Silurus glanis (wels catfish)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Causes
- Impact Summary
- Economic Impact
- Environmental Impact
- Threatened Species
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Silurus glanis Linnaeus, 1758
Preferred Common Name
- wels catfish
Other Scientific Names
- Siluris glanis Linnaeus, 1758
- Silurus glanis aralensis Kessler, 1872
- Silurus silurus Wulff, 1765
International Common Names
- English: Danube catfish; Danubian wels; European catfish; sheatfish; som catfish; wels
- Spanish: siluro
- French: silure glane
- Russian: obyknovennyi; obyknovennyi som; som
Local Common Names
- Albania: peshku mace europian; siluri
- Austria: Waller; Wels
- Azerbaijan: som
- Bulgaria: som
- Czech Republic: sumec; sumec obecny; sumec velký
- Denmark: malle
- Estonia: säga; wels
- Finland: monni; säkiä
- Germany: Europäischer Flußwels; Uwelra; Waller; Weller; Welro; Wels; Wils; Wilß
- Greece: glanidi; goulianos
- Hungary: harcsa
- Iran: esbele; esbele Europaiye; esbeleh; gorba-mahi; mahi-e Sebili; nake
- Italy: siluro
- Kazakhstan: wels
- Latvia: sams; som
- Lithuania: šamas
- Netherlands: meerval
- Norway: malle
- Poland: sum; sum pospolity
- Portugal: siluro-europeu
- Romania: iaprac; iarma; moaca; somn; somn-pana; somotei
- Serbia: som
- Slovakia: sumec obycajný
- Slovenia: som
- Sweden: mal
- Switzerland: siluro; waller
- Turkey: yayin baligi
- Ukraine: rechnoi som
- Uzbekistan: wels
- Yugoslavia (Serbia and Montenegro): som
Summary of InvasivenessTop of page
S. glanis is the largest-bodied European freshwater fish. Native to eastern Europe and western Asia it is now established in several countries to the west and south of its native range. The risks to native species are through disease and parasite transmission, competition for benthic habitats and predation. In an initial invasiveness assessment, Copp et al. (2005) gave S. glanis an intermediate mean risk score (21.5 out of 54 possible points). However, many aspects of behaviour are still unknown, and Valadou (2007) suggests that virtually all aspects of the biology of introduced S. glanis require study.
In Spain, wels catfish have become a dominant predatory fish in the Ebro river basins, where establishment is likely to have been aided by the relatively warm water temperatures experienced in the region. Establishment may be more sporadic in northern countries such as Belgium and the UK where temperatures are less favourable (Elvira, 2001; Britton and Pegg, 2007). Consumption of food sources is related to gape size with the larger catfish >120 cm in length consuming aquatic wildfowl and mammals in comparison to smaller counterparts of <30 cm feeding on invertebrates and molluscs.
Gozlan et al. (2003) reported that more than 50% of successful invasive fish species introduced into the UK exhibit parental care, where fish actively protect and guard their eggs or larvae and defend territories. Wels catfish exhibit parental care of young, and the males guard clusters of eggs adhered to woody tree roots and submerged macrophytes in riparian reaches and floodplains (Copp et al., 2009).
Invasiveness of non-native fish species may be related to frequent repetitive introductions through anthropogenic pathways. Introduction of S. glanis for aquaculture and enhancement of sport angling is common. Proliferation has been assisted by unregulated introductions in many countries (Hickley and Chare, 2004; Clavero and Garcia-Berthou, 2006). Deliberate introductions have also been followed by accidental escape and dispersal to other waters, as has been reported by Boeseman (1975) in the Netherlands, where it was introduced from Hungary.
S. glanis is listed as Least Concern (LC) in the IUCN Red List of Threatened Species (http://www.iucnredlist.org/). In parts of its native range (e.g. Sweden and Greece) it is under threat from climate and habitat changes and species introductions (Copp et al., 2009; Britton et al., 2010).
