Abstract:The current population status of the critically endangered Greek valencia Valencia letourneuxi (Sauvage, 1880), is presented, based on a thorough survey of low-altitude aquatic systems of Western Greece. The species' historical geographical range appears to have been reduced, with the westernmost and southernmost populations being currently extinct or near extinction respectively, and the remaining ones in a vulnerable state. According to univariate and multivariate analysis, V. letourneuxi exhibits habitat specificity, with a strong affinity towards spring-fed wetlands with clear waters and rich surface vegetation, being thus vulnerable to human-induced habitat modifications and hydrological changes. The impact of the above threats, as well as of the introduction of alien species such as the mosquitofish Gambusia holbrooki is discussed.

In this paper we supplement Greece's recent annotated inventory of freshwater fishes per hydrographic basin with recent distributional data and taxa alteration information, based on field sampling and a literature review up to September 2011. We report on newly documented distributional records of 31 fish species plus one unidentified taxon, within 35 hydrographic river basin units in Greece. These new records include 14 native fish species, seven alien and 12 translocated. Translocated taxa are distinguished from aliens, in order to report species non-indigenous to a basin but native within the same ecoregion. Twelve hydrographic basin units are newly added to the roster of ichthyologically explored river basins following a previous basin-scale inventory method (the total is now 117). This review increases the number of Greece's freshwater fish taxa to 167, since four new species are added to the list (Carassius langsdorfii, Neogobius fluviatilis, Telestes alfiensis, Millerigobius macrocephalus) and two are deleted (Salmo dentex, Barbus rebeli) due to taxonomic changes. Taxonomic changes will probably continue to alter the national list since phylogenetic research is ongoing on several taxa in many parts of the country.

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Valencia letourneuxi is a critically endangered freshwater fish in urgent need of targeted conservation. Little information is however available on its life history and feeding ecology; therefore, food resource utilization by V. letourneuxi was studied in its most abundant known Greek population of Chiliadou stream. The diet of this population appears to be dominated by microcrustaceans, Dipteran larvae, Acari, and Mollusca. Its feeding is highly dependent on seasonal prey availability and diversity, with niche overlap being low only between winter and the rest of the seasons, indicating that only during winter its diet differs significantly in relation to the other seasons. There are no significant sex-and sizerelated dietary shifts. This V. letourneuxi population is characterized by a generalist feeding strategy and appears to consist mostly of individuals with broad niches. Its generalist feeding pattern and dietary flexibility permits it to fully exploit this very diverse and rich habitat and may account for the high local abundance of this population.

Changes in lotic benthic macroinvertebrate assemblages along the transboundary Axios-Vardar River (Greece -Former Yugoslavian Republic of Macedonia) were examined in order to identify major anthropogenic impacts correlated to the benthic community composition during the low flow season. Macrozoobenthos and water samples were collected from 21 sites during summer 2000 and beginning of autumn 2001. Parallel to sampling, the recording of the physical structure of the sites took place using the River Habitat Survey (RHS) method. The multivariate techniques of FUZZY and Canonical Correspondence Analysis (CCA), as well as the Hellenic biotic score (HES) and the habitat quality scores (HMS, HQA) were applied to the data. Total dissolved solids and total suspended solids were found to be the primary factors affecting the structure of the observed communities. Additionally, species composition responded to anthropogenic activities, e. g. untreated sewage effluents, industrial discharges, agricultural runoff, intense water abstraction and impoundment. As expected, macrozoobenthos community composition shifted from sensitive to tolerant taxa where human impacts were most evident.