Silurus glanis (Linnaeus, 1758)

Common Name: Wels Catfish

Synonyms and Other Names:

Sheatfish, European Catfish



Copyright Info

Identification: Silurus glanis is distinguishable by its large, scaleless, slime covered body, and six barbels - two of which are long and on the side of the mouth and the other four are on the lower jaw. It has a tiny dorsal fin, one anal spine, and paired pelvic and pectoral fins. Body is typically dark greenish-black with yellowish sides that results in a mottled pattern. The head is large and eyes are proportionally small (Kottelat and Freyhof 2007).


Size: Largest specimen recorded was 2.73 m long and 130 kg (Boulestreau and Santoul 2016). Eggs are large, between 1 to 3 mm in diameter (Copp et al. 2009).


Native Range: Silurus glanis’s native distribution extends from Germany eastwards through to Poland, up to Southern Sweden and down to Southern Turkey and north Iran stretching through the Baltic States to Russia (Greenhalgh 1999) and to the Aral Sea of Kazakhstan and Uzbekistan (Phillips and Rix 1988, Copp et al. 2009).


This species is not currently in the Great Lakes region but may be elsewhere in the US. See the point map for details.

Ecology: Individuals are usually strongly associated with areas with a high density of woody debris, boulders, low flow and tree roots (Abdullayev et al. 1976). The species, therefore, appears to prefer large water bodies with cryptic habitat (Britton et al. 2007). Silurus glanis has thrived in degraded habitat (Italy), such as canals that were eutrophic and turbid, without morphological complexity, and with sparse vegetation (Castaldelli et al. 2013). They also prefer artificially heated habitats (e.g., nuclear power plant discharge water) (Capra et al. 2018). This species is normally encountered throughout their native range in large rivers, lakes, and coastal areas of low salinity (<15 ppm), and primarily occupies highly productive, weedy lakes, and slow, deep lowland rivers. This species is known to shift during their first year of life from shoreline into mid channel habitats (Wolter and Vilcinskas 1996; Wolter and Freyhof 2004), which are important for reproduction and habitat partitioning between different age groups (Wolter and Bischoff 2001). During winter, it is relatively inactive and resides in deep holes, dens and crevices in the river bed; in lakes, it lies in the lower third of the water column or on soft mud (Lelek et al. 1964; Lelek 1987; Copp et al. 2009).

Silurus glanis occupies water temperatures from 0° to at least 30°C, though success may be limited in lower water temperatures (David 2006; Britton et al. 2007). Physiological optimum is between 25° and 27°C when the most activity occurs (Copp et al. 2009) and its relocation and home range size increases with higher water temperatures (Danek et al. 2016). Therefore, warmer water temperatures would benefit this species (David 2006). High levels of hemoglobin also make S. glanis relatively tolerant of pollution (Lelek 1987) and prolonged periods of hypoxia (Massabuau and Forgue 1995). Silurus glanis regularly tolerates dissolved oxygen levels of 3.0 to 3.5 mg/L and can withstand low levels of salinity (Copp et al. 2009). Further, they can inhabit eutrophic and turbid waters (Castaldelli et al. 2013).

Silurus glanis has well-developed non-visual sensors that make it well adapted to waters with low visibility (Copp et al. 2009), giving it a high degree of plasticity in various light regimes (Placinta et al. 2020).

Silurus glanis feeds primarily at night, and it is well documented that S. glanis takes advantage of its diet plasticity and ability to prey upon the most abundant available species of a suitable size within its habitat (Carol 2009; Syväranta et al. 2010; Martino et al. 2011; Castaldelli et al. 2013). Trophic position increases with size, with the largest individuals acting as apex predators (Rees 2020). Its preference is for shrimp and crayfish in rivers, and shrimp and fish in streams, with largest specimens feeding primarily on fish(Ferreira et al. 2019). The fast growth and large size of S. glanis makes them unlikely prey for other piscivores (Copp et al. 2009).

