Background

Tench is an invasive fish native to Europe and western Asia. It was introduced across the United States in the late 19thcentury for use as a food and sport fish. Tench were brought to a Quebec fish farm illegally in 1986 and escaped into the Richelieu River, a tributary of the St. Lawrence River. The fish could enter Ontario waters if it spreads to the St. Lawrence, or it could spread from the Mississippi River watershed through the Great Lakes. It could also be mistaken for some baitfish species and brought to Ontario as live bait.

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

Range

Tench are not yet known to be in Ontario. In Canada the fish is found only in the Columbia watershed in British Columbia and the Richelieu River in Quebec. It is well established in the United States, particularly in the Mississippi River watershed.

Impacts

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 to 25 centimetres long, with a deep, but thin, body.
  • The body is dark olive to 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, and a single whisker (barbel) at each corner of the mouth.

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 Ministry of Natural Resources TIPS line at 1-877-TIPS-MNR (847-7667) toll-free any time, or contact your local Ministry of Natural Resources and Forestry office during regular business hours. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).
  • If you’ve seen a tench or other invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711, or visit EDDMapS Ontario to report a sighting.

Gallery


OFAH/OMNRF Invading Species Awareness Program. (2012). Tench. Retrieved from: www.invadingspecies.com.
This factsheet may be reproduced for non-commercial purposes.

Header photo by Alan Butterworth