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Artificial propagation and stocking of brown trout is a standard practice in recreational fishery management. In recent decades, the importance of maintaining intraspecific diversity and protecting locally adapted lineages has been recognized for the species' long-term survival. The first step in selecting donors for stocking involves distinguishing native trout from non-native and introgressed individuals. The established method for discerning Atlantic hatchery strains from the wild populations involves genetic screening of individual diagnostic SNPs and microsatellite assignment tests. This study, using Serbia's Panjica hatchery as an example, illustrates the proper conduct of routine genetic screening for identifying suitable donors for supportive stocking. The broodstock and reference populations were screened using mtDNA control region, LDH nuclear gene, and 12 microsatellite loci to assess the origin, diversity, and inbreeding levels. The analysis revealed only moderate contamination with Atlantic trout and showed the regional origin of the Danubian genes – over 50% of the broodstock was composed of non-introgressed Danubian individuals tracing their origin to the Zapadna Morava River system. Additionally, the study highlighted a considerable discordance between LDH locus and microsatellites in identifying introgressed individuals, raising concerns about the sole reliance on LDH locus for the identification of Atlantic genetic origin in nuclear DNA.

The southernmost part of Albania, the Butrinti Lake area is characterised by a highly diverse freshwater fish community with a high degree of regional endemism. This study focuses on the Corfu killifish (or toothcarp) Valencia letourneuxi (Sauvage, 1880) that is endemic to the western part of the Ionian Ecoregion, and reported in Albania in the past from a single location, Lake Butrinti. Recently, in June 2019, the species has been rediscovered at a very low population density (only 11 individuals collected) in a spring-fed stream in the vicinity of Lake Butrinti. Other fish present together with V. letourneuxi were the native Telestes pleurobipunctatus, Barbus peloponnesius, Anguilla anguilla and Pelasgus thesproticus and the translocated Alburnus sp. Our findings provide useful insights into the ecology and conservation of a Critically Endangered, range-restricted species and its habitats. The Corfu killifish presence correlated negatively with water depth and positively with aquatic vegetation coverage. The conservation implications of our findings both for the target species and the co-occurring fish fauna in its spring-fed habitats are discussed.

Pelasgus Kottelat & Freyhof 2007 (Leuciscidae) is a freshwater fish genus endemic to the Southern Balkans. The distribution of most of its species is insufficiently known. Pelasgus was molecularly studied only marginally, and the genetic diversity of individual species or populations, crucial for their conservation, is completely unknown. We studied distribution and genetic diversity of Pelasgus stymphalicus (Valenciennes 1844) and Pelasgus marathonicus (Vinciguerra 1921), two widespread species from southern Greece. Our data, based on cytochrome b sequences, confirmed that a number of populations whose taxonomic status had been uncertain, belong to one of these species. The distribution range of P. stymphalicus includes the Ionian mainland, from the Acheloos to Mornos rivers, and most of the Peloponnese, excluding the Evrotas and the headwaters of Alfios. The native range of Pelasgus marathonicus is the western Aegean mainland, from rivers near Athens to the Xerias river in the Pagasitikos Gulf. AMOVA showed that the genetic variance is slightly higher among than between populations. High FST values indicated a pronounced genetic differentiation of the populations in both species. There was a high proportion of private haplotypes and a very small number of shared haplotypes between populations in both species, which indicates uniqueness of each population and their susceptibility to human-induced changes.

Fish assemblages and their distributions in the western Balkan rivers have rarely been investigated. This study provides initial insights into the spatial patterns of fish distributions in the main-stem of the White Drin in Kosovo. Sampling primarily utilized back-pack electrofishing at 11 sites along the river's entire main stem, recording 21 species. Identification of most fish species was confirmed through DNA barcode analyses; two yet unnamed species are present and some taxonomic problems were discovered. The abundance of non-native species was low (5.9% of the catch) but seven of the eight non-natives have established populations. A longitudinal fish zonation pattern was described for the first time in this river; fish assemblages in an upstream-to-downstream gradient were characterized by a decrease of cold-water species (salmonids, minnows) and an increase of large-river cyprinids and non-native species. Multivariate ordination and network analyses demarcate preliminary fish assemblage types and specific environmental and anthropogenic pressure attributes are shown to influence assemblage structure. Natural assemblage patterns may be locally disrupted by anthropogenic pressures such as pollution and hydromorphological disturbances, however most sites show semi-natural features and conditions. Recommendations for conservation and further research are provided.

Three populations of brook trout, Salvelinus fontinalis, established in streams and reservoirs in the Jizerské Mountains, Czech Republic, were studied between 1995 and 2006. The maximum age was usually 3+ to 4+, but the age 7+ was also recorded. The inflows of all reservoirs are populated mostly by 0+ to 2+ brook trout, while older specimens live in a lentic environment, migrating to lotic habitats only to spawn. The density of brook trout in streams ranged from 8 to 95 individuals per 100 m2 during spring and summer, while that for reservoirs ranged between 31 and 290 individuals per ha. A strong negative correlation between the size of adult fish and population density in reservoirs was observed. The type of management influenced both density and growth of brook trout. Further introduction of this species in the central European area should be restricted to habitats where native salmonids cannot survive, such as acidified waters.

