Tench

Tench facts

Also called

Doctor fish, from an old belief that its slime healed other fish. The golden tench is an ornamental pond strain. Tanche in French, Schleie in German, tenca in Spanish and Italian.

Family

Tincidae — long placed in the carp family, but recent genetic studies give it a family of its own.

Native range

Most of Europe and western Asia, east to the Yenisei. Naturally absent from Ireland, Scandinavia north of about 61°N, the eastern Adriatic basin, and western and southern Greece.

Introduced to

Ireland, North America, Chile, Australia, South Africa, Zimbabwe and Morocco. In Quebec it was brought illegally to a fish farm in 1986 and escaped through the Richelieu River into the St. Lawrence; it is now dense in the Richelieu, Lake Champlain and Lac Saint-Pierre, and has been seen as far as the Bay of Quinte on Lake Ontario. It is also established in British Columbia's Columbia and Okanagan systems and in parts of the western United States.

Habitat

Still or slow, warm water with mud or clay bottoms and lots of weed: lakes, ponds, gravel pits, canals and backwaters. It survives low oxygen better than almost any other fish — even where carp cannot — and often spends the winter half-buried in the mud.

Water temperature

Warm water; FishBase gives about 4–24°C (39–75°F). It spawns in early summer, once the shallows reach around 19–20°C (66–68°F).

Size

Most adults 20–45 cm (8–18 in); the largest measured about 70 cm (28 in).

Record

IGFA all-tackle world record: 4.64 kg (10 lb 3 oz), Dan Dellerfjord, Ljungbyån, Sweden, 1985. The British record is heavier: 6.899 kg (15 lb 3 oz), from a private fishery at Staines, Surrey, in 2001.

Lifespan

Long-lived for its size: tench up to 18 years old have been aged in a Norwegian lake.

What it eats

Bottom food, mostly taken at night: midge larvae, snails, pea mussels and other small animals, plus detritus and plant matter. Big adults often live mainly on molluscs.

Spawning

In summer, among dense weed in shallow still water. Each female lays batch after batch of small, sticky green eggs on the plants, every couple of weeks for about two months — up to 300,000 eggs in a season. The larvae hang on the plants until their yolk is used up.

Young fish

Fry stay hidden in thick weed and can grow fast. Males mature at 2–3 years and females at 3–7. A male has much larger, spoon-shaped pelvic fins that reach past the vent — the easy way to sex an adult tench.

Teeth and mouth

A small, fleshy mouth with one tiny barbel at each corner, and no teeth in the jaws.

Look-alikes

Carp has a long dorsal fin and big scales. Crucian carp is deep, bronze and has no barbels. Nothing else in fresh water combines olive-green colour, thick slime, tiny scales and small red eyes.

Eating

Edible, and once valued — it can be cooked like carp — but rarely eaten today; anglers almost always return tench.

Status

IUCN Least Concern; it has declined locally where rivers were engineered and backwaters lost.