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Reciprocal predation between non-native crayfish and salmonids Who eats whom?
MÜLLEROVÁ, Lucie
Signal crayfish (Pacifastacus leniusculus) is important invasive species in European freshwaters. Its influence on other freshwater organisms is well known from the literature, as well as direct and indirect impact on fish assemblages. This work was focused on the experimental evaluation of non-indigenous signal crayfish as a predator of salmonids compared to indigenous noble crayfish (Astacus astacus). Moreover, the possible importance of young-of-the-year signal crayfish as a prey for salmonids was assessed. There were carried out experiments using eggs and hatchings of grayling (Thymallus thymallus) as a prey for adult and subadult specimens of both, signal and noble crayfish. Next experiment used young-of-the-year signal crayfish as a prey for young-of-the-year of brown trout (Salmo trutta). Results showed that the danger of signal crayfish for grayling eggs is slightly higher. However, detected differences were surprisingly lower and in the majority of parameters even insignificant. In the case of grayling hatchings, was not detected any significant difference at all. The abilities of both tested species to prey on eggs and hatchings are therefore very similar, comparable. Even so, the effect of signal crayfish can be importantly higher in natural conditions because of its more dense populations, higher growth rate and fast maturation. In accordance to our findings, it is evident that brown trout has no so high effect of crayfish juveniles compared with crayfish effect on salmonids early developmental stages. Crayfish are therefore more likely able to limit salmonids than conversely.
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Epizoa of crayfish
PŮBALOVÁ, Lenka
The aim of my work was to evaluate quantitatively animals, which colonizes the surface of the noble crayfish (Astacus astacus). Epizoa was sampled using baths in magnesium chloride. This work was concentrate especially on the genus Branchiobdella. Data were collected from three sites. Two sites were in the Czech Republic and the third was sampling site in Austria. Two species of species occurred Branchiobdella (B. parasita and B. pentodonta) were found of the seven in Europe. Only B. parasita was found in the Czech Republic. B. parasita (88%) dominanted over B. pentodonta (12%) in Austria. Furthermore were Ciliata particularly Epistylis and Vorticella; Rotifera in the genus Keratella, Lecane and Branchionus; Acanthocyclops and Ostracoda and genus Plumatella were determined on the crayfish originated from Vodňany.
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Species variability of bentic organisms in Dračice river classicifed by PERLA system
KOUTNIK, Dalibor
Examination ecological size selected part of river (from village Františkov to border with Austria) on the basis of field watching. Observed results are analysed by system PERLA. Method is based on analysing biodiversity makrozoobenthos sample from fordables running water. Sampling can be apply in running water, where water column not exceed 1 m and speed of water stream to 1 m/s. Taking is made by normal or low water stage.
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