Northern Mediterranean region is characterised by an exceptional richness of the freshwater ichthyofauna. Many fish species of this region are endemic to a single or a few river basins. This is also the case of the Neretva river basin (Adriatic Sea slope), where 17 out of 34 native species are endemic solely to this river basin. However, these unique Mediterranean freshwater ecosystems are fragile and are susceptible to human-induced changes, including introduction of alien fish species. We report here a finding of the 32nd alien fish species in the Neretva river basin, spirlin Alburnoides sp., which was found at two localities in Bosnia and Herzegovina. The spirlin species was identified by molecular means as so far unnamed species with the native range in the Sava river basin (Danube river basin, Black Sea slope). Based on the comparison of cytochrome b sequences, the introduced population originated most probably from nearby rivers of the Danube basin in Bosnia and Herzegovina (Vrbas and Bosna river basins). Such a high number of alien fish species reported in a single river basin is alarming and pointing to a necessity of raising public awareness, especially among local fishermen.

The knowledge on the distribution of native and non-native crayfish species in Europe has substantially advanced during last two decades. However, data on the exact distribution of European crayfish are still lacking in some regions of the Balkan Peninsula, e.g., in Albania. Out of five European crayfish taxa, Astacus astacus and Austropotamobius torrentium are considered to occur in Albanian freshwaters. However, until now the only confirmed localities of the occurrence of any crayfish species in Albania are a single place in the Mat River drainage and Prespa Lake. Five crayfish individuals have been collected recently from two localities in Albania: Ohrid Lake and upper Devolli River (Seman basin), as a result of a repeated sampling in all main Albanian river drainages. All specimens were morphologically and molecularly identified as the noble crayfish, A. astacus, providing confirmation of its presence in this Balkan country. The present paper summarizes historic and current distribution records of the crayfishes in Albania and neighbouring countries as well as provides insight into genetic variability of Albanian A. astacus.

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Despite being one of the most speciose fish families in the Mediterranean Sea, knowledge about the diversity of gobies (Actinopterygii: Gobiidae) in this sea is still unsatisfactory, as documented by recent descriptions of a number of new species. Although very common in shallow water, Gobius incognitus Kovačić & Šanda, 2016, had escaped attention until 2016, when it was discovered. Due to its overall superficial morphological similarity, G. incognitus used to be confused with a much rarer species, Gobius bucchichi Steindachner, 1870, which was considered one of the most common shallow-water gobies in the Mediterranean Sea. In this work, we tested the suitability of the genetic data (mitochondrial gene encoding cytochrome b) for identifying and distinguishing between these two goby species, and assessed the congruency between the distribution records based on genetic data and those based on morphological identification. We analysed material of 304 specimens of G. incognitus and G. bucchichi from 49 localities covering a considerable part of the Mediterranean Sea, Black Sea, and the Atlantic Ocean near Gibraltar, representing 19 geographically well-separated areas. We detected 270 sequences of G. incognitus, and only 34 of G. bucchichi. In both species, a high haplotype variability was observed. The sequence species identity matched morphological identification for all specimens for which vouchers were available. The mean uncorrected p-distance between G. incognitus and G. bucchichi was 13%, while the mean intraspecific distances were much lower (0.63% and 0.68%, respectively). We found 79 fixed mutations between these two species. Data on distribution based on genetic identification are completely congruent with published results based on morphological identification. The results of this study support molecular methods as a reliable tool for distinguishing morphologically similar fish species, which is particularly useful when only tissue is available for determination. [ABSTRACT FROM AUTHOR]

There is a significant gap in our knowledge of the intraspecific morphological variability in freshwater fish, although such data are crucial for understanding species diversity. Here we use the killifish Aphaniops stoliczkanus (Day, 1872; Aphaniidae: Cyprinodontiformes), which is a widespread but poorly known freshwater species in the Middle East, to investigate variability in morphological traits within and between its populations. As otolith morphology is known to evolve on ecological timescales and can signal the presence of cryptic lineages, a special focus lies on otolith variability. Based on samples from six populations in northern Oman, we found that variation in pigmentation, disparities in body shape and otolith variability can be associated with distinctive environmental conditions. The unique otolith shape of A. stoliczkanus from a hot sulphuric spring (Nakhal) suggests that a cryptic lineage may have emerged there. Our new data can serve as a benchmark for future studies on the diversity of Aphaniops and other Aphaniidae and help to clarify whether cryptic diversity is present in some lineages. Moreover, our data can serve as an actualistic model for studies on fossil fishes, in which morphological characters provide the only accessible data source for taxonomic and phylogenetic interpretations. [ABSTRACT FROM AUTHOR]