Although this species' population trend may be decreasing due to habitat degradation, there is no evidence that the rate of decline approaches the minimum threshold for Vulnerable under Criterion A (≥ 30% over the longer of 10 years or 3 generations). It does not approach the range thresholds for Vulnerable under Criterion B (extent of occurrence (EOO) < 20,000 km², area of occupancy (AOO) < 2,000 km²) or D2. The population size far exceeds 10,000 mature individuals, hence it does not approach the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Therefore, the Ide does not currently meet the thresholds for any Red List criteria, and it is assessed as Least Concern.

This species has a substantial natural range extending eastward from Europe to the Russian Far East, within which it inhabits rivers draining to the North, Baltic, Black, Caspian, White, Barents, Kara and Laptev sea basins.

Its distribution is limited by the Rhine-Meuse-Scheldt River system to the west, Sweden and Finland to the north, the Lena River system to the east, and the Alps, northern Black and Caspian sea basins and Aral Sea basin to the south.

Outside of its native range, introduced subpopulations exist in parts of Great Britain and France. Despite earlier reports, it does not appear to be established in Italy or Spain, and may no longer occur in the United States or New Zealand.

This species' population size is unknown, but it far exceeds the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified, and the number of subpopulations is unclear.

It has declined significantly across some of its range (e.g., Belgium, the Netherlands, Finland, Estonia, Latvia, Poland, Czech Republic, Slovakia, Aral Sea basin) since the mid-20^th century.

Western European subpopulations today appear to have stabilised at comparatively low levels of abundance, while there are recent signs of recovery in parts of the Baltic region (see 'Conservation').

Elsewhere, a recent documented expansion northwards in the Lena River system, eastern Russia, has been linked to increased rainfall and warming water temperatures driven by climate change.

This relatively large-bodied species is benthopelagic and mostly potamodromous, although anadromous subpopulations exist in the Baltic, Azov and Caspian seas.

It inhabits a range of environments including lowland rivers, floodplains and nutrient-rich lakes, artificial canals and reservoirs, estuaries and coastal zones of brackish seas. There is evidence to suggest that it may enter deeper waters of the Baltic Sea.

While some individuals are reported to be predominantly sedentary outside the annual reproductive period (see below), others are highly mobile and have relatively large home ranges.

It generally exhibits a preference for slow-moving to still waters, and can withstand a wide range of water temperatures from 0-35°C, with a preferred range of 4-20°C. The maximum tolerated salinity is c. 15%, and along brackish coastline of eastern Zealand, Denmark, thousands of anadromous individuals are regularly killed due to influxes of higher salinity water from the North Sea. It is intolerant of low dissolved oxygen concentrations, and this trait may have contributed to some local declines (see 'Threats').

It is a visually-oriented opportunistic omnivore feeding on aquatic and terrestrial invertebrates, fish eggs and larvae, algae, higher plants, seeds and detritus, while larger individuals often prey on smaller fishes. The precise composition of the diet varies with ontogeny, location and season.

This species is relatively long-lived (maximum recorded lifespan 29 years) and slow-maturing (age 1-10+ but normally at least age 3+, depending on latitude). Males tend to mature one year earlier than females. Older individuals can weigh in excess of three kilogrammes, and absolute fecundity ranges from 15,000-260,000+ eggs per individual female depending on a series of factors including growth rate, size at maturity, life-history type and/or geographic origin.

The annual reproductive period is triggered by rising water temperatures and can occur anytime from February to June, depending on location. It is preceded by sometimes lengthy upstream or downstream migrations of nuptial adults to spawning sites comprising backwaters and floodplains of rivers, or marshy vegetated areas of lakes. In Estonia, a considerable number of individuals spawn in semi-enclosed brackish bays that are temporarily flooded with freshwater from snowmelt and spring rains.

Males arrive at spawning sites earlier and leave later than females. Whereas some subpopulations display fidelity to particular spawning sites, others use different sites on an annual basis.

Spawning itself takes place during a brief period of 3-9 days and occurs both during the day and at night. The adhesive eggs are attached to substrata which can include gravel, stones, algae or vegetation. The adults do not guard the eggs, and embryonic development varies with ambient water temperature, e.g., c. 14 days at 10-12°C. The larvae attach to submerged surfaces and become free-swimming shortly before absorption of the yolk sac at a size of 6.1-6.9 mm standard length.

Post-spawning adults return to their foraging grounds, and typically retreat to deep depressions and other refuges in lake or river beds during winter.

Early-stage larvae may drift downstream and are commonly encountered in freshwater tidal estuaries, while free-swimming fry and juveniles form large aggregations in shallow littoral habitats. In the Baltic region, young-of-the-year individuals migrate to the sea at different stages within the first year of life, and subsequently undertake annual non-spawning migrations to freshwater environments alongside reproductive adults.

Successful recruitment has been strongly linked to the prevalence of stable water levels and temperatures during the reproductive period.