Males and females mature at 2–3 years and 1–2 kg. Mating pairs spawn in April to June (up through September in northern latitudes > 41°N) at temperatures between 18 to 22°C. Spawning occurs in shallower waters, including drainage channels and floodplains (Kottelat and Freyhof 2007; Copp et al. 2009; Rees 2020). Eggs are laid in nests made of plant material and are defended by males until larvae emerge after 2–3 days (Kottelat and Freyhof 2007). Total fecundity can range from 30,000 to 300,000 eggs per female, and average relative fecundity ranges between 13,000 and 20,000 eggs per kilogram (Yazici et al. 2018; Yesilcicek 2020). Adults are known to live upwards of 80 years (Kottelat and Freyhof 2007).


Means of Introduction: Silurus glanis has an unknown/low probability of introduction to the Great Lakes (Confidence level: Moderate).

Potential pathway(s) of introduction: Unauthorized Intentional Release

The import and sale of S. glanis to the United States was banned under the Lacey Act in 2016, however several hobbyist forums had posts seeking this fish since 2016, and one post indicated they had a specimen for sale in California, United States. As these claims cannot be verified, probability of introduction through this vector remains unknown. Due to the previous legality of their trade and extensive life span, an unknown number of specimens may still exist in the United States.

This species has been introduced to many European countries, including France, Italy, the Netherlands, Spain and the United Kingdom due to its popularity among anglers (Banarescu 1989; Krieg et al. 2000; Britton et al. 2007; Carol et al. 2007, 2009; Copp et al. 2009; Alp et al. 2011). This includes intentional, unauthorized introduction. Silurus glanis is farmed in Austria, Bulgaria, Croatia, Czech Republic, France, Hungary, Greece, Macedonia, Poland, and Romania (Linhart et al. 2002).

This species has spread rapidly through human introductions, but slowly via natural dispersal (Copp et al. 2009).  Introductions of S. glanis in Europe are facilitated by illegal stockings and natural dispersal intensified by climate change (Cerri et al. 2018; Rees 2020). The European Nonnative Species in Aquaculture Risk Analysis (ENSARS) listed S. glanis as a moderately low risk for introduction (but a moderate risk for establishment) in the UK, however a survey of anglers revealed a lack of awareness of the damages S. glanis will have if introduced (Copp et al. 2016; Rees et al. 2017). The Fish Invasiveness Screening Kit (FISK) listed S. glanis as a high risk of invasion in Croatia, Slovenia, and South Africa (Piria et al. 2016; Marr et al. 2017). The invasiveness of S. glanis is only expected to increase due to rising water temperatures from climate change (Rees 2020). As S. glanis encounters new environments, it is predicted to increase its use of space, which accelerates its dispersal rate (Cote et al. 2010; Chappele et al. 2012). Additionally, S. glanis individuals that have been translocated via traditional stocking methods were shown to have decreased fitness and altered behaviors (Monk 2020).


Status: Not established in North America, including the Great Lakes.

Silurus glanis has a high probability of establishment if introduced to the Great Lakes (Confidence level: High).

It is likely S. glanis would be able to survive in the Great Lakes since it tolerates a range of climates including many of the conditions found in the Great Lakes. Its mild salinity tolerance may give it a competitive advantage over native species limited to freshwater if salinization increases in the Great Lakes (Copp et al. 2009). Silurus glanis is able to adjust its diet based on availability of prey making it adaptable to Great Lakes food webs. This species is a nest guarder, which gives it an advantage over other native fish that do not nest guard young, and it has a long lifespan.

In countries currently invaded by S. glanis, spread and establishment can be rapid, particularly in the Iberian peninsula. Silurus glanis has spread via natural dispersal or stocking over 700 km in the River Tagus, Spain between their first introduction in 1998 and 2015 (Gago et al. 2016). Since 1974, S. glanis has spread into 6 of 7 of the watersheds in the Ebro basin, Spain, likely accelerated by angling activities and governmental water transfers (Parrando et al. 2018). Overall, the fishing effort and harvest of S. glanis has increased with angling and air temperature in Central Europe between 1986-2017 (Lyach and Remr 2019).


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

EnvironmentalSocioeconomicBeneficial



Silurus glanis has the potential for high environmental impact if introduced to the Great Lakes.

