Tench

Water parameters

Minimum tank: 500 L per individual at harvest size.

Feed and growth

Feed protein

30% target

Daily feed (warm)

1.40% of body weight

Daily feed (cool)

0.60% of body weight

Max density

40 g per litre

A 2500 g adult eats about 35.0 g of feed per day at optimum. 10 fish at adult size: ~350 g daily.

Legality

Rules vary by jurisdiction and change over time. Verify with your local fisheries or wildlife authority before stocking.

Unlisted jurisdictions default to "check local regulations".

Origin and habitat

Native across Europe and western Asia, from Britain and Ireland east to the Ob and Yenisei, in warm, weedy, still or slow water over soft mud. A stocky cyprinid with tiny scales buried in thick, slimy skin and an olive-green body, it grows to about 84 cm at most, though average fish are nearer 40 cm, and it can live two to three decades. Tench root through the bottom for midge and caddis larvae, mayflies, beetles, dragonfly nymphs and molluscs, taking zooplankton when young. The heavy mucus coat gave rise to the folk name 'doctor fish,' from the old belief that ailing fish rubbed against tench to heal. The white, firm, well-flavoured flesh has made it a pond fish in Europe since the sixteenth century, still traditional in Central and Eastern European cooking, and a golden ornamental form is popular in garden ponds. Introduced to North America in the 1870s, tench is now spreading as an invasive in the Great Lakes and St. Lawrence.

Climate and outdoor ponds

Climate

temperate (handles seasonal swings)

USDA zones

4–10 (winter low around -34°C or warmer)

Heating needed

no

Cooling needed

no

Care notes

A hardy cool-to-warm-water food fish for European aquaponics, sitting between common carp and crucian carp in its habits. It is thermophilic, spawning and growing best around 20–29°C within a tolerance of about 4–30°C, and it spawns in batches once water passes 16–18°C, a female shedding several hundred thousand small eggs across several spawnings. Growth is modest, roughly 300–600 g in 18 to 24 months on carp pellet of 28 to 32 percent protein, with feed conversion around 2 to 3, behind common carp. Tench handle low oxygen better than most European fish, surviving brief spells under 1 mg/L, and tolerate a wide pH band. Stock around {density:10}-{density:20}. They are tough and disease-resistant, and the thick mucus may carry antimicrobial properties. Fingerlings come from carp hatcheries across Europe, and the fish is legal to farm throughout Europe without special permits. In Eastern Europe tench are sold above about 500 g, while Spanish and Italian markets prize smaller fish of 80 to 120 g. Slower-growing than common carp, tench suit extensive, traditional pond production and growers wanting a native European species; note that in North America and Australia it is treated as an invasive and restricted in several jurisdictions.

Further reading

• Aquaponics water chemistry: balancing pH for fish and plants
• Fish for aquaponics: tilapia vs everything else