The Tench remains common throughout much of its substantial natural range, although the extent to which genetically-intact subpopulations persist is open to question. While the global population is estimated to be declining, this trend is not believed to approach the threshold for any threat category, and the overall population size remains very large. It is therefore assessed as Least Concern.

This species is purportedly native to Europe and parts of Northern, Western and Central Asia, although the precise limits of its natural range have been obscured due to extensive anthropogenic translocations over a period of several hundred years.

It is widely accepted to be native throughout the majority of the European region, with the exception of northern and western Scandinavia, northern European Russia, northern Great Britain, Ireland, the Balearic Islands, Corsica, Sardinia, the eastern Adriatic Sea basin, western and southern Greece, and the Crimean Peninsula. However, subpopulations inhabiting Great Britain, the Iberian Peninsula, the Apennine Peninsula and Sicily are typically referred to as cryptogenic, i.e., of uncertain origin.

In northern Asia its range encompasses the Ob and Yenisei river systems, roughly beneath the 60^th parallel north. In Western Asia it occurs in rivers draining to the Black Sea in Georgia and northern Türkiye, and rivers entering the western and southern Caspian Sea in Azerbaijan and northern Iran. In Central Asia it is present in the Ural River system in Kazakhstan.

Genetic research has revealed that the species contains two deeply divergent clades, comprising a western cluster occurring in Europe between Great Britain and Poland and an eastern grouping present from Eastern Europe to China. These clades derived from glacial refuges in Western Europe and the Black Sea, respectively, but are able to interbreed freely. In Europe, many Tench subpopulations contain an admixture of the clades, which is by all accounts the result of repeated anthropogenic introductions. While this admixture hampers confirmation of the species' native status in some areas, e.g., Great Britain, the Apennine Peninsula and Sicily, cryptogenic subpopulations from Portugal and Spain are derived exclusively from the eastern clade. Additional evidence obtained from historical accounts and records suggest that the Tench was introduced to Spain during the 16^th century.

For the purposes of this assessment, the Tench is therefore not considered native to the Iberian Peninsula, while its status in Great Britain, the Apennine Peninsula and Sicily is deemed uncertain.

Elsewhere, the Tench has been widely introduced to Ireland, the Mediterranean basin, Africa, Asia, Australasia and the Americas (see 'Use and Trade'). Although its establishment success has been variable, it is frequently considered invasive (see 'Habitats and Ecology'). For example, in the United States it has disappeared from many areas where it was formerly stocked but continues to expand its range in the Great Lakes region. In Norway it is recognised as the most widely-distributed non-native freshwater fish species.

A map comprehensively illustrating its current non-native distribution could not be produced within the scope of this assessment due to a lack of oversight regarding the relative success or failure of historical and ongoing introduction attempts, which are often unofficial and sometimes illegal (see 'Use and Trade').

This species' global population trend has not been quantified, but it is estimated to be declining within some parts of its native range (see 'Threats'). Localised declines have been documented in northern Iran, France, Poland, Czechia, Hungary, throughout the Balkan Peninsula, and the Danube Delta region, as well as in Italy (although in the latter its native status remains in question; see 'Distribution'). In some cases these downturns have been linked to reduced stocking in addition to the plausible threats (see 'Threats').

This relatively large-bodied species naturally inhabits lentic and sluggish lotic habitats including lowland river and stream channels, backwaters, floodplains, lakes and large ponds. It tends to avoid open environments and prefers shallow (< 2 metres depth) water with dense macrophyte beds or other forms of shelter and substrates of mud or silt. It is eurytopic, and able to breed prolifically in artificial lakes, ponds, and canals while tolerating diverse physical and chemical water parameters, including variations in temperature, oxygen concentration, pH and salinity. It can thrive in anoxic and eutrophic water bodies, and is apparently able withstand freezing or partial drying conditions by burying into soft substrates.

It is a generalist predator feeding primarily on invertebrates including annelids, crustaceans, insect larvae, and molluscs, alongside some detritus and plant material. Although largely a benthic feeder it is able to forage throughout the water column, including at the surface. A number of studies have suggested that foraging mostly takes place at night.

The successful establishment of Tench in non-native waters has been linked with a series of negative ecological consequences, particularly trophic overlap, i.e., competitive interactions, with native fish species and waterfowl. Predation by adult tench can drive significant declines in the abundance of crustaceans and molluscs, and reduced growth of submerged macrophytes through increases in inorganic nitrogen cycling and epiphytic algae. The eggs and larvae of other fish species may also be exploited as a food source.