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Chordata
- Subphylum: Vertebrata
- Class: Actinopterygii
- Order: Siluriformes
- Family: Siluridae
- Genus: Silurus
- Species: Silurus glanis
Notes on Taxonomy and NomenclatureTop of page
The wels catfish S. glanis is part of the family Siluridae, a group of freshwater fish native to Europe, Asia and Africa. There are 100 species from 12 genera in the family. There are 18 Silurus species, of which two are native to Europe: wels catfish and Aristotle's catfish (S. aristotelis). Wels catfish is the largest fish of the order Siluriformes and can attain a maximum length of 500 cm, although it more commonly reaches 300 cm. It is the largest-bodied European freshwater fish (Copp et al., 2009).
DescriptionTop of page
Wels catfish are distinguishable by an elongated scale-less, slime-covered body, with strong upper body strength and laterally flattened tail. They have a tiny dorsal fin made up of a single spine and 4-5 dorsal soft rays, one anal spine, 83-95 soft anal rays and a caudal fin of 17 soft rays (Froese and Pauly, 2012). Their paired pelvic fins are each made up of one spine and 11-12 soft rays and have paired pectoral fins of one spine and 14-17 soft rays. They can be identified by 6 barbels, 2 long ones on each side of the mouth and 4 shorter ones from the lower jaw. Their eyes are small and they rely on their barbels and olfactory cavities to sense their prey and environment rather than vision. They are a demersal species, find refuge in crevices and woody root habitats, and prefer slow flowing rivers and weedy covered, vegetated lakes. Body colour is variable but normally dark greenish-black with creamy yellow sides creating a mottled effect.They are solitary, predatory, opportunistic scavengers that hunt for stragglers (Boujard, 1995; Copp et al., 2009; Britton et al., 2010).
Maximum length is 500 cm (male), but common lengths are 300 cm, and weight 306 kg. Maximum reported age is 80 yrs (Kottelat and Freyhof, 2007), although life span is commonly 15-30 yrs. Length at first maturity is 39-71 cm. Age at maturity is 3-4 yrs. Males mature earlier than females, with mass maturation at 3-4 yrs, 57-66 cm and 1.3-2.3 kg, in contrast to females that mature at 4 yrs at minimum length 87.05 cm (Alp et al., 2004; Froese and Pauly, 2012). In adults, the gonads are 9-15% of total body weight. Testicles in males are a pair of glands in the dorsal main cavity, white when mature, but pink when developing (Shikhshabekov, 1978). Males have running milt 30-40 days before spawning and produce sperm for relatively long periods, with a gradual, extended duration of spermatozoa discharge (Shikhshabekov, 1978). Ovaries are in caudal posterior cavity in females, on maturity they expand into abdominal cavity, and are small in size. Each gram of ova has about 195 eggs prior to spawning. The eggs are large, about 1-3 mm in diameter (Copp et al., 2009).
DistributionTop of page
S. glanis is native to eastern Europe and western Asia (Kinzelbach, 1992), but is now established in at least seven countries to the west and south of its native range (Elvira, 2001). Migration to European rivers including the Danube, Dnieper and Volga was via the Caspian, Black and Aral seas. Native populations extend from Germany to Eastern Europe including Poland and southern Sweden, and also from northern Iran and southern Turkey to the Baltic states and Russia, and to the Aral sea of Kazakhstan and Uzbekistan (Copp et al., 2009).
Following introduction outside its native range, the wels catfish has become established in Bosnia-Herzegovina, Spain, Denmark and Tunisia with some ecological effects. It is also established in Italy, Syria, Portugal, Croatia, Turkey, the UK, France, the Netherlands and China, although ecological impact here is unknown. It has been introduced but not established in Cyprus, Belgium and Algeria (Froese and Pauly, 2012).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
History of Introduction and SpreadTop of page
S. glanis was introduced to the UK and western Europe in the nineteenth century. It was first introduced to England in 1880, into enclosed recreational lakes of a private Bedfordshire manor estate at Woburn Abbey, for fishing. Currently, wels catfish are predominantly found in the South East and Midlands areas of the UK. The species was later introduced to Spain in the twentieth century and reintroduced to Belgium, Netherlands and France. It was introduced for angling and aquaculture in Spain, Italy and France. Simoens et al. (2002) report that in Lake Schulen in Flanders (Belgium), large wels catfish which had been illegally introduced by anglers had successfully reproduced. Introductions to rivers in Spain have resulted in abundant populations in four river basins, where catfish can reach large sizes > 1 m (Carol et al., 2009). Another reason for introductions is as a biocontrol agent for controlling cyprinid fish. S. glanis was introduced to Netherlands from Hungary for this purpose.
