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
Side branch systems in the flood-plain The side branch systems of the flood-plain are located at the meeting points of various biogeographical zones. They are characterized by a great diversity of habitats. Not only the species native here, but also those occurring in the main channel or migrating from large distances (several hundred kilometres) spawn regularly in this area. Therefore the species number (n=52) is very high. The loss of the side arm systems will thus negatively affect the fish fauna of the Danube itself downstream the Szigetköz area. The existence of a connection between the various water types could have guaranteed the conservation of the fishfaunistic values found in this area. However, water disappeared from most of the side arm systems in the flood-plain. The fish fauna found its way to the main channel, where even the most elementary conditions are lacking for the survival of the species characterizing the side branches (e.g. Esox lucius, Cyprinus carpio, Scardinius erythrophthalmus, Abramis sapa, Leuciscus idus, Tinea tinea, Perca ßuviatilis). This is also critical that the fish could not acquire the body condition necessary for hibernation, as their intensive feeding was impossible at the time of the diverting. The required amount and quality of food was lacking in the main channel all over. Those species that already started hibernating, became stuck to the few remaining water bodies and were eventually eliminated due to continuing habitat loss or the intense "activities" of fishermen. The inundation that arrived at the end of November 1992, filled up the side-branches again with water, but could not sufficiently change the situation. The individuals that survived settled again in the side-arms, but after the inundation was stopped their habitats disappeared. The level in the water bodies of the flood-plain has slowly reached that of the ground water, and will continually follow its fall. In the period following the divertion of the Danube, some of the water bodies freezed to their bottoms several times. The fish that were forced to hibernate here could not survive the winter. Even those that were stuck to deeper parts had insufficient condition for hibernation, and their survival chance is very questionable. Species probably disappeared in the past few months: Eudontomyzon mariae, Salmo trutta m. fario, Gobio kessleri, Pelecus cultratus, Cobitis aurata, Cottus gobio, Gymnocephalus schraetzer. Species expected to disappear within a few years: Acipenser ruthenus, Cyprinus carpio m. hungaricus, Gobio albipinnatus, Leuciscus leuciscus, Rutilus pigus virgo, Lota lota, Gymnocephalus baloni Species expected to suffer serious population decline: Anguilla anguilla, Cyprinus carpio, Abramis brama, A. ballerus, A. sapa, Aspius aspius, Barbus barbus, Blicca bjoerkna, Chondrostoma nasus, Ctenopharyngodon idella, Gobio gobio, Hypophthalmichthys molitrix, H. nobilis, Leuciscus cephalus, L. idus, Vimba vimba, Cobitis taenia, Noemacheilus barbatulus, Silurus glanis, Gymnocephalus cernuus, Stizostedion lucioperca, S. volgense. 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: Umbra krameri (occurrence not verified by specimens), Esox lucius, Alburnus alburnus, Carassius carassius, C. auratus, Leucaspius delineatus, Pseudorasbora parva, Rhodeus sericeus amarus, Rutilus rutilus, Scardinius erythrophthalmus, Tinea tinea, Misgumus fossilis, Ictalurus nebulosus, Lepomis gibbosus, Perca ßuviatilis, Proterorhinus marmoratus.
