The occurrence of common gudgeon in the River Morača drainage of southern Montenegro was investigated. Low numbers of specimens were recorded in four out of five localities investigated on the Zeta River and at a single locality on the lower part of the River Morača. Allozyme analysis revealed that the specimens examined belong to the species Gobio gobio (Linnaeus, 1758). The lower number of lateral line scales in common gudgeon from the Ohrid-Drim-Skadar system, as compared with other European populations, probably indicates clinal variability. The results also demonstrate that the subspecies Gobio gobio ohridanus Karaman, 1924 is not a valid taxon.
In Slovakia, Cobitis elongatoides (Bacescu et Mayer, 1969), Sabanejewia balcanica (Karaman, 1922), and Misgurnus fossilis (Linnaeus, 1758) are protected by national legislative, and localities of European importance have been delimited for these species within the Natura 2000 system. In Slovakia, the three species only occur in the Black Sea river system (the Danube and Tisza R. basin). Of them, C. elongatoides is the most widely distributed and most numerous both in its pure form and its hybrid, diploid-polyploid complexes (C. elongatoides x C. tanaitica). It occurs in proper streams and in natural as well as in artificial aquatic habitats, above all, in lowland regions. Comparing data on this species from 1955–1965, no major changes have been found. S. balcanica occurs chiefly in the middle reaches of rivers, first of all, in the Bodrog drainage area (the Laborec, Ondava, Topľa R.) in eastern Slovakia. In the western part of Slovakia (the Danube river system) the occurrence of this species is distinctly less frequent and insular. The distribution of the species has been markedly affected by water pollution, construction of dams and reservoirs, and river bed modifications. The occurrence of M. fossilis is almost exclusively limited to the lowland regions of eastern Slovakia and the Danube Lowland. In those regions, the amelioration measures taken during the second part of the 20th century caused the original natural wetlands to vanish – together with the occurrence of this species. However, M. fossilis found a secondary suitable environment in man-made hydro-amelioration channels, earth pits, and fishponds.
Almost after a century, the occurrence of Zingel streber (Siebold, 1863) was recorded again in the area of confluence of the rivers Morava and Dyje. The population consisted of fish 0+ to 5+, with 0+ group predominating in the sample, indicating that the species had successfully reproduced in 2003. Analysis was made of their karyotype (n=5) and meristic characters (n=10). The following was the result of a study of growth of standard lengths (n=16): SL1 – 81 mm, SL2 – 114 mm, SL3 – 130 mm, SL4 – 146 mm, SL5 – 166 mm. The biggest individual was a female 5+ of age, TL 200 mm, SL 180 mm. The habitat types preferred by individuals 0+ were the rapidly flowing sections with gravel bottom, in which the stream velocity was 0.2–0.6 m.s-1. Re-occurrence of this species was facilitated by the marked improvement of water quality after 1990 as well as by the barrier-free connection of sections of the rivers Morava and Dyje with the Danube via the Slovakian-Austrian part of the River Morava. Further dispersal of this species is limited by the weir in r.km 26.7 on the Dyje, and six weirs between r.km 74.1 and r.km 101.8 on the Morava. Z. streber is protected by national law and the area mentioned above has been proposed as a pSCI for the NATURA 2000 system.
Four lamprey species and 55 fish species are considered autochthonous taxa in the Czech Republic. In recent years, as a result of spontaneous migrations, the native ichthyofauna has been increased by three species Sander volgensis, Gymnocephalus baloni, Proterorhinus marmoratus) which, in view of their autochthonous occurrence in the Central European region, are evaluated as native. At present, according to the criteria of the IUCN (2001) version 3.1, two lamprey species and 6 fish species are evaluated as “regionally extinct”. Most of these taxons are denoted as anadromous. One species has been classified in the category “Extinct in the wild”. Two lamprey species and 25 fish species are considered to be endangered to various extent: one lamprey species and 10 fish species are classified as “Critically endangered”; one lamprey species and 5 fish species as “Endangered”; ten fish species as “Vulnerable”. In the course of the past two centuries, attempts have been made at introducing about 30 fish species (see Lusk et al. 1998, Hanel 2003); of these, the introduction of 11 species can be evaluated as successful. Only four non-native species have established stable and naturally reproducing populations in natural conditions (Pseudorasbora parva, Carassius auratus, Ameiurus nebulosus, Gasterosteus aculeatus).