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Vliv přítomnosti či absence střevličky východní (Pseudorasbora parva) na produkci ryb a kvalitu vody v rybnících firmy Blatenská ryba
KOUKOLÍK, Pavel
Topmouth gudgeon (further TG) Pseudorasbora parva (Temminck & Schlegel, 1846) is a small cyprinid naturally occurring in East Asia. TG causes a lot of economic lossess on the pond culture worldwide including Czech Republic. The aim of the present B.Sc. thesis was to assess an effect of TG on fish production and water quality in the ponds of the Blatenská ryba company. The experiment was perfomed in six ponds. Three of them had a control function where two-years common carp was stocked and necessary preventive measures were taken to rule out presence of any pest species. The other three ponds were also stocked by carp, but TG was stocked as well. Water, zooplankton, zoobenthos samples collecting, water properties measurements, topmouth gudgeon sampling and morphometric-gravimetric analyses of caught carp were performed on monthly basis from March to September. From the end of September to the the first half of October all six ponds were harvested, when the overal final fish biomass, health and physical (TL, SL, W, Fulton) condition of the cultured carp were monitored. A remarkable negative influence of TG upon water quality and pond production parameters were found. The impact of TG on water quality is believed to be indirect, due to mass elimination of big size zooplankton species (Daphnia sp.). Zooplankton unavailability caused the carp's foraging shift to zoobenthos, and afterwards carp bioturbation activity when carp digged in the pond ground. This activity resulted in intensive phosphorus releasing from the sediment to the water collumn which in combination with zooplankton absence led to water quality worsening. Moreover, TG presence also had a negative impact on pond production parameters and the health status of the carp stock. Production in ponds with TG was on average 70 % lower compared to the control group. In addition, 29 % of carp suffered from tissue lesions as a consequence of facultative parasitism of TG. The conclusions of the thesis clearly proved that it is necessary to take effective measures to control TG occurrence in pond aquaculture to ensure better economic results and stability of the pond environment.
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