In early stage invasion sites, S. glanis mainly consumed fish because of a high abundance of small cyprinid species, such as Roach and Bleak (Carol et al. 2007). In contrast, crayfish was the main prey of catfish in advanced stage invasion sites and the ontogenetic shift to piscivory was delayed until the catfish grew larger. Accordingly, these advanced stage invasion reservoirs had size structures dominated by larger sizes of Common Carp. Although further data are needed to see how frequent these patterns are, the results strongly suggest that at the early stages of invasion, catfish grow faster and are in better condition because they prey more on fish. As invasion proceeds, however, the catfish reduce fish numbers, particularly of smaller fish, indirectly favoring crayfish and eventually resulting in their own reduced growth rates (Carol 2009).

In addition to fish prey, another likely ecological impact of catfish is on some groups of waterbirds, especially in the Anatidae family. A few birds have been observed in the catfish stomachs, (Omarov and Popova 1984, Czarnecki et al. 2003). Carol et al. (2009) also found that waterbird abundance varied significantly with the invasion sequence (advance stage correlated with lower bird abundance) and this did not appear to be correlated or confounded by abiotic factors (such as reservoir size, altitude or trophic state). The significantly lower abundance of waterbirds in reservoirs with catfish could be due to either a direct ecological impact (predation) by catfish and/or to avoidance behavior by waterbirds to reduce predation risk (Carol 2009).

Silurus glanis takes advantage of its diet plasticity and ability to prey upon the most abundant available species of a suitable size within its habitat (Carol 2009; Syväranta et al. 2010; Martino et al. 2011). If established as an apex predator in an ecosystem, S. glanis can heavily impact other species through predation and food web alterations (Vejrik et al. 2017a). Silurus glanis has even been reported to consume Atlantic salmon (Salmo salar) in France (Boulêtreau et al. 2017). In French rivers, an invasion of S. glanis impacted some fish communities, but not on a generalised basis as some rivers were productive enough to support both invasive species and natives (Guillerault et al. 2015). Silurus glanis may adapt foraging behaviors in new habitats and introduced populations have been observed to breach onto land to capture birds (Syväranta 2010; Cucherousset et al. 2012).

Silurus glanis has a growing list of associated parasites (Copp et al. 2009): Parasites in the family Myxobolidae, are known to infect S. glanis and can have a significant pathological impact on wild and cultured fishes. Such episodes of infection are often preceded by environmental stressors such as oxygen depletion (Lom and Dykova 1992). Acanthocephalans (L. plagicephalus), another common parasite of S. glanis, can cause extensive damage such as lesions to the intestinal tract of fish where they attach leading secondarily to infections by bacteria (Dezfuli et al. 1990). High intensities of parasitic crustaceans such as Ergasilus sieboldi can inflict severe damage to the gills (Dezfuli et al. 2003) resulting in large scale mortalities of fish (Kabata 1979). Silurus glanis is also subject to Aeromonas veronii infection, which is known to cause economic losses in aquaculture (Xiucai et al. 2019). The parasitic nematode Anisaki schupakovbia infects S. glanis, which when consumed by humans can cause anisakiasis (Abdybekova et al. 2020). Other known parasites include Triaenophorus crassus, Raphidascaroides sp., Lernaea cyprinacea (Khara et al. 2016), Lamproglena pulchella (Molnar et al. 2018), Sphaerospora siluri (Patra et al. 2018), Thaparocleidus vistulensi (Rees 2020), and mycoplasmas (Sellyei et al. 2020). Silurus glanis can carry the European sheatfish virus (ESV), a strain of ranavirus, which has been reported to also infect and be lethal to Zebrafish (Danio rerio), Pike (Esox lucius), and Pike-perch (Sander lucioperca) (Jensen et al. 2009, 2011; Martin et al. 2015).

Accumulation of heavy metals and chemicals such as PCBs and PAHs in S. glanis has been recorded above acceptable levels for human consumption and may be damaging to ecosystem health (Ivanovic et al. 2016; Milanov et al. 2016; Pastorino et al. 2016; Squadrone et al. 2016).

There is little or no evidence to support that Silurus glanis has the potential for significant socio-economic impacts if introduced to the Great Lakes.

Accumulation of heavy metals and chemicals such as PCBs and PAHs in S. glanis has been recorded above acceptable levels for human consumption and may be damaging to ecosystem health (Ivanovic et al. 2016; Milanov et al. 2016; Pastorino et al. 2016; Squadrone et al. 2016).