According to Linhart et al. (2002), S. glanis has been farmed historically in Austria, Bulgaria, Croatia, Germany, France, Hungary, Greece, Macedonia, Poland, the Czech Republic and Romania. Since 1975, it has been farmed for its meat in pond cultures in Italy and former Yugoslavia, and also in its native range in Hungary, Poland, Slovakia and Lithuania (and also Belarus -- Dokuchayeva, 2011), where the species is considered an expensive meat delicacy. Its greater production in Bulgaria has been suggested (Hadjinikolova et al., 2010). The skin can be used in glue and leather manufacture. However the species still accounts for only a small percentage of European freshwater aquaculture.
IntroductionsTop of page
|Introduced to||Introduced from||Year||Reason||Introduced by||Established in wild through||References||Notes|
|Natural reproduction||Continuous restocking|
|Algeria||Hungary||1985||No||No||Froese and Pauly (2012)|
|Belgium||1983||No||No||Froese and Pauly (2012)|
|China||France||1990||Yes||No||Froese and Pauly (2012)|
|China||Hungary||1990||Yes||No||Froese and Pauly (2012)|
|Cyprus||Yugoslavia (former)||1979||No||No||Froese and Pauly (2012)|
|Denmark||Sweden||1881||Yes||No||Froese and Pauly (2012)|
|Denmark||Germany||1881||Yes||No||Froese and Pauly (2012)|
|France||Central Europe||1857||Yes||No||Froese and Pauly (2012)|
|Germany||Eastern Europe||1853||No||No||Froese and Pauly (2012)|
|Italy||Yugoslavia (former)||1900-1924||Yes||No||Froese and Pauly (2012)|
|Netherlands||Hungary||1970||Yes||No||Froese and Pauly (2012)|
|Spain||Germany||1980||Yes||No||Froese and Pauly (2012)|
|Tunisia||Germany||1990||Yes||No||Froese and Pauly (2012)|
|UK||Germany||1880||Yes||No||Froese and Pauly (2012)|
Risk of IntroductionTop of page
The routes used to introduce non-native fish species are closely related to the nature and extent of different anthropogenic activities such as aquaculture, research, pest control and also recreational fishing. According to Naylor et al. (2001), aquaculture is the foremost transfer route of exotic fish species globally, which reflects the growth in aquaculture caused by the increasing demand for fish consumption which cannot be provided by wild fish capture alone.
Routes of introduction of S. glanis include recreational angling, aquaculture and also use as a biological control agent for cyprinid fish, with certain pathways being more frequent in some countries; for example, the species is predominantly farmed in aquaculture in Italy, Romania, Poland and the Netherlands, but used mainly to enhance recreational angling in the UK. Aquaculture of this species is constrained by water temperatures <10ºC during winter months in some regions of Europe including France. Risk of establishment increases in warmer climates such as the Mediterranean as rapid growth and breeding are enhanced by warmer temperatures of 25-28ºC in contrast to likelihood of more sporadic establishment in Northern climates.
The different routes of introduction are pertinent regarding release of non-native fish, as some routes such as angling have a greater risk of unregulated transfer activities from fishermen in unsupervised lakes. Some angling introductions are unregulated and illegal, with S. glanis transferred to unlicensed lakes in the UK that do not meet the ILFA (Import of Live Fish Act) criteria set by the Environment Agency because of risks concerning flooding and the likelihood of entry to nearby rivers. Consent is usually not granted for open waters, although enclosed waters are permitted (Britton and Pegg, 2007; Copp et al., 2009). In April 2012, accidental flooding from licensed lakes containing wels catfish into flood valleys of the River Colne and Chelmer in East Anglia were being investigated. S. glanis is cited as present in some rivers in the UK, e.g. River Thames, River Great Ouse, where its presence is yet to be proved (Copp et al., 2007).
