Molecular evidence suggests that this species is very closely-related to the congener Alburnus albidus, and additional systematic research is recommended (Geiger et al. 2014).

The congeneric taxon Alburnus maximus Fatio 1882, described from Lake Lugano in Italy, is considered to be a valid species by some published sources. It is here treated as a synonym of A. arborella pending future research, as recommended by Buj et al. (2010) and Lorenzoni et al. (2019).

Global and European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

The Italian Bleak does not approach the range thresholds for Vulnerable under Criterion B1 (extent of occurrence (EOO) < 20,000 km²) or D2, and Criterion B2 is precluded by its uncertain area of occupancy (AOO). The population size is believed to exceed 10,000 mature individuals, and hence does not approach the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Although no explicit population trend data exists for its overall range, it is possible that a suspected ongoing reduction based on field observations, declining habitat quality and the effects of introduced taxa may approach or meet the threshold for Vulnerable under Criterion A2 (≥ 30% over the past 15 years = three generations), based on declines noted in Italy and Switzerland. As a result of this data uncertainty, Least Concern and Vulnerable are equally plausible Red List categories for the present assessment, and this species is assessed as Near Threatened.

This species is endemic to river systems of the northern Adriatic Sea basin, where its range extends from the Chienti River system in the Marche region, eastern Italy, to the Istrian Peninsula. Further south, an isolated subpopulation inhabits the Zrmanja River system in Croatia.

Introduced subpopulations are established throughout much of western and southern Italy, northern Sardinia (Temo River and artificial Lake Liscia), and the Lika region (Ričica River and elsewhere), Croatia.

This species' population size is unknown, but is understood to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals), and the number of subpopulations is unclear.

The current global population trend has not been quantified, but is suspected to be declining based on field observations, declining habitat quality and the effects of introduced taxa (see 'Threats'). For example, in Italy the area of occupancy (AOO) has continued to decline since the mid-1990s, and a minimum reduction of 30% is estimated within the past three generations (c. 15 years). In Switzerland its abundance has declined by an estimated 80% over the last three generations.

The downturn has been particularly evident in subalpine lakes of the Po River system, where it has been extirpated from some locations, e.g., lakes Garda, Lugano, Monate, Piano and Varese. This followed a period between the 1960s and 1980s when the abundance of some lacustrine subpopulations increased due to rising productivity driven by eutrophication, but later crashed (see 'Habitats and Ecology'). Some of the affected subpopulations have since recovered to a limited extent (see 'Conservation').

It apparently remains abundant in most other Italian river systems within its native range, but future declines are considered to be plausible (see 'Threats').

No significant declines have been reported in Slovenia or Croatia, and its non-native range appears to be expanding (but see 'Taxonomic Notes').

This small-bodied, gregarious species is generally considered to be eurytopic and inhabits a range of habitat-types from large subalpine lakes to lowland river channels and small streams. It also occurs in highly-modified environments such as artificial reservoirs and canalised river stretches, and tends to be particularly abundant in eutrophic and mesotrophic waters.

It is an omnivorous, opportunistic forager which typically feeds in open water close to the surface. It preys on zooplankton and free-swimming invertebrates, plus flying and terrestrial arthropods which fall into the water. Rising zooplankton biomass during the enrichment phase of eutrophication can drive concurrent increases in this species' abundance (but see 'Threats').

In Italy, it is considered to be invasive outside of its native range, since it represents a major threat to the congeneric Southern Italian Bleak (Alburnus albidus) through genetic introgression and hybridisation.

Sexual maturity is attained at age 1-2+, and fecundity ranges from c. 1,000-3,000 spawned eggs per female

The annual reproductive period extends from spring to summer with a peak during Juneand, and generally coincides with water temperatures rising above 15°C. Some subpopulations undertake upstream or lateral migratory movements to spawn during the night or early morning in shallow tributaries or along lake shorelines.

Spawning sites most often comprise stretches with clean gravel or sand substrata over which the eggs are deposited, although submerged plants or woody debris are sometimes used. Reproductive adults form aggregations which remain in the vicinity of spawning sites for several consecutive days.

The precise factors driving the decline of this species' lacustrine subpopulations in northern Italy have not been confirmed, although a series of plausible threats have been identified.

In particular, rapid industrialisation and urbanisation during the mid-20^th century increased nutrient loads and drove eutrophication through discharge of untreated wastewater. While the Italian Bleak may have initially benefitted from the associated rise in zooplankton biomass, many of its favoured spawning sites were later lost due to overgrowth of benthic algae or emergent shoreline macrophytes such as reeds. Moreover, mass mortality events caused by pathogens linked to eutrophication were observed at some locations, e.g., lakes Lugano and Maggiore, during the 1970s.

Until the 1990s, most of the Italian subalpine lakes were also heavily polluted by industrial contaminants, e.g., DDT in Lake Maggiore, copper and ammonium sulphate in Lake Orta. Some spawning sites are also likely to have been destroyed by urban development of lake shorelines.

A number of non-native fishes have become established within the Italian Bleak's range. These include the Eurasian Pikeperch (Sander lucioperca), Largemouth Bass (Micropterus salmoides), Pumpkinseed (Lepomis gibbosus), Black Bullhead (Ameiurus melas) and Wels Catfish (Silurus glanis), all of which are known to predate on native species, plus Common Roach (Rutilus rutilus) and whitefish (Coregonus spp.), which compete for similar resources. Any negative impact of these introductions may be more pronounced in lakes, since evidence obtained from some parts of the Po River system suggests that fluvial subpopulations are not significantly affected by the presence of non-native species.

However, fluvial subpopulations are understood to be threatened by reduced flows and loss of suitable spawning habitat driven by water abstraction, extraction of gravel and sand from riverbeds, removal of riparian vegetation, and pollution from agricultural, industrial or urban sources.

This species was, prior to its decline, among the most important commercial species in Italian subalpine lakes, but these fisheries are today dominated by non-native species.

This species is nationally-protected in Croatia.

It occurs within the boundaries of various protected areas, some of which are included in the European Union's Natura 2000 network (see 'Threats').

It is assessed as Vulnerable in the 2022 Red List of Italian Vertebrates, and Critically Endangered in the 2022 Swiss Red List of Freshwater Fishes.

Some conservation efforts took place in perialpine lakes of the Po River system, Italy, during the late 1990s and early 2000s. For example, in Lake Como measures implemented in 1997 included installation of artificial spawning beds and supplemental feeding for juveniles during winter.

In addition, several hundred thousand eggs and fry were harvested from the Tresa River and released into lakes Lugano, Monate and Varese between 2000 and at least 2004. A 2005 report suggests that adult individuals were subsequently observed in lakes Monate and Varese, but the current status of these subpopulations is unclear. Ex situ breeding attempts which took place during the same period were largely unsuccessful.

A project to reinforce the Lake Garda subpopulation applying similar techniques has been underway since 2019, with artificial spawning beds installed and eggs transferred to the lake from elsewhere.

At the broader scale, the trophic status of most Italian perialpine lakes has improved since the 1980s, due to the establishment of processing facilities for urban waste plus other remedial measures such as restricting the use of phosphorous in detergents.

Future research and monitoring efforts are required in order to understand this species' global population trend.