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Wels Catfish

Silurus glanis
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What is Ontario Doing?

To prevent this unwanted invader from coming into the province, Ontario has regulated Wels Catfish as prohibited under the Invasive Species Act, 2015. For more information on the Invasive Species Act and Regulations, visit


Although Wels Catfish has not been reported in Canada or the United States, it is believed that if it is ever introduced, it will fundamentally alter the food webs in Ontario’s waterbodies. This species is one of the largest freshwater fish species in the world and has been given nicknames, including “The Ebro Monster”, “The European Maneater”, and “Man-eating Catfish”. The fish will use deep holes, dense vegetation, woody debris, tree roots, rocks and/or boulders, as well as hollow riverbanks and submerged hollow structures as resting sites. Wels Catfish exhibit strong habitat preferences even within invaded regions, and can become territorial of a preferred location.


Wels Catfish is native to Eurasia, including the waters of the North, Baltic, Black, Caspian, Aral, and Aegean Sea drainages; an area spanning central and Eastern Europe from Germany and Poland to western and central Asia. The native distribution of this species extends as far north as southern Sweden and as far south as Greece, Turkey, and Iran.

The species has been introduced and established populations throughout much of Europe, largely owing to its popularity as a sport fish. It has been extremely successful in expanding its range southward and westward in the Mediterranean basin and has colonized all watersheds in France as well as the Po River Valley in Italy. Reports of the species being documented in areas such as Tunisia, Algeria, Brazil, and China have also been made.

Wels Catfish is generally a benthic fish, meaning that it is most commonly found near the bottom of a waterbody.. It inhabits a wide range of habitat types, including large rivers, lakes, backwaters, floodplains, irrigated channels, ponds, and even brackish water of coastal areas. Within these waterbody types, it prefers muddy and weedy areas with still or slow running waters.

Impacts of Wels Catfish

Wels Catfish exhibits many characteristics of a successful invasive species:


  • it can inhabit a variety of habitat types across different climates.
  • It can consume a broad range of food items, including native species of fish, amphibians, mammals, and birds, ultimately negatively impacting biodiversity.
  • Although they are slow to reach maturity and only spawn once a year, females produce a very large number of eggs (anywhere from 8,000 to 700,000 eggs per fish), and males aggressively guard the young, which increases reproductive success.
  • Competition with native fish species for food and habitat.
  • Potential transmission of parasites and pathogens such as spring viraemia of carp and European sheatfish virus to native fish populations.
  • Wels Catfish may also pose a risk to humans. While extremely rare, there have been reports of this species attacking humans in the water.

How to Identify Wels Catfish

Wels Catfish is one of the world’s largest freshwater fish species, with individuals often reaching lengths of up to 300 cm (3 m), and weights of up to 150 kg (although typically, Wels Catfish range in size from 1.3 – 1.6 m (4.3 – 5.2 ft) long, and weigh 15 to 20 kg (33 to 44 lb).

Like many other catfish species, the Wels Catfish can be characterized by:


  • A long, mucus-coated, scale-less body and a sideways flattened tail.
  • Triangular-shaped head, accounting for about 20% of its body length.
  • Round and flat snout with widely spaced nostrils.
  • Large mouth with very small, pointed teeth, wide gape, and small eyes.
  • Two large barbels on each side of the mouth on the upper jaw and four shorter ones coming from the lower jaw.
  • Pair of powerful fins just behind the head comprised of one spine and up to 18 soft rays.
  • A large anal (lower) fin composing nearly 60% of the total length of the fish.
  • The tail fin is generally small and round in shape.
  • Generally, dark greenish-black colouration along its back, with a marbled or mottled creamy yellow on the sides, and a grey-white underbelly.
    • Albinism is rare, but known to occur in this species of catfish.

What You Can Do

  • Learn how to identify Wels Catfish and how to prevent the introduction or spread of this unwanted species.
  • Never buy or keep Wels Catfish. It is against the law to keep a Wels Catfish as a pet, use it as bait, or have a live Wels Catfish in your possession.
  • Don’t release any live fish into Ontario lakes or rivers. If you are fishing and incidentally catch a Wels Catfish, you must destroy it. Do not return it to the water.
  • If you have any information about the illegal importation, distribution, or sale of Wels Catfish, report it immediately to the MNRF at 1-877-847-7667, toll-free anytime. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).
  • If you’ve seen a Wels Catfish or another invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711, visit EDDMapS, or search for the ‘Invasive Species in Ontario’ project on to report a sighting.

Resource Files


OFAH/OMNRF Invading Species Awareness Program. (2021). Wels Catfish. Retrieved from:
This factsheet may be reproduced for non-commercial purposes.

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Reporting Invasive Species | Ontario's Invading Species Awareness Program

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