This species is in the lower region of the high risk score category of potential pests in ENSAR (European non-native species aquaculture risk assessment) to evaluate the risk of introduction, establishment, dispersal and impacts, although this may be variable according to context (Copp et al., 2009).
HabitatTop of page
Preferred habitats are slow flowing lowland rivers, backwaters, shallow channels in floodplains and weed covered lakes. Within these habitats the fish prefer benthic woody tree root habitats and stony crevices for refuge and cover. They can also use holes or burrows of clay and muddy bottom substrate of lakes and ponds and are often hidden among dense macrophyte cover. Larvae and juveniles are benthic feeders of invertebrate zooplankton such as Rotatoria, Copepoda and Cladocera. In their native range, catfish are under threat from anthropogenic changes including river modifications resulting in the loss of shallow spawning sites (Hamackova et al., 1997; Copp et al., 2005; Copp et al., 2007). The species sometimes enters brackish water in the Black Sea and Baltic Sea (Froese and Pauly, 2012).
Habitat ListTop of page
|Irrigation channels||Present, no further details||Natural|
|Lakes||Present, no further details||Natural|
|Reservoirs||Present, no further details||Productive/non-natural|
|Rivers / streams||Present, no further details||Natural|
|Ponds||Present, no further details||Natural|
|Ponds||Present, no further details||Productive/non-natural|
|Estuaries||Present, no further details||Natural|
|Lagoons||Present, no further details||Natural|
Biology and EcologyTop of page
Although the genetic structure and phylogeography have been studied in its native range, there is little information known about the genetic characteristics of S. glanis in its introduced range (Copp et al., 2009). Information regarding the wels catfish nuclear and mitochondrial genomes is sparse. The mitochondrial genome has 16,526 base pairs containing 37 genes, of which 13 genes are for protein synthesis, 22 tRNAs and 2rRNAs, and a control region which functions in the same way as other vertebrate mtDNAs. From phylogenetic analysis it seems likely that wels catfish represent an early diversification of Siluriformes (Vittas et al., 2011). S. glanis has fewer alleles than S. aristotelis and S. triostegus but similar observed and expected heterozygosities (Krieg et al., 1999).
To protect species or infer their invasiveness potential, it is necessary to understand the origin, genetic diversity and migration patterns. Triantafyllidis et al. (2002) investigated the genetic structure of S. glanis across most of its natural distribution using 10 microsatellite loci. The revealed that levels of genetic diversity were much higher than previous allozyme and restriction fragment length polymorphism mitochondrial DNA analyses had shown. Despite the great genetic differentiation of S. glanis populations, no consistent pattern of geographical structuring was revealed, in contrast to previous studies of European freshwater fish species. A model of isolation by distance seems more probable and a hypothesis of recent dispersion from only one glacial refugium around the Ponto-Caspian region is proposed.
Reproduction is controlled by environmental cues, e.g. temperature and day length. Upstream spring migration in April for spawning requires temperatures of 8-10ºC and initiation of spawning occurs at 18-22ºC. There is one clear seasonal peak in spawning per year, between May and July. Spawning is nocturnal.
Pairing up of males and females commences during migration as they proceed to compete for best spawning grounds in the reach of the river and in heavily vegetated lakes. Sexual maturity is generally 3-4 yrs, between 39-71 cm length.
Following spawning, S. glanis exhibits a guarders and nesters reproductive strategy with the male protecting the cluster of eggs laid by the female in his nest excavated amongst the substratum and made from plant material. Females deposit eggs at 30,000 per kg of body weight. The male guards the eggs for the next 2-10 days (time dependent on water temperature) and makes sure the eggs are well ventilated by repeatedly fanning his tail fin, until they hatch out (Copp et al., 2009).
