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)
Table 3. The growth of Gymnocepfuilus baloni and G. cernuus in the Danube - back counted data. Gymnocephalus cernuus Him Szigetköz age body length weight growth body length weight growth (years) (mm) + s (g) + 3 (mm) (mm) * s (g) • 5 (mm) 0+ 32.7 + 3.0 0 7 + 03 32.7 36.0 J 3.0 0.8 + 0.2 36.0 1 + 49.4 * 50 2.6 ± 0.7 16.7 55.7 * 5.6 34 • 11 19.7 2+ 65.5 + 6.0 6.2 + 1.8 16.1 73.0 ± 5.8 7.8 ± 1.9 17.3 3+ 80 7 + 6 8 11.2 + 3,1 15.2 90.1 ± 6.9 14.8 i 3.7 17.1 4+ 95.5 + 7.2 19.9 + 4 7 14.8 106.3 • 4 1 23.5 ± 4.4 16.2 5+ 105.7 * 7.8 27.3 + 6.3 10.2 118.7 t 5 5 30.2 12.4 6+ 114.8 ï 5.1 35.3 + 5.1 9.1 121.7 40.1 3.0 7+ 122.0 + 36 42.6 î 4.4 72 8+ 129.2 51.0 7.2 9+ 137.5 61.0 83 Gymnocephalus baloni Hiros Szigetköz age body length weight growth body length weight growth (years) (mm) + s (a) t s (mm) Jmm) + 3 (fl) • 3 (mm) 0+ 32 2 • 3 1 0.6 + 0.2 32.2 31.2 * 26 0.7 + 02 31.2 1+ 49.8 + 4.5 2.5 • 0.5 17.6 49.4 + 4 4 2.7 + 0 8 18.2 2+ 67.7 J 6.2 7.3 ± 2.3 17.9 66.7 i 5.8 7.0 + 2.0 17.3 3+ 84.5 + 6.3 15.8 + 4.1 16.8 82.2 • 65 1Z7 i 27 15.5 4+ 97.5 1 5.6 25 9 • 52 13 95.9 + 6.4 22.1 • 3.0 13.7 5+ 111.9 ± 7.7 41.9 ± 10.0 14.4 108.8 + 6.9 25.5 12.9 6+ 119.3 i 5.2 5Z3 ± 8.0 7.4 120.1 ± 6.4 11.3 7+ 127.7 655 84 132 5 12.4 decreases afterwards. In the seventh to eighth year of age only 3-8 mm annual growth could be observed. When comparing the two populations of G. cernuus one can conclude that conditions for growth were more favourable in the Szigetköz branch system than at Háros (t-test values p<0.001 for ages 0 + to 4 + , whereas p<0.05 for age group 5 + ). Our measurements are to be found in Table 3, and in Figs 3, 4. Growth of G. cernuus at Háros can be described by Bertalanffy's curve Lt (cm) = 19.4 n -0.121 (t + 0.503X J • .î o • *i •• u T t \ «1 /1 -0.095 (t + 0.567k (1-e ), and in the Szigetköz by Lt (cm) = 25.7 (1-e 1 '). Body length/body mass relations were determined on the basis of samples collected in 1993: lgw = 3.11 IgL - 4.86 (R 2 = 0.98, n = 51) (Háros) lgw =3.13 IgL - 4.96 (R 2 = 0.98, n = 37) (Szigetköz). Growth of males and females was statistically similar, except for age group 5 + at Háros, in which males proved to be larger (p<0.05). Feeding Gymnocephalus baloni The food of G baloni was already investigated by Nagy (1985, 1986) in the Csallóköz section of the Danube. The results of our examinations of the food composition in this species are shown in Figs 5a and 5b. The food of this species was more varied (D = 1.58) in the Háros section than in the Szigetköz area (D = 0.93). The dominant food in both areas were chironomid larvae (and pupae). Besides, the proportion of leeches (Herpobdella octoculata, Helobdella stagnalis) was significant at Háros, particularly considering their size. The role of snails, web-building