The parasitic nematode Anisaki schupakovbia infects S. glanis, which when consumed by humans can cause anisakiasis (Abdybekova et al. 2020).

Silurus glanis has the potential for high beneficial impact if introduced to the Great Lakes.

Silurus glanis has an economic importance in commercial and recreational fisheries as well as in aquaculture. Its aquaculture production has increased from 600 tonnes in 1993 to 2,000 tonnes in 2002 in ten European countries (Linhart et al. 2002; Copp et al. 2009). Fast and efficient growth, ease of breeding and rearing, and recent genome manipulation makes S. glanis ideal for commercial aquaculture (Copp et al. 2009; Cucherousset et al. 2018). Silurus glanis is considered a delicacy in some countries (Hungary, Poland, Slovakia, Lithuania), where it is exploited for its flesh (tender white meat), skin (for leather and glue production), and eggs (for caviar) (Copp et al. 2009). The flesh of S. glanis is highly nutritious in regard to fatty acid composition (Saliu et al. 2017; Linhartova et al. 2018) and protein quality (Pyz-Lukasik and Paszkiewicz 2018).The popularity of S. glanis relates to the large sizes they can reach; they are perceived as an attractive big-game species by many United Kingdom anglers (Hickley and Chare 2004). They are also a prized pet species, with specimens in the United States advertised for thousands of dollars.

The broad diet of S. glanis extends to species considered invasive to the Great Lakes, including Sea Lamprey (Petromyzon marinus) (Boulêtreau et al. 2020), Rudd (Scardinius erythrophthalmus), Tubenose (Proterorhinus semilunaris), Round (Neogobius melanostomus) and Monkey Goby (Neogobius fluviatilis), and Zebra mussels (Dreissena polymorpha) (Didenko et al. 2016; Mikl et al. 2017). They also consume European Perch (Perca fluviatilis) eggs, which were originally thought to be unpalatable to fish (Vejrik et al. 2017b).

Silurus glanis has value as a research and medicinal subject. Its environmental resilience and longevity make it useful for modeling the effects of parasites (Defzuli et al. 2017) and contamination of hexachlorobenzene and hexachlorobutadiene (Dosis et al. 2017). Further, S. glanis is an important model for investigating evolutionary dynamics of fish chromosomes (Ditcharoen et al. 2019).


Management: Regulations (pertaining to the Great Lakes region)

Federally banned in the United States from import and trade under the Lacey Act. In Indiana (312 IAC 9-6-7), Michigan (Part 413 of Act 451), Minnesota (§ 84D.07), and Ohio (OAC 1501:31-19-01) Silurus glanis is prohibited, making it illegal to import, propagate, sell, buy, barter, trade, loan, or release into public or private waters in these states. It is also prohibited in the Canadian province of Manitoba (C.C.S.M. c. W65).

Control

Biological

There are no known biological control methods for this species.

Physical

Hook-lines and angling were an effective method of reducing S. glanis populations to harmless levels in two lakes in the Czech Republic (Vejrík et al. 2019)

Chemical

Shock treatment with saltwater (5% NaCl for 3 minutes) was fatal to some S. glanis larvae (Krasteva et al. 2020).

General piscicides (such as rotenone) may be used for control, but expect significant kill of non-target species.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.


Remarks: The regularly cited, largest caught specimen of S. glanis (5 m long and 306 kg), was recently debunked as a sturgeon instead (Boulestreau and Santoul 2016).


References (click for full reference list)


Other Resources:
Author: Fusaro, A., A. Davidson, K. Alame, M. Gappy, E. Baker, G. Nunez, J. Larson, W. Conard, and A. Bartos


Contributing Agencies:
NOAA GLRI Logo


Revision Date: 6/24/2021


Citation for this information:
Fusaro, A., A. Davidson, K. Alame, M. Gappy, E. Baker, G. Nunez, J. Larson, W. Conard, and A. Bartos, 2024, Silurus glanis (Linnaeus, 1758): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=3651&Potential=Y&Type=2&HUCNumber=, Revision Date: 6/24/2021, Access Date: 2/28/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.