The larvae live in the nest until the yolk sac is absorbed. Eggs are protected by mucous and stickiness. Incubation lasts about 50 hours at 24°C. Egg size is 3 mm and larvae length at hatching is 8.5 mm. The young grow quickly, reaching 30 cm in length within the first year (Shikhshabekov, 1978; Copp et al., 2009).
Physiology and Phenology
The anatomy and location of fins and body shape of S. glanis indicate that this fish is a demersal species, with a powerful pair of pectoral fins that is positioned behind the gills at the base of the ventral fins, small pelvic fins situated by the anal vent and an elongated anal fin that is over 50% of its body length. The tiny dorsal fin on its upper body, rounded caudal fin and strong upper body assist the swimming motion. The species is an effective ambush predator of slower moving Cyprinid species (Copp et al., 2009).
The flattened snout with spaced apart nostrils and long barbels on either side of the upper jaw, and 4 shorter barbels on the lower jaw, indicate that S. glanis sense their prey by highly sensitive chemical and olfactory sensors on their barbels and nostrils rather than by vision, as their eyes are small; this can be related to their benthic habitat ecology (Copp et al., 2009).
S. glanis is a robust species regarding transference outside its native range, and exhibits tolerance to low oxygen levels in water.
Life span is normally 15-30 years, with a maximum recorded age of 80 years (Kottelat and Freyhof, 2007).
Habitat use follows a daily pattern, and incorporates territorial behaviour. Activity peaks during the night, with nocturnal foraging motivated by hunger stimuli. There is intensive daytime use of littoral habitat, resting within dense vegetation (Copp et al., 2009).
S. glanis has a broad omnivorous diet, including invertebrates and vertebrates such as small rodents. Diet varies with age and size, with smaller catfish foraging on invertebrates, while larger catfish >120 cm are able to exploit a broader niche, including fish and wildfowl. The diet of small juveniles is sometimes almost entirely invertebrates, but can also be composed of benthic or mid-water column organisms such as Chironomidae, and during their first year S. glanis take an increasing proportion of young-of-the-year (YoY) fish. Copepoda are the most frequent food of smaller larvae.
The diet of adult fish is known to include sunbleak (Leucaspius delineatus), ruffe (Gymnocephalus cernuus), roach (Rutilus rutilus), dace (Leuciscus leuciscus), common bream (Abramis brama), silver bream (Blicca bjoerkna), rudd (Scardinus erythrophthalmus), bitterling (Rhodeus sericeus), European eel (Anguilla anguilla), red swamp crayfish (Procambarus clarkii) and signal crayfish (Pacifastacus leniusculus). Copp et al. (2009) present a table of at least 55 fish species found in the natural diet of S. glanis.
Most research on the environmental requirements of S. glanis has been focussed on introduced ranges in western Europe rather than northern habitats, as warmer water temperatures cause more serious ecological impacts, for example rapid growth (Boulêtreau et al. 2011; Syväranta et al. 2010), predation and trophic impact (Czarnecki et al. 2003; Carol et al. 2007; Carol et al. 2009; Copp et al. 2009; Syväranta et al. 2009Bevacqua et al. 2011; Martino et al. 2011; Cucherousset et al. 2012).
This species requires temperatures of 25-28ºC for optimal growth, food assimilation and breeding (Copp et al., 2009). However, there are reports of breeding in some lakes in southern England at present temperatures (Copp et al., 2009). Establishment success in France has been restricted by cold winter temperatures of <10ºC (David, 2006). The predicted increase of water temperatures of 2-3ºC by 2050 as a result of climate change is likely to amplify the risk of establishment and breeding success in the UK and other northern countries (Rahel and Olden, 2008; Britton et al., 2010).
