Over the past 150 years, the waters of the Czech Republic were experimentally stocked or invaded by a total of 41 alien (non-native) fish species. The following species have become fully naturalized and produced self-sustained populations: Carassius gibelio, Pseudorasbora parva, Ameiurus nebulosus and Gasterosteus aculeatus, which produced stable populations in several spatially limited localities. In some cases Oncorhynchus mykiss, Salvelinus fontinalis and Coregonus maraena will produce instable temporary populations based on released material obtained from fish farms and ponds. The occurrence of the remaining acclimatized alien species (Coregonus peled, Ctenopharyngodon idella, Hypophthalmichthys molitrix, Aristichthys nobilis) in natural ecosystems and fishponds depends on stocking fish obtained from artificial spawning and cultures. The documented annual average production of alien species fit for human consumption amounts to around 2 000 tonnes, i.e. 8.2 % of the annual average production of marketable fish cultures in the Czech Republic. A significant negative impact of the introduced species on native ichthyofauna has been ascertained as regards its ecological, biological properties, biodiversity and health. Considered a typical invasive alien species, Carassius gibelio heavily depressed the occurrence and numbers of indigenous Carassius carassius populations and also contributed to the decreased numbers of Tinca tinca, Leucaspius delineatus and other native cyprinid fish. P. parva and A. nebulosus show a much weaker and limited impact. The introduction of C. idella was accompanied by the introduction of the tapeworm species, Bothriocephalus gowkongensis, which subsequently caused heavy losses in cultures of Cyprinus carpio. In 2008, Neogobius melanostomus was recorded for the first time in this country at the confluence of the Morava and Dyje rivers.
The population and genetic profiles of a remnant Vimba vimba population in the upper course of the River Dyje (N=48°53 ́18 ́ ́/ E=15°39 ́29 ́ ́) was carried out to provide a basis for conservation measures. This population is an isolated fragment of a more widespread population in this river system and is now declining. It came into being 60 years ago as a consequence of the construction of the Vranov dam in the middle section of the River Dyje. Over those 60 years V. vimba disappeared from the other localities of the River Dyje basin. In the population under study, vimba is a single-batch spawner involving two age groups of fishes (4 to 5 years of the age). Individuals over six years of age are rare and sporadically occurring fishes of 8 to 10 years are exclusively females. The size of the adult part of population is less than one thousand individuals. The length growth rate is relatively high as compared with other studied populations in the Czech Republic, fishes of five years attain 200 mm of Sl. A very low genetic variability was evidenced in the population (mean number of alleles per locus = 1.30 ± 0.1; percentage of polymorphic loci = 16.7 %; mean observed heterozygosity = 0.022 ± 0.011).
RAPD-PCR method is now widely employed in genetic research and is a powerful asset when trying to identify species. In the present work, RAPD genetic markers were obtained for distinguishing between three species of the genus Gobio that show substantial morphological resemblance. Different profiles were observed: six species-specific markers were detected for G. gobio, four for G. kesslerii and nine for G. uranoscopus. These markers were reproducible, dependable and very helpful in differentiating between these species.
Thee species of the genus Gobio occur in the hydrographical network of the Czech Republic, belonging to the basins of three seas (the North, black, and Baltic seas). G. Gobio is distributed over streams belonging to all three sea basins. It is most common in their middle reaches, which are inhabited by fish communities of the Barbus-Chondrostoma type. Compared to that past, the population numbers of this species have not undergone any marked changes. G. kesslerii occurs only in the Bečva River (a tributary to the Morava River) and in the Morava River upstream of the mouth of the Bečva River (danube basin, Black Sea). G. albipinnatus is distributed over the Morava and Dyje rivers and their tributaries (Danube basin, Black Sea). Compared to a century ago, the extent of distribution of G. albipinnatus has dropped to about 50%, which is due chiefly to stream canalisation and water pollution. At present, G. albipinnatus has been ascertained in the lower part of the River Labe, yet there are some doubts as to the originality of this occurrence. The localities of G. albipinnatus and/or G. kesslerii are shared with G. Gobio, with which they hybridise. No evidence is available of the occurrence of G. uranoscopus (Agassiz, 1828) in the Czech Republic, although it does occur in neighbouring Slovakia and Austria. The most important devastation factors, which limited the distribution of the gudgeon in the past, include the construction and operation of dams and weirs, stream canalisation and water pollution. National laws project G. kesslerii as critically endangered and G. albipinnatus as endangered. Both species are listed in European conservation laws (Council Directive no. 92/43/EEC) and, therefore, special areas of conservation have been delimited for them within the NATURA 2000 system.
