Since the mid-2000s, rudd subpopulations from the Adriatic and Ligurian/Tyrrhenian sea basins of Italy have been referred to as Scardinius hesperidicus Bonaparte 1845 and S. scardafa (Bonaparte 1837), respectively. However, these two taxa are diagnosed only on the basis of minor meristic and molecular characters, and their taxonomy has not been definitively resolved (Ketmaier et al. 2003, 2004, Bianco 2014, Geiger et al. 2014, Lorenzoni et al. 2019).

It has also been suggested that the introduction of S. hesperidicus caused S. scardafa to go extinct throughout its native range during the 20^th century. The only extant S. scardafa subpopulation thus occupies Lake Scanno in Abruzzo and purportedly originates from nearby Lake Fucine, which was artificially drained during the late 1800s (Bianco 2004, 2014).

However, there is no clear evidence that this translocation took place, and it is perhaps unlikely that the introduction of S. hesperidicus to some locations within the range of S. scardafa would have driven the latter to extinction within the space of a few decades (Lorenzoni et al. 2019).

Moreover, the results of a comparative analysis demonstrate that Italian Rudd subpopulations exhibit a defined phylogeographic structure, with no significant anthropogenic influence on their native distribution (Stefani et al. 2004). In addition, older literature indicates that there exists natural variation in meristic characters, which have not been fully-investigated (Lorenzoni et al. 2019)

Molecular research also suggests that both S. hesperidicus and S. scardafa are closely-related to S. plotizza, which is native to the Neretva River system in the western Balkan Peninsula. Therefore, additional systematic research is recommended (Geiger et al. 2014).

Global and European regional assessment: Least Concern (LC)
EU 27 regional assessment: Least Concern (LC)

This species 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. Although it may be declining in some parts of its range, there is no evidence that any population size reduction approaches the threshold for Vulnerable under Criterion A (≥ 30% over the past 10 years or three generations). The population size does not approach the thresholds for Vulnerable under Criterion C (< 10,000 mature individuals) or D1, and there exists no quantitative analysis of extinction probability which would permit application of Criterion E.

Therefore, the Italian Rudd does not currently meet the thresholds for any Red List criteria, and it is assessed as Least Concern for both Europe and the EU 27 member states.

For the purposes of the present Red List assessment, this species is treated as endemic to the northern Adriatic Sea basin in Italy, where its range extends from the Vomano River in Abruzzo to the Isonzato River in Friuli-Venezia Giulia.

It is also widespread in rivers draining the Ligurian and Tyrrhenian slopes of Italy, including major systems such as the Arno, Ombrone, Tiber and Volturno, but the origin of these subpopulations is currently uncertain (see 'Taxonomic Notes').

Elsewhere, it has been introduced to the Guardialfiera accumulation lake in the Biferno River, southeastern Italy, plus a number of periapline lakes located north of the Alps in France and Switzerland, e.g., lakes Bonlieu, Chalain, Saint-Point, Remoray, Geneva and Bourget in the Rhône River system, lakes Rousses, Brenet, Neuchâtel, Morat, Biel, Thun and Zurich in the Rhine River system, and Lake Sils in the Danube River system.

This species' population size is unknown, but it clearly 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.

There is reportedly evidence of declining abundance in parts of the upper Po River, but no specific details became available during the course of this assessment.

This benthopelagic, gregarious species inhabits lentic environments, including deep, naturally oligotrophic perialpine lakes, slow-moving reaches of large perennial river channels, backwaters, oxbows and side-arms. It readily colonises channelised river stretches, artificial drainage canals and fluvial accumulation lakes created by dams.

Individuals inhabiting periapline lakes tend to aggregate in the littoral and benthic zones to depths of c. 30 metres, often in the vicinity of reed or macrophyte beds. In smaller, shallower lakes they may also occupy the pelagic zone, but tend to be absent from open water in larger systems.

It is understood to be an omnivorous generalist in terms of diet, feeding on a variety of planktonic and benthic invertebrates, higher plant material and insects taken at the water surface.

The maximum recorded age is 15 years, and adult individuals reportedly mature at age 2-3+. The annual reproductive period is believed to extend from March to July. It is a fractional, polygamous spawner, and the eggs are deposited among submerged vegetation.

In its non-native range, this species hybridises with the Eurasian Rudd (Scardinius erythrophthalmus).

This species is understood to be somewhat resistant to anthropogenic habitat alterations, but is plausibly threatened to some extent by lake and river regulation. The construction of dams, sills, weirs and other barriers throughout its range has severely altered natural flow and sedimentation regimes, fragmented subpopulations, and conceivably reduced the extent of suitable habitat for all life stages. The water level of some perialpine lakes is controlled for domestic water supply, irrigation and hydropower generation, leading to marked fluctuations and interfering with the extent of available littoral habitat and appropriate spawning sites.

Hydroelectric dams have created unnatural fluctuations in discharge and water temperature (hydropeaking and thermopeaking) which bring about artificial dewatering of downstream river stretches and loss of stable nursery habitat for juvenile fishes. The quality of habitat has been further diminished by bank stabilisation, channelisation and other efforts to enhance flood protection or exploit water resources, which has reduced the extent of spawning sites through a loss of connectivity between main river channels and their floodplains.

Since the 1950s, at least 19 non-native fish species have colonised the rivers and perialpine lakes of northern Italy, leading to reduced abundance in the majority of native taxa through introgressive hybridisation, competition, predation, habitat degradation or parasite transmission. These declines have been exacerbated by widespread agricultural, domestic and industrial pollution during the 20^th century, some of which persists today. For example, all large perialpine lakes in the Po River system have suffered from anthropogenic eutrophication driven by the development of industry and agriculture, which led to increased loading of nutrients and other contaminants from domestic wastewater and runoff.

Field observations indicate that the Italian Rudd has not been significantly-impacted by these events, since it remains present throughout its native range and is relatively abundant at some locations. However, a shortage of analyses based on temporal abundance trends precludes any definitive conclusion.

This species is not generally used or traded, although larger individuals are sometimes harvested as bycatch by commercial fishers operating on some perialpine lakes.

It is also utilised in recreational fisheries, although no stocking is known to take place.

This species was assessed as Near Threatened for the 2022 Red List of Italian Vertebrates and Vulnerable for the 2022 Swiss Red List of Freshwater Fishes.

It is present within the boundaries of various protected areas, some of which are included in the Ramsar Convention on Wetlands of International Importance and/or the European Union's Natura 2000 network.

Some subpopulations may have benefitted from improvements in habitat and/or water quality associated with implementation of the European Union Water Framework Directive 2000/60/EC, such as efforts to restore fluvial connectivity through barrier removal. Moreover, investment in wastewater treatment facilities and other policy-led measures since the 1980s has driven water quality improvements in most of the Italian perialpine lakes, some of which have returned to their natural oligotrophic state while others remain mesotrophic.

A deeper understanding of this species' demographics (population size and trend) and life history would likely prove useful in the development of future management efforts. However, confirmation of its taxonomic status should ideally be treated as a research priority in order to inform appropriate decision-making.