Tench - Columbia Shuswap Invasive Species Society

TENCH (Tinka tinka)

FOUND IN B.C.? Yes.

CURRENTLY KNOWN IN: The Columbia watershed and Okanagan region.

Identification

Tench are large fish that are part of the minnow and carp family. They are 20-84 centimetres long, with small scales that fade from dark green at the single dorsal fin to light yellow at the belly. Their round fins are darker than their body, and they have a flat tail. Tench have a distinct dark orange iris. They are similar in appearance to other carp and minnow fish, but are the only ones to have a single barbell (whisker-like projection) at the corners of the mouth. Tench have been artificially bred to look like Goldfish, and may be stocked as aquarium fish. In this case, Tench appear gold to red in colour and have black or red spots.

Photo credit: Mike Guerin, TheJump.Net, Bugwood.org Via ISCBC

Life Cycle

Tench populations can grow quickly, as females spawn multiple times throughout the summer months, when temperatures reach 18℃, but can reproduce in temperatures as low as 10-16℃! Female Tench produce 300,000-900,000 eggs during a spawning season, and can release hundreds of thousands of eggs per kilogram of body weight. Tench spawn in areas with aquatic vegetation and shallow water. These fish can live up to 20 years.

Photo credit: Ontario’s Invading Species Awareness Program

Ecology

Tench are omnivores, and can tolerate low temperatures and oxygen levels, making them very adaptable to a wide range of habitats. They prefer calm, shallow water with abundant vegetation and a muddy bottom, such as ponds, lakes, and large rivers. Tench can survive in water temperatures between 0-24℃. These fish are mostly active at night, and spend the day under aquatic plants or buried under the mud at the bottom of the water body. During the winter, Tench bury themselves under the mud to survive the cold. These fish can survive low oxygen conditions, and long periods out of water. Due to their small scales and protective mucus layer covering their bodies, Tench are resistant to disease.

Introduction and Spread

Tench are native to Europe and Asia, and were introduced to the United States as sport fish in the 19th century. In 1986, Tench were illegally transported to Quebec where they escaped and spread to the St. Lawrence River. These fish have spread to BC from Washington through the Columbia River.

Photo credit: Sunci Alvlijas

Impacts

Tench are omnivores that feed on aquatic plants, snails, and insect larvae. Through their aggressive feeding behaviour, they out compete native species for food and habitat, and decrease water clarity, preventing aquatic plants from growing. Tench disrupt natural food webs in environments where they are introduced, threatening native species such as minnows, bullheads, and suckers, and reducing biodiversity. They have the potential to compete with other bottom dwelling native fish, and could cause a reduction in invertebrate populations. Tench can also cause algae blooms, as a result of their feeding on snails, who graze on algae. These fish are resistant to disease but are known carriers of parasites that are transmitted to other freshwater fish. Due to these environmental impacts, Tench also cause economic losses to commercial and recreational fishing, and decrease the value of recreation sites such as beaches and parks.

What Can We Do?

To help stop the spread of this invasive species, do not possess, breed, release, sell, or transport Tench. Using live finfish as bait is prohibited in BC, and juvenile Tench can be confused as bait fish and accidentally spread in the release of bait buckets. Be aware of the aquarium fish you are purchasing, and make sure it is not a prohibited species. If you have aquarium fish or any other pets you can no longer care for, Don’t Let it Loose, as they can become invasive in the environment in which they are released!

REPORT: Report all sightings of invasive species to CSISS on our website, to the Province with their online form or on the Report Invasive mobile app.

Literature and Resources: