Wels catfish (Silurus glanis)

Synonyms: Silurus glanis Linnaeus

Common Names: Wels, European catfish, sheatfish, Danube catfish

Description:

Wels catfish (Silurus glanis) is a giant freshwater fish from central and eastern Europe and western Asia, and one of the largest freshwater fish in the world [1][2]. It is a nocturnal predator that can grow over 9 feet long and weigh more than 200 pounds, eating fish, crayfish, frogs, and even waterbirds [1][2]. MISIN tracks it because it is not yet established in North America, it is illegal to import under U.S. federal law, and it could badly harm native fish and waterbirds if it were released into our waters [1].

Identification:

Wels catfish is an unmistakably huge, scaleless, slimy fish with a broad, flattened head and a very wide mouth [1]. It has six barbels (the whisker-like feelers around a catfish's mouth): two long ones at the corners of the upper jaw and four shorter ones on the chin [1][3]. Its body is dark greenish-black to brown with a mottled pattern, paler yellowish sides, and a whitish belly [1]. The clearest shape clue is the fins: a very long anal fin runs most of the way along the underside to a rounded tail, while the dorsal fin on the back is tiny [1].

The fish is active mostly at night and lives in the water year-round, so it is rarely seen in the open. Because it is not native here, any sighting matters: a catfish far larger than any native one, with six barbels and a long anal fin, is worth reporting right away [1][3].

At-a-glance cues:

1. Very large, scaleless, slimy catfish ? can exceed 9 feet long and 200 pounds [1][2]
2. Broad, flat head and wide mouth with six barbels, including two long ones at the corners of the mouth [1][3]
3. A very long anal fin running most of the way to a rounded tail, with only a tiny dorsal fin on the back [1]
4. Dark greenish-black to brown, mottled body with pale yellowish sides [1]

Habitat:

Wels catfish lives in large, slow lowland rivers, backwaters, reservoirs, and warm, well-vegetated lakes, and it can tolerate the slightly salty (brackish) water where rivers meet the sea [1][2]. It is a bottom-oriented fish that favors deep, slow, food-rich water [2].

The species is native to central and eastern Europe and western Asia [1]. It is not established in North America, but experts rate it as having a high chance of taking hold if it were introduced, including in the Great Lakes [1]. As a top predator, its "hosts" are really its prey ? native fish, crayfish, frogs, waterbirds, and even small mammals [1][2].

Reproduction:

Wels catfish would almost always reach a new water through people, not on its own. It spreads when someone illegally stocks it or dumps an unwanted aquarium or pond fish into the wild [1]. In fact, it is illegal under U.S. federal law to import wels catfish or move it across state lines, because it is listed as injurious wildlife under the Lacey Act [1][4]. The simplest way to keep it out is to never buy, keep, or release one.

Where it does live, it breeds once a year in spring to early summer, when the water warms to about 64?72 ?F (18?22 ?C) [1]. The male builds and guards a shallow nest in vegetation, and a single female can lay tens of thousands to hundreds of thousands of eggs, which hatch within a few days [1]. The fish mature in about two to four years and can live for decades, so even a few released fish could build a population over time [1].

Impact and Damage:

For anglers and waterfront property owners, the worry is what a giant predator would do to a local fishery. Wels catfish is an apex predator that can eat large numbers of native fish and reshape the fish community of a lake or river [1]. Where it has been introduced outside its native range in Europe, it has reduced fish populations and, at some reservoirs, even lowered the number of waterbirds [1]. It can also carry diseases and parasites that spread to other fish [1].

People are not its prey, but it is not a safe fish to eat from polluted water ? it can carry parasites and build up contaminants in its flesh [1]. For natural area stewards, an established population would compete with and prey on native fish and could disrupt food webs across an entire waterbody, and because the fish grows huge and lives for decades, that damage would be long-lasting [1][2].

Similar species:

Wels catfish can be mistaken for native North American catfish, but two features set it apart: native catfish have eight barbels (four pairs), while wels has only six (with two very long ones), and wels has a very long anal fin leading to a rounded tail and grows far larger than any native catfish [1].

Channel catfish (Ictalurus punctatus) has a deeply forked tail, often dark spots, and eight barbels ? unlike the rounded tail and six barbels of wels [1]. Flathead catfish (Pylodictis olivaris) has a flat head and mottled body like wels, but eight barbels and a much shorter anal fin [1]. Blue catfish (Ictalurus furcatus) also has a forked tail and eight barbels, while wels has a rounded tail and six barbels [1]. Brown bullhead (Ameiurus nebulosus) has a rounded tail but is small, with eight barbels and a short anal fin, whereas wels is enormous with a very long anal fin [1].

Monitoring and rapid response:

Signs to watch for:

1. A catfish far larger than any native one ? feet long and very heavy ? with a broad flat head and wide mouth [1][2]
2. Six barbels (two long ones at the corners of the mouth) and a very long anal fin running to a rounded tail [1]
3. One caught by anglers, or seen in a pond or aquarium, anywhere in North America [1]

What you can do:

1. Never buy, keep, stock, or release wels catfish ? importing it or moving it across state lines is illegal under federal law [1][4].
2. Never release any aquarium or pond fish into the wild; rehome or humanely dispose of unwanted fish instead.
3. If you catch or find one, do not put it back ? keep it, take clear photos, note the exact location, and report it right away (below) [1].
4. Clean, drain, and dry boats, livewells, and gear when moving between waters so you do not move fish or eggs.
5. For natural area crews and agencies, the priority for a species not yet established is rapid response: confirm reports quickly, and where a fish is found, trained fisheries staff use targeted netting or electrofishing to remove it before it can spread, while monitoring high-risk waters [1].

When to call a professional:

1. Any confirmed or suspected wels catfish ? removing a large predatory fish is a job for your fisheries or natural resources agency.
2. Any waterbody where one has been caught more than once, which may signal an establishing population.
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Silurus glanis (Wels Catfish) ? Great Lakes Species Profile (summarizes Copp et al. 2009, Carol et al. 2009, and Vejrik et al. 2017). nas.er.usgs.gov
2. CABI Compendium. Silurus glanis (wels catfish). semanticscholar.org
3. Michigan Department of Natural Resources. Invasive Species: Wels Catfish (Silurus glanis). michigan.gov/invasives
4. U.S. Fish & Wildlife Service. Wels Catfish (Silurus glanis) ? Ecological Risk Screening Summary / Injurious Wildlife (Lacey Act). fws.gov

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