by a combination of overwhelming Glugea hertwigi infection and predation by large piscivores. Shortly after the extirpation of European smelt, vendace populations recovered in the Syamozero ecosystem (Anikieva et al. 2022).

The resource partitioning of the bream (Abramis brama) and eel (Anguilla anguilla) populations in Lake Tjeukemeer, The Netherlands, was related to the variation in abundance of their most important food organisms, Daphnia hyalina and larval chironomids. Niche shifts of both bream and eel populations were related to the abundance of young planktivorous fish, particularly European smelt. When these fish were abundant the D. hyalina population was dominated by small individuals and bream switched from a planktivorous to a benthivorous diet, the condition of mature bream deteriorated, and its gonads developed poorly. Under these circumstances the eel population switched from a diet of chironomid pupae and molluscs to one of predominantly fish. The condition of eels smaller than 35 cm decreased as? the chironomid population decreased in numbers and biomass (Lammens et al. 1985). Thus European smelt has the potential to disrupt resource partitioning among native species and its introduction may have consequences for native populations of American eel (Anguilla rostrata).

The congeneric rainbow smelt, Osmerus mordax, is currently established in the Great Lakes and is reported to have a variety of environmental impacts. Similar impacts on the Great Lakes could be expected from European smelt if introduced. 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. Rainbow smelt were implicated in the decline of cicos by predation on their larvae (Myers et al. 2009). Hrabik et al. (1998) found evidence of competition for food between introduced rainbow smelt and native yellow perch (Perca flavescens) in Wisconsin lake habitats (Fuller 2013).

European smelt is a paratenic host for the parasitic nematode, Anguillicola crassus (causing swimbladder lesions in eels); in Europe, European smelt transmits the parasite when preyed upon by eels (Haenen et al. 1994). The Baltic and North seas and coastal lake populations of European smelt are commonly infected with Anisakdiae nematodes, however the nematodes require salt water for part of their life cycle (Dziekonska-Rynko et al. 2018) and would be unlikely to be a threat in the Great Lakes. In European smelt’s native range, it is a host for the microsporidian Glugea hertwigi, and is found in some German Rivers and the coast of the North Sea (Costa et al. 2016). Glugea hertwigi infects smelt species and has already been found in the Great Lakes in rainbow smelt (Kipp et al. 2022). A novel herpesvirus was discovered in European smelt, but the health impacts of the virus are unknown (Jakob et al. 2010).

Current research on the potential for socio-economic impacts to result from Osmerus eperlanus if introduced to the Great Lakes is inadequate to support proper assessment.

European smelt is the most important fish intermediate/transport host of the sealworm Pseudoterranova decipiens in the Elbe estuary and probably also in adjacent coastal waters of the Wadden Sea (Rohlwing et al. 1998; Karl 2006). Sealworms are potentially capable of causing anisakiasis-like symptoms in humans (e.g. abdominal pain, nausea, fever) when consumed in lightly cooked or raw fish products (pseudoterranovosisi e.g. Rae 1963; Margolis 1977; Yu et al. 2001; McClelland 2002; Audicana and Kennedy 2008). However, this parasite requires seals to complete its life cycle (Kuhn et al. 2013).

Osmerus eperlanus has the potential for moderate beneficial impact if introduced to the Great Lakes.

The commercial value of European smelt is low in Finnish lakes (Jurvelius et al. 2005). It supports a key commercial fishery for St. Petersburg in the Gulf of Finland, but it has been in a state of decline since 1992. However, recent efforts to restore the smelt fishery have been slowly improving catch rates since 2017 (Sendek and Bogdanov 2019). Smelt (Osmerus spp.) is an important food item for predatory fish species like pike-perch, brown trout and landlocked salmon (Peltonen et al. 1999; Heikinheimo et al. 2002; Keskinen and Marjomäki 2004; Jurvelius et al. 2005). Evidence from congeneric species: Havey (1973) reported increased growth of landlocked Atlantic salmon following the introduction of rainbow smelt as a forage species in a lake in Maine (Fuller 2013). Rainbow smelt have been an important dietary item for salmon and trout in the Great Lakes, but have been declining in importance as other prey species become more abundant (Brandt 1986; Jacobs et al. 2013).

In Canada, the use or possession of fish as live bait in any province other than from which it was taken is prohibited (SOR/93-55). It is illegal to bring any live fish into Ontario for use as bait (SOR/2007-237). This species is not on the Illinois Aquatic Life Approved Species List and if it is not otherwise native to Illinois it is illegal to be imported or possessed alive without a permit (515 ILCS 5/20-90).

