Tench

Tench is an invasive freshwater fish species native to Europe and western Asia. Originally introduced to North America in the 19th century as a food and sport fish, tench later spread into Canadian waters after being illegally brought to a fish farm in Quebec in the 1980s. Since then, they have expanded through the St. Lawrence River system and have been detected in areas including the Bay of Quinte and Lake Ontario.

Tench are highly adaptable and thrive in warm, slow-moving, heavily vegetated waters such as wetlands, ponds, and sheltered shorelines. They feed along the bottom of waterbodies, consuming aquatic insects, snails, crustaceans, and plant material. This feeding behaviour can create competition with native fish species such as minnows, bullheads, and suckers, while also contributing to reduced water quality and increased algal blooms. Due to their ability to tolerate poor water conditions and spread rapidly, tench have become established in several regions of Canada and are now regulated under Ontario’s Invasive Species Act.