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Potravní zdroje plůdku reofilních ryb v rybnících s instalovanými světelnými a barevnými atraktanty hmyzu
KAJGROVÁ, Lenka
The aim of this work was to evaluate the food base (zooplankton, zoobenthos and aerial insects) and production results in culture of two-year-old golden ide (Leuciscus idus aber. orfus) and chub (Squalius cephalus). The specifics of the study were to use the attractants (yellow plates) and submersed lights as a supplement to the nutrition of farmed fish. Experimental rearing took place in the earth ponds in the area of Experimental Fish Culture Facility in Vodňany (Czechia) and in the storage ponds in Schlossfischerei Schönau bei Litschau (Austria). Zooplankton composition and physico-chemical parameters were monitored during regular two-week sampling periods. Monitoring of zoobenthos and terrestrial insects captured by attractants was performed at monthly intervals. Macrozoobenthos was sampled by Ekman Grab. After processing the samples in the laboratory, the benthic invertebrates were divided into three groups - Chironomidae, Oligochaeta and Varia. Zooplankton was collected by planktonic mesh in the 3 m long hauling and divided into the fraction of small zooplankton (Daphnidae < 499 micrometre, Copepoda < 999 and > 1000 micrometre and Others - small Cladocera), and into the fraction of coarse zooplankton (Daphnidae 500 - 999, Daphnidae 1000 - 1499 and > 1500 micrometre). Terrestrial insects were captured by installed attractants for a specified time period of day (colour attractants) or night (light attractants). The results show that the environmental conditions of the monitored ponds did not differ significantly. Abundance of coarse zooplankton in both experimental cultures was influenced by fish. The density of zoobenthos did not differ significantly. However, the values in the ponds with the lights were higher than in the control. According to the analysis of growth and production data, the installation of insect attractants as a supplementary measure to fish nutrition in aquaculture seems to be beneficial for production results. The average weight of golden ide increased during the growing season from the initial 4,3 g to 26,9 +- 4,9; 32,3 +- 6,5 and 41,2 +- 9,2 g in control ponds, ponds using lights and yellow plates, respectively. The differences between both control and experimental treatments as well as between lights and yellow plates were highly significant (p < 0,001). In the culture of chub using light attractants, the average fish weight increased from the initial 12,7 g to 41,9 +- 2,2 g, respectively to 26,7 +- 5,5 g in control. In both treatments, the production was analogously higher.
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