Molecular analyses have demonstrated that Adriatic Brook Lamprey subpopulations inhabiting the upper Po River system in northwestern Italy are genetically divergent from L. zanandreai, and probably represent an as yet undescribed taxon (Rüber et al. 2023). They are retained as conspecific for the purposes of this assessment, pending definitive confirmation of their taxonomic status and geographic distribution.

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

The Adriatic Brook Lamprey is endemic to Europe, where it occurs in Italy, Slovenia and, marginally, in Switzerland. It does not approach the range thresholds for Vulnerable under Criterion B1 (extent of occurrence (EOO) < 20,000 km²) or D2. No explicit area of occupancy (AOO), population size or trend data are available, and the probability of extinction has not been quantified, therefore the remaining criteria cannot currently be applied.

However, a suspected population reduction based on continuing declines in habitat quality might approach or meet the threshold for Vulnerable under Criterion A2 (≥ 30% over the past 21 years; three generation lengths). 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 (A2ce) both globally and for the EU 27 member states.

The majority of this species' distribution comprises rivers draining to the northern Adriatic Sea basin (Italy, Slovenia, and southern Switzerland), where its range extends eastward from the Po River to the Soča (it. Isonzo) River. An isolated subpopulation is present in the Potenza River system in eastern Italy, and there is a record from the late 19^th century indicating that it may also be native to the adjacent Esino River.

During the mid-1990s it was understood to be restricted to small areas of the upper Po River system in Italy and a single location in Slovenia, but it has since been reported from a series of additional sites.

This species' current population size and trend have not been quantified, and the number of subpopulations is unknown.

Field observations indicate a marked decline in abundance at numerous locations in Italy and Slovenia since the mid-20^th century, and this pattern is suspected to be ongoing based on declining habitat quality in parts of its range.

Like other brook lampreys, this somewhat sedentary species is nonparasitic, spends its entire semelparous life cycle in freshwater and exhibits strong habitat fidelity with limited dispersal tendencies.

It is a specialised inhabitant of shallow, sometimes spring-fed, rivers, streams and backwaters typified by clean, flowing, well-oxygenated water and at least some patches of soft substrata comprising sand, silt or mud. It has been recorded at a range of altitudes, including some relatively high-gradient rivers draining to subalpine lakes.

Its life cycle is characterised by a blind, microphagous larval (ammocoete) phase, which spends several years buried in freshwater sediments of sluggish rivers and stream reaches. The larvae are believed to be generalist feeders, filtering algae such as desmids and diatoms, detritus and microscopic animals from the water column, although some benthic organisms may also be consumed. Metamorphosis occurs at the end of this growth stage, at which point individuals develop functional eyes and eventually emerge from the substrate as short-lived, non-trophic adults which spawn and die. Hatching occurs c. two weeks after egg deposition, and 1-3 weeks later the larvae emerge from the spawning substrate and drift downstream to settle in sheltered areas, where they bury into silt beds. The annual reproductive period appears to extend from February to March.

The extent and quality of habitat are estimated to be declining based on field observations plus the identified threats (see 'Threats').

This species is threatened by barrier construction, modification of river channels, groundwater abstraction and pollution from agricultural, domestic and industrial sources. In particular, the presence of dams, sills and weirs drives fragmentation of resident subpopulations while hindering natural flow and sedimentation processes, thus reducing the extent and quality of suitable habitat for egg deposition and larval development.

Exploitation of groundwater aquifers for irrigated agriculture has led to the dewatering of some formerly occupied locations in northwestern Italy, and potentially elsewhere within its range, since the turn of the century.

Moreover, extraction of riverine sand and other sediments for urban development may damage or eliminate ammocoete habitats, while dredging can negatively impact important spawning sites. Regulation of channels and banks may eradicate entire subpopulations through the loss of vital river features such as riffles and silt beds. Certain land management practices have resulted in increased soil erosion and siltation of gravel beds used for spawning.

Widespread pollution from agricultural, domestic and industrial sources has further reduced habitat quality. Eutrophication due to increased nutrient loads can cause spawning beds to be smothered by algae, and it is believed that ammocoetes are sensitive to high concentrations of environmental contaminants.

Increasing temperatures due to climate change could plausibly drive range shifting and impact physiological processes, but these impacts have not been studied in depth.

The species was harvested in the past.

In northwestern Italy, this species was formerly harvested for human consumption, but it is not currently used or traded.

This species is included in Appendices II (as Lethenteron zanandrai) and III of the Bern Convention, and Annexes II and V (originally as Lethenteron zanandrai in the latter) of the European Union Habitats Directive.

In Slovenia, it has been assessed as Endangered for the National Red Data List and nationally-protected since the mid-1990s. It was assessed as Vulnerable for the most recent (2022) iteration of the Red List of Italian Vertebrates, and Critically Endangered for the 2022 Swiss Red List of Fishes and Lampreys.

A number of subpopulations occur within the boundaries of protected areas, some of which are included in the European Union's Natura 2000 network.

It was included as a target species in the European Union-funded LIFE project 'SilIFFe' (LIFE14 NAT/IT/000809), which aimed to "strengthen the ecological network" of the Sile River, northeastern Italy. Annual surveys of the resident subpopulation were carried out during the project, but it is unclear if any direct conservation actions were taken.

This species has not been extensively studied, and it is recommended that future research should initially focus on establishing the locations of sites important for spawning and ammocoete development, the current population trend, and if necessary, the development of appropriate site-scale management measures for the extant subpopulations.