The following species of the genus Gobio occur in the Tisza River drainage area in Slovakia: G. Gobio, G. kesslerii, G. albipinnatus and G. uranoscopus. G. Gobio is the commonly distributed species. It occurs in streams of various sizes, attaining the largest numbers in streams populated by the barbel type fish communities. It occurs together with other Gobio spp., whith which it can produce hybrids. The present occurrence of G. Gobio has not changed basically from that in the past. G. albipinnatus occurs primarily in lowland streams, both in large rivers and canalised minor streams and channels. The distribution of this species in the Tisza River drainage area in Slovakia has not, appreciably changed from that in the previous period. According to earlier data, G. kesslerii was relatively abundant in the middle and upper reaches of a number of streams. At present the occurrence of this species has been confirmed in just a few localities so that its range has been markedly restricted. In some cases, however, the species may have been mistaken for G. albipinnatus. According to literary data, G. uranoscopus occurred in the past mainly in the upper reaches of rivers Torysa (the Hornád River drainage area), Topľa, Ondava, Laborec, and Uh (the Bodrog River drainage area). This species shows the most marked decrease in range, compared to that in the past. in recent times its presence has been confirmed only in a few localities. The devastating factors that have affected the distribution of the particular Gobio spp. include water pollution, stream and bed canalisation, decreased river bottom diversity, extraction of gravel materials, and hydro-energetic constructions (steps, weirs and dams). of the above gedgeon species, G. uranoscopus and G. kesslerii are protected by the national legislation in Slovakia. In accordance with the EU legislation (Council Directive 92/43/EEC), special protection regions (NATURA 2000) are being defined for G. uranoscopus, G. albipinnatus, and G. kesslerii.
The Amur sleeper, Perccottus glenii Dybowski, 1877, is indigenous in eastern Asia. During the second half of the 20th century, with the aid of man, it spread over the eastern part of Europe as well as in central Asia. In the course of 50 years of its dispersal in the western direction the species already reached the Vistula drainage area (the Baltic Sea basin) and the Danube drainage area (the Black Sea basin). In the latter basin, its occurrence was ascertained in the drainage area of the Tisza river in Hungary in 1997. In eastern Slovakia, the Amur sleeper was first recorded in 1998 in the Latorica drainage area. In the course of subsequent years it has become a common species in the streams in the basins of the Latorica, Bodrog and Tisza rivers. In shallow lentic waters densely grown with aquatic plants the species becomes a superdominant or even exclusive species in the local fish communities. It has no marketable value but presents a serious threat to the existence of native fish species with similar identical microhabitat requirements.
Seven populations (Oľšava/Hornád R., Oľšava/Topľa R., Ublianka R., Ondava R., Ipeľ R., Malý Dunaj R. and Vlára R.) of Balcan spined loach were subjected to phylogenetic analysis based on variability of the cytochrome b gene and mitochondrial specific marker. They were separated in to five groups but these groups were represented by specimens from different populations. Genetic distances among populations and among groups were quite low. Subsequently, analysis of relations among our groups and sublineages of Danubian-Balkanian complex of Sabanejewia was made. the first four groups were genetically close to sublineage III, while the fifth one to the sublineage IV. These findings agree with the conclusion about conspecificity of analysed Danubian-Dniester populations belonged to monotypic S. balcanica. Phylogenetic analysis showed that the most suitable populations for the restoration of this species in the Bečva River are populations dwelling the Ipeľ and Vlára rivers.
Genetic diversity of three pure populations of Cobitis elongatoides from hydrologically and geographically different drainage areas, the Lužnice River (48.49.60 N, 14.55.60 E, Labe River drainage area, North Sea basin), the Nová Říše reservoir (49.09.11 N, 15.32.464 E, Morava River drainage area, Black Sea basin), and the Ida River (48.32.284 N, 21.03.421 E, Tisza River drainage area, Black Sea basin) was evaluated by sequencing of mitochondrial cytochrome b gene. Species identification of unknown Cobitis samples from Vipava River drainage area in Slovenia was also performed based on cytochrome b sequence. All forms of the genus Cobitis are protected by national legislatives and, in accordance with the Council Directive No. 925/43/EEC, they enjoy protection in selected localities of European importance. In total, 11 haplotypes of Cobitis elongatoides were found in Czech and Slovak waters, manifesting low overall genetic diversity. Samples from Vipava River drainage area were identified as Cobitis bilineata.
The random amplified polymorphic DNA (RAPD) method was applied to eight Gobio gobio populations living in the rivers of the Czech Republic and Slovakia. The application of seven RAPD primers yielded eight fingerprint characteristics for the populations examined. Forty diagnostic markers have been identified, which can reliably identify the populations under study. Intrapopulation diversity varied between 0.26 and 0.38. A phenogram documented the close agreement of the particular populations with the geographic pertinence of their localities to the different sea basins.
Sample of Gobio gobio from 30 localities in the Czech Republic and Slovak Republic were studied. Starch gel electrophoresis was used for evaluation of variability of allozyme patterns in 16 active protein systems comprising 26 loci. Products of 17 loci were considered to study the genetic structure of its populations. From this, genetic variability was found in ten loci, occurrence of rare alleles was detected in next four loci. Percentage of polymorphic loci ranged between 6 and 41%; mean occurrence of alleles was between 1.1 and 2.0 per locus; and mean heterozygosity was observed at 0.013 to 0.248. The genetic distances among populations were 0.002 to 0.175 (N e i 1972) and 0.063 to 0.385 (C a v a l l i - S f o r z a & E d w a r d s 1967). Differences in occurrence and frequencies of alleles in some loci among the sea basins were evident. Higher genetic variability identified in populations from the Danube river system (Black See basin) is probably connected with the fact that this basin served as a refuge for ichthyofauna during glaciations.