Fast growth is advantageous for non-natives in minimising predation by quickly exceeding gape size of native predators, and in increasing foraging opportunities (Hendry et al. 2000). Larval and juvenile stages of introduced fish are most susceptible to predation due to small size (Gozlan et al. 2003), and also overwintering mortality as S. glanis larvae are unable to survive low temperatures <13ºC (David, 2006; Copp et al. 2009). Previous studies of cultured S. glanis in central and eastern Europe indicated that this species is capable of rapid growth in warm waters >20ºC (Linhart et al. 2002; Ulikowski et al. 2003Gullu et al. 2008; Muscalu et al. 2010), and spawning behaviour was also temperature sensitive -- spawning was delayed for months until water temperatures were within the 18-23ºC range (Wiśniewolski, 1989; Copp et al. 2009). Growth is an integrating variable of fish physiology and behaviour, and reduced growth can result from a variety of factors: food abundance, fish age, social hierarchy, change in water temperature, habitat and increased energy expenditures (Zaikov et al. 2008). There is considerable research on growth of S. glanis in aquaculture (Harka, 1984; Hilge, 1984, 1985; Mareš et al. 1996; Ulikowski et al. 1998; Zaykov and Hubenova-Siderova, 1998; Prokés et al., 1999; Grozev et al., 2000; Bogut et al., 2002; Paschos et al., 2004; Kim et al., 2005; Dediu et al., 2010; Alp et al., 2011; Jamróz et al., 2008; Muscalu et al., 2010), and on food conversion of cultured S. glanis (particularly using meal pellets), e.g. (Hamáčková et al., 1993; Bogut et al., 1995; Filipiak et al., 1997; Mareš et al., 2003), but there is little data available about growth using forage fish as food in natural ponds (Zaikov et al., 2008; Cirkovic, 2012). S. glanis is a warm water predatory fish with fast growth rate (Cirkovic, 2012); cultured fish can attain a mean length increment of >15cm TL within 4 months at optimum temperatures >26ºC (Hilge, 1989). Several studies have indicated that the temperature threshold for optimum growth may vary between 22 and 26ºC (Mazurkiewicz et al., 2008), or 23-30ºC (Ulikowski et al., 2003) whereas Copp et al. (2009) indicated a narrower range between 25 and 28ºC.
Overall, the tipping point temperature indicator for growth among cultured S. glanis appeared to be >20ºC and at these temperatures fish can gain ~ 4kg within 2yrs, in contrast to depressed growth at lower temperatures (Gullu et al. 2008). Foraging is an important aspect of growth and Muscalu et al. (2010) revealed that water temperatures <17ºC marked a cessation in foraging activity and growth, which indicates thermal ecological sensitivity of S. glanis of particular relevance in northern habitats. Other examples of depressed foraging activity and growth were reported at water temperatures <15ºC as fish were unable to metabolise food at temperatures <10ºC and were sedentary to minimise energy expenditure (Boujard, 1995).
ClimateTop of page
|C - Temperate/Mesothermal climate||Preferred||Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C|
|Cf - Warm temperate climate, wet all year||Preferred||Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year|
|Cs - Warm temperate climate with dry summer||Preferred||Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers|
|Cw - Warm temperate climate with dry winter||Preferred||Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)|
Natural enemiesTop of page
Notes on Natural EnemiesTop of page
Natural predators of S. glanis include otters (Lutra lutra), cormorants and waders, and other predatory fish such as pike (Esox lucius) and zander (Sander lucioperca). S. glanis exhibits cannibalism when food resources are scarce, or (Copp et al., 2009) in angling waters when there is variation in size among members of the species.
Means of Movement and DispersalTop of page
Movement to new areas is generally through introduction for aquaculture and recreational fishing, or sometimes for biological control. S. glanis is robust enough during transport (even in minimal water and over considerable distances) to be translocated to areas outside its native geographical range (Copp et al., 2009). There are reports of escapes from aquaculture and recreational fisheries, for example in France where it escaped into the River Doubs in about 1890 (Valadou, 2007).
It appears to establish relatively easily after introduction, especially in warmer climates such as around the Mediterranean (Crivelli, 1995). The large size suggests high potential for dispersal (Copp et al., 2009), although the limited available information on movement and migration suggests that the species demonstrates considerable site fidelity (Carol et al., 2007). There is potential for dispersal during hydrological events (Slavik et al., 2007). Penil (2004) suggests that it may expand its range by movement in man-made canal networks. Copp et al. (2009) say that it is most common in the River Ebro, Spain, in the 130 km between its point of introduction in 1974 and the Ebro delta, and suggest that natural dispersal is likely to be slow and density dependent.
