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mothers clearly come from the autumnal population, the neonates born immediately after the isolation of the mothers (here referred to as 1 st offspring) had passed their oogenesis and embryogenesis at low temperatures in the reservoir, the 2 nd offspring passed their oogenesis in the reservoir and their embryogenesis in the experiment, the 3 rd offspring passed both of these ontogenetic phases in the experiment. The results reveal that low temperature was the main factor causing low FSN in neonates. 5 ºC 20 ºC FSN 70 60 50 70 60 50 lake water with natural seston GF/C filtered lake water - high food GF/C filtered lake water - low food 40 mothers 1st offspring 2nd offspring 3rd offspring 40 mothers 1st offspring 2nd offspring 3rd offspring Fig. 6: Filtering setae number (FSN) of D. galeata mothers and that of their offspring in three consecutive clutches. The mothers were isolated from Římov Reservoir on January 29 and kept in the laboratory at two temperatures and three feeding treatments (amount of the natural seston – 0.2 mg l –1 POC, high food and low food treatments – 2 and 0.2 mg l –1 POC of Scenedesmus subspicatus culture, respectively). The succession of ontogenetic phases and different temperature treatments during the experiment suggested that the time in which low temperature may induce lower FSN is very probably the period of embryonic development (embryogenesis). This was tested in another experiment, in which eggs obtained from a laboratory clone of D. galeata were incubated in vitro at three different levels of temperature. The eggs were removed several hours after being deposited in the brood pouch of the female and divided into three groups. Each group of the Table 6: Results of in vitro embryogenesis in D. galeata eggs incubated at three different temperatures (figures with different superscripts are significantly different, unequal n HSD tests, p=0.05). Temperature during embryogenesis 19°C 10°C 6°C Carapace length in the1st instar offspring (µm ± 95% C.I.) 502 (±7) a 454 (±11) b 446 (±14) b FSN in offspring (± 95% C.I.) 72 (±1) a 69 (±1) a 65 (±1) b same clutch was then incubated at a different temperature (19, 10, and 6°C). FSN was found to be significantly lower in individuals incubated during embryogenesis at the lower temperatures (Table 6). The difference in FSN is partly attributable to a difference in the body size of the neonates because the neonates from the lower temperatures were significantly smaller and a direct relationship between neonate size and FSN in their filtering screens was 32
found. The results from the field, however, indicate that this relationship itself does not explain satisfactorily the variation in FSN. [1] Pop, M., 1991: Mechanisms of the filtering area adaptation in Daphnia. Hydrobiologia 225: 169–176. [2] Repka, S., Veen, A., Vijverberg, J., 1999: Morphological adaptations in filtering screens of Daphnia galeata to food quantity and food quality. J. Plankton Res. 21: 971–989. 5.2 Sinusoidal swimming: a searching checkmate of fishes to the transparent zooplankton M. Čech (carcharhinusleucas@yahoo.com), O. Jarolím, J. Kubečka, M. Vašek, J. Peterka and J. Matěna finished their extensive, 13 years research on sinusoidal swimming in fishes. The sinusoidal swimming (Fig. 7), previously interpreted as fish foraging behaviour [1], was Fig. 7: A scheme of sinusoidal swimming (one sinusoidal cycle) of reservoir open water fish, in this case adult common bream Abramis brama, showing tilting of fish body during the ascending and descending phase of sinusoidal cycle to reach an optimal attack angle when even transparent prey (zooplankton) is clearly visible to the predator (fish). (a) Zooplankton is visible against darker depths (brighter due to light scattered in their tissue). (b) Zooplankton is practically invisible to fish horizontally scanning eyes. (c) Zooplankton is visible against the bright light of the sky (darker due to absorbance at opaque parts of the body). 33
Page 1 and 2: ACADEMY OF SCIENCES OF THE CZECH RE
Page 3 and 4: CONTENTS THE INSTITUTE, SCIENTIFIC
Page 5 and 6: Academy of Sciences of the Czech Re
Page 7 and 8: RNDr. Dagmar Sirová (maternity lea
Page 9 and 10: 1 INTRODUCTION 1.1 Directors’ pre
Page 11 and 12: 2008-2012 Reg. code 206/08/0015, Ec
Page 13 and 14: EQUIPPMET Income Reserve for invest
Page 15 and 16: 2 JAROSLAV HRBÁČEK (1921-2010) He
Page 17 and 18: 3 RESERVOIRS 3.1 Regular monitoring
Page 19 and 20: 3.3 Regular monitoring: fish stock
Page 21 and 22: Fig. 1: A - Schematic drawing of wa
Page 23 and 24: in spring and summer periods, mainl
Page 25 and 26: 3.7 Deep spawning of perch Perca fl
Page 27 and 28: In late summer, a sudden flood even
Page 29 and 30: 4 LAKES 4.1 Microbial loop componen
Page 31: 5 SPECIAL INVESTIGATIONS 5.1 Effect
Page 35 and 36: pools in forest and alpine meadow s
Page 37 and 38: Fig. 10: Effect of various glucose
Page 39 and 40: 1942 Jezberová, J., Jezbera, J., B
Page 41 and 42: B: International Proceedings or Mon
Page 43 and 44: 1980 Potužák, J.*, Duras, J.*, Bo
Page 45 and 46: APPENDIX Jaroslav Hrbáček (1921-2
Page 47 and 48: Hrbáček, J., 1981: Possibilities
Page 49 and 50: Hrbáček, J., 2000: Vztah změn po
Page 51 and 52: Hrbáček, J., 1974: Vliv hnojení

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