The Ide occasionally hybridises with related species, including Common Bream (Abramis brama), Eurasian Asp (Leuciscus aspius), Common Dace (Leuciscus leuciscus), Common Roach (Rutilus rutilus), and Eurasian Rudd (Scardinius erythropthalmus).

This species is threatened by river regulation and other forms of habitat degradation, which have driven widespread loss of the heterogeneous, interconnected fluvial habitats required to complete its life-cycle.

In particular, the construction of dams, weirs and other barriers has altered natural flow and sedimentation regimes, blocked migration routes, fragmented subpopulations, and reduced the extent of suitable habitat for all life stages. The quality of available habitat has been further diminished by bank stabilisation, channelisation and other efforts to enhance flood protection or river transportation links.

It is also likely to have declined due to widespread agricultural, domestic and industrial pollution during the 20^th century, some of which persists today. For example, increasing nutrient levels have driven eutrophication and increased water turbidity throughout its range, resulting in reduced foraging success and a decrease in the quality of foraging and spawning sites. Diminished oxygen concentrations associated with these conditions during early development of eggs and larvae may negatively impact recruitment.

Certain herbicides, pesticides and industrial pollutants can cause direct mortality or impair reproduction when present in sufficient concentrations.

Management efforts based on restocking (see 'Conservation') might also threaten some subpopulations due to the potential for inbreeding, loss of genetic diversity and introduction of non-native genetic lineages or pathogens.

In Estonia, overfishing during the annual spawning run is considered responsible for the collapse in stocks of anadromous subpopulations since the 1980s.

This species is harvested commercially within some parts of its range, e.g., Finland, Latvia, Poland, Russian Federation, although in Europe its use as a food fish is diminishing due to a combination of market trends and reduced landings.

In other countries, e.g., the Netherlands, Estonia, Slovakia, Kazakhstan and Uzbekistan, the commercial fishery is today negligible in the wake of stock collapses since the mid-20^th century (see 'Threats').

It is a popular target for recreational anglers, and has been regularly translocated both within and oustide its native range for this purpose.

It is reared artificially in hatchery facilities using hormones and other techniques for restocking of native subpopulations (see 'Conservation') and recreational fisheries. In some cases (e.g., Belgium, Poland) these efforts have been ongoing for several decades, while in others (e.g., Lithuania) they have been recently established. The origin of the fish used for restocking is not always taken into account, and this may represent a threat to some subpopulations (see 'Threats').

Ornamental colour forms have been reared in captivity since the 18^th century, and today are produced commercially in Belgium, the Netherlands, Germany, Italy, New Zealand and the United States. They are marketed as 'blue' or 'golden' orfe for the recreational fisheries and garden pond sectors.

This species is considered to be locally or nationally threatened in a number of areas, including Flanders (Belgium), the Netherlands, coastal Poland, the Czech Republic and Slovakia. It is protected under national legislation in Czech Republic.

Closed fishing seasons timed to coincide with the annual reproductive period are in place in Belgium and the Netherlands, while minimum size limits are established in Wallonia (Belgium), Estonia, Latvia, Lithuania and Poland. There are also daily bag limits in place in Poland, and in Estonia a number of no-fishing zones have been established.

Recent signs of recovery have been reported in coastal parts of Estonia and Lithuania, with observed increases in the number of juveniles since the mid-2010s.

It occurs within the boundaries of numerous protected areas. In European Union member states, some of these are included in the Natura 2000 network, and it is also likely to have benefitted from efforts to improve the ecological status of rivers within the structure of the European Water Framework Directive.

The latter legislation was implemented in 2003 and has alongside a general decline in heavy industry resulted in improving water quality across much of its range. Pollution has in many areas been reduced, while management actions focussed on freshwater fishes have included measures to improve habitat quality, e.g., restoration of spawning sites or stream banks, or connectivity, e.g., dam-removal projects or installation of nature-like fishways to re-establish migration routes.

In some countries, these procedures have been supplemented by ex situ methods to reinforce declining subpopulations or repopulate locations in the wake of extirpation events. Such projects have typically involved supportive rearing followed by restocking with captive-bred juveniles and larvae, or the release of fertilised eggs. In Poland, restocking efforts have been ongoing for several decades, and are considered to have driven observed increases in abundance and biomass in some inland rivers. Conversely, there have been no observed improvements in Belgium despite restocking programmes being active since the 1990s.

The potentially negative effects of long-term restocking on the genetic diversity and fitness of wild subpopulations do not appear to have been studied, but might be worthy of investigation based on observations in other species such as Common Nase (Chondrostoma nasus). In addition, restocking may have little long-term impact if habitat conditions remain unsuitable, and the development of integrated management approaches could prove effective.

Precise details regarding this species' population status across most of its range are unavailable, therefore the implementation of monitoring efforts is recommended. Given the extent of its range, such efforts would be best coordinated at local or regional scales.