Tench (Tinca tinca) are a widespread species of freshwater fish native to temperate Europe and Asia. Popular as an angling species, they have been introduced to a number of countries as a sport fish. Their omnivorous diet and tolerance of a wide range of environmental conditions has lead to some countries labelling tench an invasive species, due to concerns over competition with native fish.
Description Tench are a heavy-built, thick-set fish with a small barbel at each corner of the mouth. Colour ranges from deep blackish-olive to pale golden tan, with a bright reddish eye. The body is slimy, with the small scales being covered by a thick layer of mucus. Very large specimens may reach 800mm in length and 8kg in weight (McDowall, 2000).
Occurs in: lakes, water courses, wetlands
Habitat description Inhabits slow-moving, weedy waterways with muddy substrates. Found in streams, lake shallows and lagoons. Able to tolerate low oxygen concentrations and a wide range of temperatures, from 4 to 24°C. Often found amongst weeds or in deep holes. (FishBase, 2004; McDowall, 2000). The habitat for tench in New Zealand was reviewed by Rowe (2004).
General impacts Impacts specific to tench are difficult to find, as this species is often lumped together with others in the Cyprinidae family, such as koi and common carp. In Australia it is thought that tench may directly compete with trout and native fish for food resources (IFS, 2000). The ability of tench to survive in degraded environments causes some confusion, as it is unclear whether they contribute to this degradation or simply inhabit a niche that native fish cannot occupy. Most impacts are likely to be related to the wide range of organisms consumed by tench. An experimental study by Bekliogu & Moss (1998) showed that tench can increase periphyton (algal) biomass through selective predation on gastropods, which keep periphyton under control through grazing. This 'trickle-down' effect could have negative impacts on aquatic communities if it occurs to a significant extent in the wild. Impacts of tench were reviewed by Rowe (2004). There is no evidence that they affect other fish directly, however, a number of studies have implicated them in water quality decline.
Uses Highly valued as a sports fish by coarse fish anglers.
Notes Becomes dormant in winter, staying in the mud without feeding (FishBase, 2004).
Geographical range Native range: Occurs throughout temperate Europe and across Asia to China (McDowall, 2000). Known introduced range: Introduced to a number of countries around the world including Chile, Canada, Australia, India and New Zealand.
Introduction pathways to new locations Smuggling: Anglers may illegally introduce tench to stock private ponds. Stocking: Tench may be stocked in ponds and lakes for recreational angling.
Local dispersal methods Intentional release: Introduced to many locations as a sports fish by angling organisations. Intentional release: Introduced to many countries as a sports fish by angling organisations. Natural dispersal (local): Can colonise new areas in connected water bodies.
Management information Densities of tench declined markedly following complete weed removal in a small 2 ha lake (Rowe, 2004) and this was attributed to shag predation. All tench were eliminated by rotenone. (Rowe and Champion, 1994).
Nutrition Consumes a wide variety of benthic organisms (crustaceans, insect larvae, midges), as well as aquatic snails, small fish and algae (FishBase, 2004).
Reproduction External fertilisation. Spawns during summer, releasing thousands to millions of tiny eggs (c. 1mm diameter) amongst aquatic weeds. Fry hatch in around a week (McDowall, 2000).
Lifecycle stages Sexual maturity attained at around the age of two. Long-lived, with individuals surviving to 20 years of age or more (McDowall, 2000).
Reviewed by: Dr. David Rowe, NIWA (National Institute of Water & Atmospheric Research). Hamilton New Zealand.
Principal sources: McDowall, R. M. 2000. The Reed field guide to New Zealand freshwater fishes. Auckland, Reed. FishBase, 2004. Species profile Tinca tinca Tench Rowe, D.K., 2004. Potential effects of tench Tinca tinca in New Zealand freshwater ecosystems. NIWA Client Report No HAM2004 005. National Institute of water and Atmospheric Research Ltd., Hamilton, New Zealand. 27 pp.
Rowe, D.K and Champion, P.D., 1994. Biomanipulation of plants and fish to restore Lake Parkinson: a case study of its implications. In Collier, K.J (eds), Restoration of Aquatic Ecosystems, Science and Research Series, Department of Conservation, New Zealand.
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)