Tench

Tench thrive best in enclosed, preserved waters, with a clayey or muddy bottom and with abundant vegetation. This species is rare in clear waters across stony ground, and is absent altogether from fast-flowing streams. During summer months, the tench seeks cooler temperatures by concentrating in deep holes and shaded areas. It tends to be inactive during the day, resting in favored habitats such as dense aquatic vegetation, and forages for food after dusk.

The tench is tolerant of low levels of dissolved oxygen, and are reported that the species can survived in waters with a low oxygen level that would quickly kill other fishes. The Tench is a remarkably hardy fish. Historical accounts from England claim fishmongers would bring individuals to market and return the unsold fish back into water to live (presumably until their next trip to market. Live tench have also reportedly been shipped during winter in boxes of weeds. Individuals from northern Europe can withstand temperatures near freezing and have been reported that the species burrows into the mud during winter for protection against the cold where it remains in a motionless condition similar to hibernation. The species is also reported to be tolerant to low levels of salinity.

The tench was originally imported into North America from Germany by the U.S. Fish Commission in 1877 and distributed to at least 36 states by 1896. Subsequent stocks probably had other origins. For example, at least one other introduced stock was imported from Italy. Intentional stocking and accidental escapes have increased its distribution in the U.S. The tench has been reported in at least 39 states, but most introductions were unsuccessful, and the species has maintained reproducing populations in only a few areas. In Washington State the tench is considered an aquatic nuisance.