38th IAD Conference, June 2010, Dresden, Germany 1 Long-term changes of fish fauna in the Hungarian section of the Ipel River ANDRÁS WEIPERTH, TIBOR GAEBELE, IMRE POTYÓ, GÁBOR GUTI 1 Keywords: historical fish fauna, species richness, invasive species, natural reference, river restoration 1 Introduction Rivers have long been affected by several types of human influences that have a negative impact on their integrity. Nowadays, improvement of ecological status of a river system is an increasing demand of the society but the delineation of the environmental objectives for rehabilitation is often restricted by a lack of knowledge of pristine conditions. The possibilities of direct investigation of undisturbed rivers are very limited; therefore, historical information from the pre-regulation period can be used for describing the original state. Due to their complex habitat requirements fish are sensitive indicators for the ecological integrity of a river (Karr 1991) and long-term changes of fish fauna can be reconstructed from old catch records, data of early publications and habitat descriptions from archive maps (Carrel 2002, Wolter et al. 2005, Winter et al. 2008). The Ipel is a medium size regulated river along the border of Hungary and Slovakia. Its source is at 1020 m above sea level in Slovakia and its tributary is at Szob at rkm 1708 of the Danube. The length of the river is 257.4 km, its catchment area is 5108 km 2 and its mean discharge is 20.6 m 3 s -1 . Its flow regime fluctuates between 1.7 m 3 s -1 and 660 m 3 s -1 . The first efforts of river regulation are known from the 17 th and 18 th century. Some meanders were cut off and several small tributaries were regulated in the 19 th century. In the 1980s, six dams were constructed between Ipolytölgyes and Sahy (Mike 1991, Kabay 2007). The interventions resulted in channel incision and a decrease of mean and low water levels. The lower section of the river belongs to the Danube-Ipel National Park and an increasing effort is made to restore its ecosystem in the recent years. Our study was aimed to assess the deviation of the present fish fauna from its original reference state in the Hungarian section of the river. Analysis of ichthyologic literature and history of river regulation provided information for the judgement of former fish fauna. 2 Methods The long-term changes of the fish fauna and occurrence of species were evaluated by literature data. Acceptable reports are available from the end of the 19 th century (Herman 1887, Vutskits 1918, Vásárhelyi 1961, Kux & Weisz 1964, Botta et al. 1984, Botta 1993, Keresztessy 1993, Györe et al. 2001, Tóth et al. 2005). The description of the recent fish fauna was completed by the results of our fish surveys undertaken by electrofishing in the vicinity of Ipolytölgyes (rkm 18) and Szob (rkm 2) between July and October 2009. 3 Results Our fish surveys detected 38 fish species and three of them (Ameiurus melas, Neogobius melanostomus, Neogobius gymnotrachelus) were new for the Ipel. According to results of literature analysis and data of our fish surveys the occurrence of 56 fish species has been proved in the Hungarian section of the river (sequence according to Table 1): 1 Hungarian Danube Research Station of the H.A.S., H-2131 Göd, P.box 8. Hungary. e-mail guti.g@t-online.hu