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What is Ontario Doing?

To prevent the further spread and introduction of this unwanted invader in the province, Ontario has regulated Tench as prohibited under the Invasive Species Act. For more information on the Invasive Species Act and Regulations visit


Tench is an invasive fish native to Europe and western Asia. It was introduced across the United States in the late 19th century for use as a food and sport fish. Tench were brought illegally to a Quebec fish farm in 1986 and escaped into the Richelieu River; a tributary of the St. Lawrence River. Given the appearance of the fish, especially in its juvenile state, it could also be introduced through being mistakenly identified as some baitfish species and brought to Ontario as live bait.

Tench prefer lakes and slow-moving waterways with abundant vegetation and muddy bottoms. As a benthic, or bottom-feeding fish, it eats shellfish such as snails as well as insect larvae. Tench can live in water with low levels of oxygen and prefer temperatures from 0°C to 24°C.


In Canada, the Tench is established in the Columbia watershed in British Columbia and the Richelieu River in Quebec. However, recent monitoring has led to captures in the St. Lawrence River near Bainsville, ON and the fish has been observed as far south as Prince Edward County near Belleville, ON. It is well established in the United States, particularly in the Mississippi River watershed.

For an up to date distribution map of Tench in Ontario, visit

Impacts of Tench

Scientists have not studied the effects of Tench on native species in Canada, but their behaviour may affect native species and water quality.


  • Tench compete with native minnows, bullheads, and suckers for food and eat large quantities of snails and insect larvae.
  • By feeding heavily on snails, which graze on algae, Tench may contribute to algal blooms.
  • Aggressive feeding by Tench stirs up sediments, leading to cloudy water.

How to Identify Tench

  • Tench are usually 20 – 25 cm (7.9 – 9.8 in) long, with a deep, but thin, body.
  • The body is dark olive to a pale golden-tan above, with a white to bronze belly and a bright reddish-orange eye.
  • The mouth forms the front tip of the head (known as a “terminal” mouth) and has a single whisker (known as a barbel) hanging from each corner.
  • Fins are dark and rounded, with no spines.
  • Scales are small and embedded in thick skin.

The Tench resembles other native and introduced members of the minnow family, but only the Tench has a deep body with small scales, a single whisker (barbel) at each corner of the mouth, and the noticeably red-orange eyes.

What You Can Do

  • Learn how to identify Tench and how to prevent the spread of this unwanted species.
  • Never buy or use Tench as bait. It is against the law to use Tench as bait.
  • Don’t put any live fish into Ontario lakes, rivers, or streams. Return or donate unwanted aquarium fish to a pet store or local school.
  • If you have any information about the illegal importation, distribution, or sale of Tench, report it immediately to the MNRF at 1-877- 847-7667, toll-free any time.. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).
  • If you’ve seen a Tench 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). Tench. Retrieved from:
This factsheet may be reproduced for non-commercial purposes.

Header photo by Alan Butterworth

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