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)

MISCELLANEA ZOOLOGICA HUNGARICA Tomus 10. 1995 p. 103-116 Comparative study of Gymnocephalus cernuus (Linnaeus, 1758) and G. baloni Holcik & Hensel, 1974 (Pisces, Percidae) by A. Specziár and A. Vida (Received June 26, 1995) Abstract: In the comparative study of Gymnocephalus cernuus and G. baloni we searched for differences in growth, habitat and feeding between the two species in support of their distinctness. Significant differences were found in both habitat and feeding, whereas growth was more or less similar. G. baloni is bound to hiding places located in flowing water. In vegetative periods it occurs solitary and in generative in pairs. G. cernuus lives in shoals in the whole season, occurring mostly in the open, still parts of waters near to the bottom. The food of the two ruffe species mostly consists of the characteristic macroinvertebrates of their habitat. The body pattern, the number of opercular spines and the cut on the membrane between AI and All were found to be the most useful characters in identification. Key words: Pisces: Percidae: Gymnocephalus cernuus, Gymnocephalus baloni; morphology, habitat, growth, feeding Introduction In 1974, Holcik and Hensel described a new species of pereid fish, Gymnocephalus baloni, from the Slovakian section of the Danube. According to the first record, this species has been treated in the literature and scientific collections as conspecific with G. cernuus, which it greatly resembles. Although no publication is known to us actually questioning the validity of G. baloni, its specific distinction is not definitely accepted despite the 20 years that have passed since then. The studies described herein were conducted in order to clarify the distinctness of the two species. Based on the original morphological separation, we examined whether any ecological difference could be found between the two species, and if these corresponded with their separation. Material and methods 173 specimens of G. baloni and 172 specimens of G. cernuus collected between 1989 and 1993 formed the basis of our investigations. In both cases, studied individuals originated from two different regions of the Hungarian Danube section, i.e. the Ásvány branch system in the Szigetköz area (1823-1820 rkm) and the main arm at Budapest-Háros (1635-1634 rkm), respectively. Samples were taken from possibly all existing water velocities and habitats. For collecting, we used an electric fishing machine, lift-nets and the hook-on-line method. In sampling with hook-on-line, fly larvae and Oligochaeta served as bait. Specimens collected were fixed in 10% formalin at the site of collection, and were subsequently transformed to a 40% solution of isopropyl alcohol for definite