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)

storage. We investigated the differences in morphology, habitat use, food composition and growth. Observations made in the field are also added. 4 counts and 36 morphometric measurements (percent ratios of body length, head length and All-length) were selected as a basis for the morphological studies (for measuring points see Berinkey 1966). M, m (SE) and s (SD) were calculated for all parameters. The differences were expressed in coefficient of difference (CD) (Mayr 1969) and Student's t-test. The comparison of habitats was made on the basis of studies of bottom substrate quality, and the presence or absence of hiding places performed at the collecting site of each specimen recovered. The measurements of flow velocity were taken with modified Zhestovskiy type (GR-21M) measuring instrument primarily at Háros, as measuring the velocity of water oozing through the rock-fills in the Szigetköz area proved impossible, and the water was immobile during the period October 1992 - July 1993. Resulting parameters were given at each species as a frequency of occurrence, and were evaluated with a x~-test. Food composition was determined by investigating stomach contents. The basis of our research was formed by 75 specimens of C. baloni (46.2-127.7 mm standard length) and 86 specimens of G. cernuus (61.0-137.5 mm of standard length), collected in 1993. Food composition was given as a percental value of the number of individual prey groups. Diversity of food was expressed by Shannon-Wiener index (D). By comparison, similarity index - modified Sorensen-index (CN) (see Southwood 1984) and %

2-test were used. Growth of fish (133 specimens of G. baloni and 95 specimens of G. cernuus) was back-counted on the basis of their age determined from scale ring composition. For describing it, we used Bertalanffy's growth model. Body length/body mass relations were also expressed (see Ricker 1975, Bagenal 1978). Student's t-test was performed to compare the results. Results Morphology The results of our morphological comparisons conducted on G. baloni and G. cernuus are shown in Tables 1 and 2. Characters for separating the two forms given by other authors were useful on various levels of our investigations. In the following, we will attempt to compare these and our studies. 1. Body pattern consists of: * irregularly arranged dark dots on the body = G. cernuus * 4 to 6 dark vertical bands on the side of the body = G. baloni (after Holcik & Hensel 1974, Botta et al. 1984, Sivkov 1985, Pintér 1989). According to our observations, it can be different in some occasions. For instance, in the breeding season some G. baloni males lose their colours, and their bands disappear, whereas it remains conspicuous in females. The same can be seen during occasional high water levels in both sexes. 2. The angle between the soft portion of the dorsal fin and the lateral line on the caudal peduncle is: * perpendicular = G. baloni * acute = G. cernuus (after Holcik & Hensel 1974, Botta et al. 1984, Sivkov 1985, Pintér 1989). This characteristic is useful when separating specimens with undamaged pattern, whereas it is often invisible in damaged individuals.