A Debreceni Déri Múzeum Évkönyve 2000-2001 (Debrecen, 2001)

Természettudomány - Juhász Lajos–Sallai Zoltán: The Fish-fauna of South-Nyírség

Lajos Juhász-Zoltán Sallai THE FISH-FAUNA OF SOUTH-NYÍRSÉG We have been examining the water habitats of Nyírség between 1998 and 1999. In the course of these two years we sampled 17 places and caught approximately 5,000 fish. We demontrated the presence of 25 species of fish and of one hybrid. For this publication we have also used our data that we had collected between 1980 and 1997. We also measured the water-quality parameters of the water habitats occasionally. From the 25 species found 6 are protected by law. Among the populations of these protected species, we have found stable ones : those of the Sunbleak, of the Mud loach, and of the Spined loach. The fish-fauna of the region is endangered mostly by drought, although in the previous years it was counterbalanced-to a certain extent-by inland waters. It is widely known that inland waters have favourable effects on water-diversity, therefore examinatons ought to be continued in order to investigate which new species have appeared in the fauna of Nyírség. It would also be important for quasi-natural waters to be populated by fish, as it may determine the fish-fauna of the given water habitat along with that of the canals connected with it. On the basis of our examinations carried out so far, it can be concluded that the fish-fauna of South-Nyírség consists of most variably composed and ecologically extremely instable associations, as a result of the small extension of water habitats, of artificially created habitats and of the rluctuality of water supply. Only a few, non- aboriginal species, which are most adaptable (and partly utilized in fishing) are able to establish stable populations and to breed. The fact that we have demonstrated only 25 species in this poorly watered region indicates that besides natural expansion and repopulation, fish-fauna is determined by populating by men. Drying out of water habitats may lead to the disappearance of almost the total fish-fauna. Therefore, control of the water in water habitats, wise use of water and restricting or stopping of populating of non-local species may result in the survival and in the protection of the ecologically important species and of their associations in Nyírség-Erdőspuszta. 45