Furthermore, the presence of high densities of Tench alongside other non-native fish species such as Rudd (Scardinius erythrophthalmus), Goldfish (Carassius auratus) and Common Carp (Cyprinus spp.) has been associated with the conversion of shallow, clear-water, macrophyte-dominated lakes and ponds to turbid, unvegetated habitats with increased eutrophication rates. These degraded habitat conditions negatively affect the abundance and richness of native fishes, especially sight predators, thus driving homogeneity in fish communities. Tench can also contribute to declining water quality through excessive predation on herbivorous zooplankton and disturbing sediments. It has also been associated with the transfer of microbial pathogens and parasites to piscivorous waterfowl and other fish species.

The Tench is long-lived and can reach at least 20 years of age. Within the native range male individuals attain sexual maturity between 2-5 years of age, and females between 4-7 years, with northern subpopulations maturing later. Males can be told apart from females by their extended pelvic fin rays. Spawning occurs from late spring to early Autumn (usually May-October, when water temperatures exceed 18°C) along shallow shorelines, backwaters and in floodplains. It is a highly fecund, fractional (i.e., females release batches of eggs at intervals during the reproductive period) spawner, and fully-mature females can release hundreds of thousands of eggs per year. These are deposited among aquatic vegetation, with individual females typically pursued by several males which compete to fertilise them. Hatched fry remain in warm, shallow, marginal habitats with dense vegetation and/or woody structures during the early growth period, and initially feed on zooplankton. In lakes, recruitment success displays a positive relationship with the extent of littoral habitat.

This species is threatened by habitat modification in some parts of its natural range. In particular, the loss of floodplains and other freshwater wetlands due to dam construction, water abstraction and direct drainage has significantly reduced the extent and quality of spawning and nursery habitat available to riverine subpopulations. Canalisation and other forms of shoreline alteration (e.g., construction, human recreation) in both lakes and rivers decrease the extent of suitable foraging zones for individuals of all age classes.

Eutrophication and other forms of pollution can negatively impact macrophyte beds which constitute the most favoured Tench habitats, and render the species more vulnerable to competition and predation. These issues can be exacerbated by introduction of non-native fish species.

The Tench is further threatened by the homogenising effect of human-aided dispersal through introgression with genetically admixed hatchery stocks, some of which comprise domestic strains, and the widespread translocation of wild subpopulations to new areas. Uncontrolled and sometimes illegal restocking continues in many areas, where the rate of hybridisation with wild subpopulations is likely to be high.

This species has a long history in the aquaculture and cuisine of central and eastern Europe, having been reared in artificial ponds since the Middle Ages. In addition, it has for several centuries been prized as a delicacy and element of local culture in the regions of Extremadura (southwestern Spain) and Piedmont (northwestern Italy), where it is traditionally reared in low-output monoculture ponds and marketed at a relatively small size. In Piedmont, the Tinca Gobba Dorata del Pianalto di Poirino (Golden-humped Tench of the Poirino highlands) is the only fish product in Italy to have been granted the European Union's Protected Designation of Origin. Elsewhere, the Tench has typically been maintained as a supplementary species in artificial pond polycultures alongside common carp (Cyprinus spp.) and other species, with intensive production having been largely limited by its slow growth in captivity.

The Tench is also heavily targeted by recreational fishers who prize it as a strong, hard-fighting fish. It has thus been widely-stocked both within and outside its native range, with such efforts including legitimate translocations by official entities in order to establish sports fisheries or aquaculture facilities, illegal stockings by private citizens and accidental introductions alongside other fish species (see 'Distribution'). Stocking has in some cases been driven by concerns over recruitment due to loss of natural spawning habitat (see 'Threats').

Although global production has generally remained low (e.g., c. 2,500-3,200 tonnes per year from 2013-2017), the Tench has in recent decades been considered among the prime candidate species for diversification of freshwater aquaculture in Europe and China, having been introduced to the latter during the late 1990s. This increasing market demand has led to a focus on improving productivity under controlled conditions, including the development of artificial rearing techniques and a number of domesticated strains. The latter include 'golden' and 'blue' colour forms that originated in the Czech Republic and subsequently became popular in the ornamental fish trade.

In the United Kingdom, the Tench is sometimes referred to as the "doctor fish", a name derived from the false historical belief that the mucous secreted by its skin possesses healing properties.

The tench is considered of conservation concern and protected at the national scale in Serbia, where fishing for the species has been prohibited since 2009. There is an increasing interest in conservation management in other countries where declines have been reported, but specific field measures do not appear to be in place. Broader efforts to restore floodplains and other wetlands in river systems to which the tench is native are likely to benefit the species through re-establishment of former foraging, spawning and nursery zones.

Waters exploited for recreational tench angling are commonly restocked throughout much of its natural range, but such efforts do not generally consider conservation management outcomes (see 'Threats').

A gene- and cryobank for the species, with conservation as a stated aim, is currently maintained at the National Centre for Biodiversity and Gene Conservation in Gödöllő, Hungary.

Future species-specific conservation management efforts should ideally be based around the prior identification of genetically-pure wild subpopulations.