This taxon was considered to be a synonym of the congeneric Peloponnese Chub (Squalius peloponensis) in the recent past, and its systematic status remains in need of review.

Individuals collected in the Vouraikos River system (see 'Geographic Range') have recently been identified as S. moreoticus, but molecular research suggests that this subpopulation is probably conspecific with S. peloponensis (Tsoupas et al. 2022).

Moreover, the two species cannot be differentiated by external morphology. Samples collected from Lake Stympahlia prior to the drying event in 1989 (see 'Population' and 'Threats') should ideally be reanalysed for comparative purposes, since they were in the past recovered as genetically distinct (Doadrio and Carmona 1998).

The Stymphalia Chub has a restricted range (extent of occurrence (EOO) c. 1,503 km², area of occupancy (AOO) c. 72 km²), which meets the thresholds for the Endangered category under Criterion B1 (EOO < 5,000 km²) and Criterion B2 (AOO < 500 km²). It is present at two locations where the quality of habitat is estimated to be declining.

Therefore, this species is assessed as Endangered under Criterion B (B1ab(iii)+2ab(iii)).

This species is native to the Lake Stymphalia (el. Στυμφαλία) basin and nearby Vouraikos (el. Βουραϊκός) River system in the northeastern Peloponnese, Greece.

This species' current population size and trend have not been quantified.

The Lake Stymphalia subpopulation was understood to have been extirpated after the lake dried out during the late 1980s (see 'Threats'), but chubs have subequently been observed in the system. It has been suggested that these derive from introductions by local residents after the lake was rewetted, but it is plausible that a small number of individuals survived in the headwaters of perennial tributary springs and were able to recolonise naturally.

Lake Stymphalia is located within a shallow limestone polje, and is fed by a small number of perennial karst springs plus some intermittent torrential streams. The surface area is c. 3.5 km², but this can extend to 5 km² during high water levels in spring, and its average depth is c. 1.5 metres. A ponor in the southwestern part of the basin used to comprise the primary outflow, but it is today active on an occasional basis due to artificial water regulation. The lake's level fluctuates naturally depending on environmental conditions, and it is prone to periodic drying. During these events, surrounding springs are likely to act as refugia for native fish species. The upper reaches of these springs are perennial, and aquatic habitats are characterised by slow to moderate flow and stony substrata (see 'Threats'). The lake formerly contained extensive submerged macrophyte beds, but these have gradually disappeared since the mid-20^th century and stands of Common Reed (Phragmites australis) now dominate.

The Vouraikos is a relatively short (c. 46 km) river, and its lower reaches flow through a steep-sided gorge before entering a narrow lowland floodplain. The gorge area is particularly well-preserved (see 'Conservation'), and the Stymphalia Chub primarily inhabits flowing reaches with clear water.

Little is known of this species' life history, but it is believed to achieve sexual maturity at age 1+, with the annual reproductive period extending from April to May.

Its diet comprises a broad variety of aquatic invertebrates and smaller amounts of plant material.

This species is primarily threatened by habitat modification, pollution and changes in the hydrological regime of Lake Stymphalia due to water abstraction. Since the mid-20^th century, land adjacent to the lake has been increasingly claimed for agriculture, and the surrounding wet meadows have been extensively drained. The affluent springs are exploited for irrigation, and the main inflowing channel has been canalised, with very little water now reaching the lake except after periods of intense rainfall. Groundwater pumping also occurs throughout the basin, and water is abstracted to the adjacent Skoteini polje via a tunnel constructed by the Romans. This intensive exploitation has lowered the water table, and rendered the lake susceptible to the increasing frequency and longevity of droughts driven by climate change. An extended rainless period caused the lake to completely dry out from 1989 to 1991, and this event may have led to the extirpation of the Stymphalia Chub (see 'Population'). A major fish kill affecting several species was also reported during the summer of 2017. Additional pressures include fly-tipping of domestic waste and a reduction in water quality due to leaching of agrochemicals and fertilisers from fields adjacent to the lake, both of which are driving eutrophication and the rapid extension of reed beds. The effects of pollution are also exacerbated during dry periods.

The primary threats in the Vouraikos River catchment are related to diffuse pollution from livestock farming in the middle and upper portions of the catchment, plus point-source pollution from the discharge of untreated cheese whey effluents directly into the river. Water quality in the lower part of the catchment reportedly remains high, and this has been linked to the presence of dense riparian vegetation in the Vouraikos Gorge area (see 'Conservation'). However, the river's delta has been heavily degraded for urban development, flood control and olive cultivation.

This species is not used or traded.

Both Lake Stymphalia and the Vouraimkos Gorge are protected areas, and are included in the European Union's Natura 2000 network (sites GR2530002 and GR2320003, respectively). The Stymphalia Chub is not a target species for either of these sites.

Lake Stymphalia was from 2013-2018 incorporated in the European Union co-funded LIFE-Stymphalia project (LIFE12 NAT/GR/000275), which aimed to restore wetland habitats and engage the local community in sustainable management of the lake. The native fish community was not included in any of the project's objectives, and reed-bed cutting was the primary conservation action implemented.

It is strongly recommended that future research efforts should prioritise the taxonomic identification of chubs currently inhabiting the Lake Stymphalia and Vouraikos River catchments. This could potentially be resolved by an integrated comparison of individuals collected from the lake both before and after the 1989 drying event with those from the Vouraikos, plus other Squalius subpopulations inhabiting Peloponnese river systems.