Note: Check federal, state, and local regulations for the most up-to-date information.

Control

Biological

European smelt would likely become a suitable prey option for many of the piscivorous fish in the Great Lakes that feed on rainbow smelt (Osmerus mordax). These predators include: Atlantic salmon (Salmo salar), lake trout (Salvelinus namaycush), Brook trout (Salvelinus fontinalis), Coho salmon (Oncorhynchus kisutch), Chinook salmon (Oncorhynchus tshawytcha), rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), Splake (Salvelinus namaycush x fontinalis), burbot (Lota lota), walleye (Sander vitreus), northern pike (Esox lucius), and many other freshwater piscivores (Stewart et al. 1981; Brandt and Madon 1986; Crossman 1991; He and LaBar 1994; Kirn and LaBar 1996; GLMRIS 2012). Additionally, piscivorous birds in Europe have shown to feed heavily on European smelt indicating that birds native to the Basin such as Ibis, Great blue heron, and grebes would also consume European smelt (Piersma et al. 1988).

Several studies have noted the susceptibility of European smelt to microbial agents such as the Comet herpes virus of smelt, microsporidian parasites (e.g. Glugea spp. or Pleistophora ladogensis) and sealworm (Pseudoterranova decipiens) (Schrader 1921; Sprengel and Luchtenberg 1991; Jakob et al. 2010). Sprengel and Luchtenberg (1991) observed that smelt infected with the muscular parasites, P. ladogensis (Microsporal) and P. decipiens (Nematoda), exhibited a significant reduction in swimming speed. This implies that the infected smelt are subject to higher predation rates due to their diminished ability to escape. However, the use of pathogens or parasites to control European smelt is not practical due the potential impact these could have on native species and humans.

Physical

Various types of physical controls that have been used to control rainbow smelt and other non-indigenous fish might also be effective in managing European smelt. Patrick et al. (1985) observed that air bubble curtains have been successful in deterring rainbow smelt, alewife, and gizzard shad—especially when used in conjunction with strobe lights. Other types of physical treatments have been employed in fish control include reservoir drawdowns, traps, nets, electrofishing, and combinations of these treatments. Through their review of fish control methods, Meronek et al. (1996) observed that projects that utilized nets were the most successful of the previously listed physical treatments.

Chemical

Of the four chemical piscicides registered for use in the United States, rotenone and antimycin have been used in the majority of chemical control projects and have had varied success rates for different species and different bodies of water (Marking et al. 1983; Boogard et al. 1996; Maronek et al. 1996; GLMRIS 2012). Marking et al. (1983) found that the three most effective registered chemicals for potential use in control of rainbow smelt eggs and larvae are rotenone, potassium permanganate, and chlorine, respectively. The relatedness of rainbow smelt and European smelt might indicate that these treatments will have a similar effect on European smelt, especially since chemical piscicides typically are not species-specific. However, sensitivity to treatments varies among species so this assumption is not necessarily true (Boogard et al. 1996). Therefore, it is imperative to understand the physiology and ecology of European smelt, as well as the characteristics of the specific environment such as water quality and water volume, which might affect the success of piscicides in the control of European smelt (Marking et al. 1983; Ling 2003; Lennox et al. 2015).

Other

The temperature and dissolved oxygen requirements for European smelt can provide insight on how an introduced population might be controlled. European smelt is generally a coldwater species and mortality rate seems to be positively associated with increases in water temperature (Kangur et al. 2005; Kangur et al. 2007b; Keskinen et al. 2012). This was seen in Lake Peipsi (Estonia/Russia) where high temperatures negatively affected the catch rate of Smelt 1 and 2 years later and long periods of high water temperatures (>20?) led to extensive fish kills (Kangur et al. 2005; Kangur et al. 2007b). Keskinen et al. (2012) demonstrated how long-term warming trends threaten the survival of European smelt. They observed that the pelagic habitat of European smelt was restricted due to increases in water temperature and decreases in dissolved oxygen. Similar observations were made by Gerasimov et al. (2018) in a Russian lake. In two Dutch lakes, Keller et al. (2020) found a growing mismatch in the temporal feeding habits of European smelt and zooplankton availability due to the warming effects of climate change.  Therefore, climate change may control or limit the establishment of European smelt in the Great Lakes due to their species-specific requirements for temperature and dissolved oxygen and cascading impacts on food web dynamics.

Note: Check state and local regulations for the most up-to-date information regarding permits for pesticide/herbicide/piscicide/insecticide use.