L. Forró szerk.: Miscellanea Zoologica Hungarica 10. 1995 (Budapest, 1995)

Specziár, A.; Vida, A.: Comparative study of Gymnocephalus cernuus (Linnaeus, 1758) and G. baloni Holcik and Hensel, 1974 (Pisces, Percidae)

and chironomid larvae, primarily in autumn. On the other hand, the food of G. cernuus contains more gammarids and copepods. In addition, an increasing consumption of corophiids by G. cernuus could be observed in summer, when this component was entirely lacking in G. baloni. Smaller differences were found between the two species in the Szigetköz area, although G. baloni consumed larger amounts of gastropods (Pisidium sp.) and corophiids annually, whereas gammarids dominated in G. cernuus. Similar to the results of research conducted in the Csallóköz (Nagy 1985, 1986), the food of the two species significantly differed only on the species level and in the proportion of the various components. These differences can best be explained by differences in habitat. So G. baloni inhabiting rock-fills consumes more leeches, gastropods, etc. than G cernuus, which searches for food on the open bottom. Even Holcik & Hensel (1974) presumed that the separation of the two species could possibly be explained by their ecological isolation. On the basis of the results of our investigations, we conclude that the separation of habitats was the first step within the process of ecological isolation that triggered further changes in ethology (solitary life, territorial behaviour in contrast to group-wise occurrence) and morphology (the selection of the deep-bodied G. baloni for stronger territoriality). References Aleksandrova, A. I. (1974): Morfoekologicheskaya kharakteristika ersha Acerina cernua (L.) srednego techeniya Dnepra (A contribution to the morpho-ecological characteristics of common ruffe Acerina cernua L. from the middle Dneiper). - Vop. Ikhtiol. 14: 65-72. Bagenal, T. B. (1978): Methods for assessment offish production in fresh waters. Third edition. Blackwell Scientific Publications, Oxford, London, Edinburgh, Melbourne. 365 pp. Basti, I. (1988): On the reproduction biology of three Gymnocephalus species (Pisces: Percidae). Práce Ust. Rybar. Hidrobiol. (Bratislava) 6: 9-31. Berinkey, L. (1966): Halak - Pisces. - In: Magyarország Állatvilága (Fauna Hungáriáé) 79, Akadémiai Kiadó, Budapest, 136 pp. Bíró, P. (1971): Growth investigation of ruffe (Acerina cernua L.) in Lake Balaton. - Annal. Biol. Tihany 38: 131-142. Botta, I., Keresztessy, K. & Pintér, K. (1984): Gymnocephalus baloni Holcik et Hensel, 1974 (Percidae) - a new member of Hungarian fishfauna. - Aquacultura Hungarica (Szarvas) 4: 39-42. Fedorova, G. V. & Vetkasov, S. A. (1974): Biologicheskaya kharakteristika i chislennost' ersha Acerina cernua (L.) ozera Il'men' (The biological characteristics and the abundance of Lake II'men' fishes of small value. Report I. Ruffe). - Vop. Ikhtiol. 14: 968-973. Guelmino, J. & Harka, A. (1985): Prilog prounachavanyu vste Gymnocephalus baloni Holcik et Hensel, 1974 y Tisi. - Zbornik magice srpka za prirodne nauke 69: 165-170. Harka, Á. (1984): New member in the fishfauna of the river Tisza: the Balon stickleback (Gymnoceplialus baloni Holcik & Hensel, 1974). - Tiscia (Szeged) 19: 179-182. Harka, Á. (1992a): A Dráva halai [Fishes of the river Dráva]. - Halászat 85: 9-12. Harka, Á. (1992b): A Rába halfaunája [The fishfauna of the river Rába]. - Halászat 85:154-158. Hensel, K. (1979): Geographical distribution of Pereid genera Gymnocephalus and Zingel (Osteichthyes, Percidae) in Slovakia. - Folia Zool. (Brno) 28: 85-94. Holcik, J. & Hensel, K. (1974): A new species of Gymnocephalus (Pisces, Percidae) from the Danube, with remarks on the genus. - Copeia 1974(2): 471-488. Keresztessy, K. (1993): A Börzsöny halfaunisztikai vizsgálata [Ichthyofaunistical research of the Börzsöny]. - Halászat 86: 67-68. Kolomin, Yu. (1977): Ersh Acerina cernua (L.) r. Nadym (The ruffe Acerina cernua L. of the Nadym River). - Vop. Ikhtiol. 17: 395-399.