L. Forró szerk.: Miscellanea Zoologica Hungarica 8. 1993 (Budapest, 1993)
Vida, A.: Threatened fishes of the Szigetköz
Experimental fishing in all water types took place in every season annually, from 1986 to 1993, with a total of 187 collecting days. Number of sampling localities according to the different hydrogeographical categories: - main channel, 14 sampling points; - flood plain, 120 sampling points; - irrigation channels outside of the flood plain, 8 sampling points; - backwaters of the flood free area, 12 sampling points; - ponds of gravel-pits; no sample; ' ::;. ,—r\„. - Mosoni-Duna, 6 sampling points. <&^'"_ '&d~^ T-\ Fig. 1. Location of the Szigetköz Results The area has been classified by Balon (1964) as a "sub-montane zone". He studied the fish fauna of this zone thoroughly, including all branches of the river. His ecological categories are based on both physical (e.g. water current) and biotic (fish fauna) characteristics. In his opinion, the "sub-montane" zone extends between 2000 and 1650 riverkilometers. The Szigetköz section of the river ranges from 1850 to 1794 riverkms. Holfcik et al. (1981) published hydrobiological and ichthyological investigations in connection with the planned GabCikovo-Nagymaros hydroelectric power system. They listed 66 fish species from the Slovakian side of Danube, from which 4 can be denied for various reasons: - Eudontomyzon vladykovi is identical (synonymous) with Eudontomyzon danfordi, also included in the list; - Barbus meridionalis petényi, which can only be found west of the DanubeBend (Visegrád-Esztergom) in "Pilis-Hills"; - Salvelinus fontinalis and - Micropterus salmoides which have not been found in the last 20 years. For similar reasons the presence of Acipenser gueldenstaedti in this area seems to be dubious, though its accidental occurrence in the future cannot be excluded. Eventhough the area is included in this species' range on the distribution map published by Vlasenko et al. (1989), they indicate that no records are known since 1902. The study of the Hungarian side (Jancsó & Tóth 1987) gave a list of all indigenous species of Acipenseridae, including very early literature data. Micropterus