Concerns about accidental unregulated spread (flooding enabling spread from angling waters to watercourses and rivers) and intentional unregulated releases (for angling) imply that S. glanis introductions need to be investigated, particularly as angling and dispersal are cited as the main introduction routes for introduced fish in the UK ( Copp et al. 2009; Rees, 2010; Hickley and Chare, 2004). In the UK, wels catfish, because they are non-native, require an ILFA (Introduction of Live Fish Act) license for introduction as part of regulatory legislation control and enforcement.
Pathway CausesTop of page
Impact SummaryTop of page
|Environment (generally)||Positive and negative|
Economic ImpactTop of page
The addition of wels catfish in recreational catch and release fisheries is likely to have a beneficial revenue effect. However, consideration must be given to the economic costs that are likely to arise from management control policies with the removal of S. glanis from unlicensed waters; monitoring, removal costs and challenges in recapturing demersal species. Removal of wels catfish from unlicensed lakes appears to be a priority for the Environment Agency in England and Wales, although how successful these measures are in practice has yet to be ascertained.
Some of the environmental impacts of the species (see the Environmental Impact section) might have economic effects.
For positive economic effects, see the sections on Uses (Invasive Species Compendium) or Production, Economic and Socioeconomic Aspects (Aquaculture Compendium).
Environmental ImpactTop of page
There is a risk that wels catfish may impact on native fauna for a number of reasons. Firstly they may increase competition for habitats of native fish, including the critically endangered eel (Anguilla anguilla). However, Martino et al. (2011) reported that in the Camargue in Southern France, S. glanis consumption was not a threat to eel distribution, as their diet was mainly omnivorous. Secondly, catfish are opportunistic foragers, able to switch their feeding to the most suitable resource available.
The ecological trophic effect of S. glanis is unclear; some authors consider that the species can decimate tench (Tinca tinca) populations while others are of the view that as they are to some extent scavengers, their predatory impact may be benign rather than intense (Copp et al., 2009).
A potential beneficial ecological effect is that S. glanis can predate on signal crayfish (Pacifastacus leniusculus), which is an invasive species in Europe that is adversely effecting native crayfish populations (Carol et al., 2009; Copp et al., 2009).
Wels catfish are carriers of viral pathogens, namely spring viraemia of carp (SVC) and European sheatfish virus (ESV), which may adversely impact native fish including salmonids and amphibians. Wels catfish are also hosts of specialist parasites such as Trichodina siluri, Myxobolus miyarii, Leptorhynchoides plagicephalus and Pseudotracheliastes stellifer which may be detrimental to native fish survival (Copp et al. 2009; Copp et al. 2010).
The potential risk of hybridization with native species is likely to be limited to native Silurus species, such as the native congener S. aristotelis in Greece.
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Anguilla anguilla (European eel)||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered)||Competition - monopolizing resources; Predation||Martino et al., 2011|
|Acipenser naccarii (adriatic sturgeon)||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); USA ESA listing as endangered species USA ESA listing as endangered species||Competition (unspecified); Predation||National Marine Fisheries Service, 2013|
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Has a broad native range
- Highly adaptable to different environments
- Tolerant of shade
- Capable of securing and ingesting a wide range of food
- Long lived
- Fast growing
- Altered trophic level
- Ecosystem change/ habitat alteration
- Modification of natural benthic communities
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Pest and disease transmission
- Rapid growth
- Highly likely to be transported internationally accidentally
- Highly likely to be transported internationally deliberately
- Highly likely to be transported internationally illegally
- Difficult to identify/detect in the field
- Difficult/costly to control
UsesTop of page
S. glanis is a popular fish among anglers because of its large size and relatively frequent capture. The introduction of S. glanis in angling clubs is likely to increase revenue to local communities and generate business. The species is popular with anglers, and a minority of anglers are in favour of releasing it into to rivers, while others are content that it remains in licensed lakes. The sheer size of this fish has also attracted scuba-divers to some lakes where it has been introduced in the Netherlands (and probably elsewhere), which also generates local revenue.
