L. Forró szerk.: Miscellanea Zoologica Hungarica 8. 1993 (Budapest, 1993)

Vida, A.: Expected effects of the Gabčikovo river barrage system on the ichthyofauna of the Szigetköz and its values

Qualification of the disconnected backwaters and the expected changes according to the number of valuable fish species are given in Fig. 3. Irrigation canals The regulation of the main channel in the last century affected the whole water system of the Szigetköz. At the time of inundation in the Danube, springs occurred in a broad zone on the disconnected side. For this reason, between 1896 and 1900 irrigation canals were built, the system of which has a length of approximately 300 km today. During their construction old and dry Danube basins were used, but generally their banks are mostly straight, regular. They are regularly cleaned, and thus have open water surface. Interesting areas from the ichthyofaunistical point of view could only develop at natural and artificial obstacles (bridges, trees fallen into the water, meanders) and in weedy parts. The species Gobio albipinnatus and Umbra krameri deserve particular interest, both being protected and endangered in Hungary (and on the European level as well, Lelek 1987). Due to the diverting, the water level in the canals fell significantly, their flow was reduced or they became stagnant. For this reason, the status of the rheophilous species became critical. As the effects of the interaction are delayed due to the exclusive contacts with the ground water, the ultimate results will be evident only months later. Species probably disappeared in the past few months: Eudontomyzon mariae, Cyprinus carpio, Leuciscus leuciscus, Ictalurus nebulosus. Species expected to disappear within a few years: Esox lucius, Umbra krameri, Blicca bjoerkna, Carassius auratus, Gobio albipinnatus. Species expected to suffer serious population decline: Alburnus alburnus, Ctenopharyngodon idella, Gobio gobio, Leuciscus cephalus, L. idus, Rutilus rutilus, Cobitis taenia, Noemacheilus barbatulus, Perca fluviatilis. Some of these species are positively affected, but are included in this list due to habitat loss. Species expected to be indifferent as regards to these changes: Carassius carassius, Leucaspius delineatus, Pseudorasbora parva, Rhodeus sericeus amarus, Scardinius erythrophthalmus, Tinea tinea, Misgurnus fossilis, Lepomis gibbosus, Proterorhinus marmoratus. Fig 4. Qualification of the irrigation canals and the expected effects according to the number of valuable fish species.