S. glanis is also used in parts of Europe for aquaculture. Fish are filleted and the flesh is cut into steaks or smoked for human consumption. The skin can be used in glue and leather manufacture. According to Linhart et al. (2002), S. glanis has been farmed historically in Austria, Bulgaria, Croatia, Germany, France, Hungary, Greece, Macedonia, Poland, the Czech Republic and Romania. Since 1975, it has been farmed for its meat in pond cultures in Italy and former Yugoslavia, and also in its native range in Hungary, Poland, Slovakia and Lithuania (and also Belarus -- Dokuchayeva, 2011) where it is considered an expensive meat delicacy. Its greater production in Bulgaria has been suggested (Hadjinikolova et al., 2010). However it still accounts for only a small percentage of European freshwater aquaculture compared with the main species, rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta) and common carp (Cyprinus carpio) -- total production of S. glanis was 602 tonnes in 1993, increasing to 2000 tonnes in 2002, and has since stabilised at >700 tonnes/year. In contrast, O. mykiss total production was 300,000 tonnes in 2005, and the figure had risen to 700,000 tonnes in 2010 and was likely to increase (FAO, 2012; Linhart et al. 2002; Varadi et al. 2001).
Consumer popularity of cultured S. glanis has remained low (Varadi et al. 2001) with some limited but renewed awareness among fish farmers in France and Germany (Linhart et al. 2002; Muscalu et al. 2010). Fish consumption is low in central and eastern European countries in comparison to western Europe, which may be related to economic factors including income, fisheries trading and distribution (fish is more expensive than meat in most eastern European countries). Consequently, most fish production is exported to other countries; for example the majority of O. mykiss production in Poland is exported to Germany (FAO, 2012; Varadi et al. 2001).
S. glanis cultivation has played a minor role in cyprinid pond farming. It and Sander lucioperca are predatory fish that are traditionally reared to control wild forage fish dispersed during seasonal pond flooding that may be interspecific competitors with cyprinids (Bokor et al. 2012).
Uses ListTop of page
- Biological control
- Sport (hunting, shooting, fishing, racing)
Human food and beverage
- Meat/fat/offal/blood/bone (whole, cut, fresh, frozen, canned, cured, processed or smoked)
Similarities to Other Species/ConditionsTop of page
Wels catfish can be distinguished from other European catfish by the 6 long barbels under the lower jaw, the scaleless mucous-coated elongated body and the very small dorsal fin (Britton et al., 2010).
Prevention and ControlTop of page
Information on specific control measures for S. glanis is limited. The aim of control management plans in fisheries in reference to non-natives is to develop a framework to assess the risk in relation to priority and action. In the UK, the government has developed an environmental risk strategy including risk identification, risk assessment, risk management and risk review and reporting. The Import of Live Fish Act 1980 (ILFA) is a legislative framework to control importation of non-native fishes, and the Fish Invasive Screening Kit (FISK) is a scoring system to assess the range of risk of non-native fish introduction ranging from potential pest to harmless, based on the evaluation of life history traits of non-native fish species, e.g. size, growth rate, survival rate, and reproductive success. S. glanis is in the lower range of the high risk score of FISK, although these scores are variable and likely to change in relation to the context of environmental factors affecting risk (Copp et al., 2005).
Control management options for S. glanis vary according to assessment of severity of risk. A “do nothing” approach is advocated in low risk situations, whereas removal or containment are considered options in higher risk situations. Options including draining of lakes, application of rotenone, capture of fish by fyke and seine netting, and electrofishing should be all reviewed in control management and risk assessment plans (Britton et al., 2009).
ReferencesTop of page
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ContributorsTop of page
17/12/2013: Updated by:
Ann Rees (address as below)
26/6/2012 Original text by:
Ann Rees, Environment Agency, Rivers House, Shaftsbury Rd, Sunrise Business Est, Blandford, Dorset DT118ST, UK.
Reviewers' names are available on request.
Distribution MapsTop of page
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