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Biology of predatory fishes in dam reservoirs and lakes
VEJŘÍK, Lukáš
This Ph.D. Thesis is focused mainly on the biology of two typical European predatory fishes, European catfish (Silurus glanis) and perch (Perca fluviatilis). Catfish is a typical apex predator, whereas perch is a smaller species that plays role of a mesopredator. Although, catfish is the third largest freshwater fish in the world, only few studies dealing with this species have been revealed thus far. The main reason is connected with capturing of the species that is inefficient by standard ichthyologic methods. Studies, that have been revealed recently, focused mainly on expansions of catfish to the West and South Europe. Catfish is unwanted in these localities due to a potential negative impact on native fish community, thus its reduction is desirable. In contrast, catfish occurrence is important in native localities where it plays a key role as a biomanipulative species (I). Catfish is a true generalist, which is a typical feature for large-bodied apex predators connected with high energy consumption of their bodies. The second typical feature is a wide diet plasticity and thus good adaptability to new food sources. It is associated with distribution of various food sources among individuals within the population (II). By contrast, perch is one of the most studied fish in the world and hundreds of studies with IF are revealed every year. However, the more information about biology of perch have been known, the more questions have been arisen. Several phenomena are revealed also in this thesis. For instance, crucial impact of juvenile perch on the entire ecosystem is described. High predation pressure on zooplankton may induce piscivory in primarily zooplanktivorous fish (III). Further, juvenile perch utilize hypoxic pelagic zones as a refuge against predation (IV). The last surprising phenomenon is described in the study dealing with both species, catfish and perch. Their coexistence may lead in strong discrimination of one species caused by special predation that was supposed to be implausible (V).
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Crayfishes as a prey
MAN, Milan
Due to the increase in the number of non-native species of crayfishes and their presence on more and more localities, there is the possibility of their elimination using predatory fish species. The length relationships between a prey and a predator could clarify this possibility. The aim of this bachelor thesis was to develop high quality literary review about the incorporation of crayfish into the food chain and processing samples of a perch (Perca fluviatilis) from a locality with an occurrence of juvenile crayfishes (Astacus astacus). I wanted to verify the possibility of a perch predation on juvenile crayfish individuals. However, only three crayfishes were found in the analyzed perchs. After a very low percentage of crayfishes in the analyzed perchs, a laboratory experiment was carried out with young of the year of signal crayfish (Pacifastacus leniusculus) and perchs. Unfortunately, this experiment ended unexpectedly. The crayfishes were served to perchs, but the fishes showed no interest in them throughout the experiment. The results of food analysis show, that smaller perchs are able to eat crayfish, but they are not a sought-after component of their diet. In this case, the low frequency of crayfishes in the diet was caused by enough other food (insect larvae) and also the number of shelters in the pond, where the crayfishes were reared. In the experiment, I unfortunately failed to confirm the positive relationship between a perch as a predator and a juvenile crayfish as a prey. However, the conclusions of the other studies on the use of larger perchs show the preference and high frequency of occurence of juvenile crayfishes in their diet.
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Fish stock assessment of the Petrusplaat Reservoir in 2015, Fish stock assessment of the Honderd en Dertig Reservoir in 2015.
Jůza, Tomáš ; Soukalová, Kateřina ; Kočvara, Luboš ; Prachař, Zdeněk
The report (1) summarizes the results of the complex ichthyological survey of the Petrusplaat Reservoir in 2015. Species composition, abundances, biomasses and age composition of fish were investigated based on gillnets, seine nets, trap nets and trawl catches. Obtained results were also compared with data from previous surveys. The report (2) summarizes the results of the complex ichthyological survey of the Honderd en Dertig Reservoir in 2015. Species composition, abundances, biomasses and age composition of fish were investigated based on gillnets, seine nets, trap nets and trawl catches. Obtained results were also compared with data from previous surveys.
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Demembranation of fish sperm: Design and verification this procedure for the different species of freshwaterfish and demonstration usage of this technique by study the effect of heavy metals to sperm axoneme
BLAŽKOVÁ, Jaroslava
The object of this study is to design demembranation method on four freshwater species and its application on study of the influence of HgCl2 on the axoneme and motity sperm motility parameters. Demembranation was designed and examined for all investigated species common carp (Cyprinus carpio), sterlet (Acipenser ruthenus), perch (Perca fluviatilis) and african catfish (Clarias gariepinus). One-step and two-step method was designed and tested for common carp. One-step method was designed for sterlet and perch. Two-step method of demembranation was designed for african catfish. Demembranation was designed and examined for all species under examination. Sperm motility was evidently increased above normal physiological value. Other sperm motility parameters (velocity, percent of motile cells) slightly decreased. HgCl2 in concentration 0,01 mM to the demembranation medium didn't show effect on flagellar microtubule aparat and then to the motility parameters, except sterlet; demembranated sterlet sperm was inhibited at all used concentration of HgCl2. Concentration 0,1 mM had inhibition effect on carp and africant catfish spermatozoa. Concentration 1 mM HgCl2 inhibited sperm of all tested species.
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Different effects of planktonic invertebrate predators and fish on the plankton community in experimental mesocosms
ŠORF, Michal
The impact of fish and cyclopoid copepod predation on zooplankton communities was evaluated using large-volume mesocosms (depth 9.5 m; volume 13 m3) in the Římov reservoir (Czech Republic). Two yearling roach and perch individuals introduced into mesocosms represented the fish treatment, which was compared to cyclopoid copepods (initial abundance of 2 ind.L-1) and a control with no initial addition of predators. Our results clearly support the hypothesis that planktivorous fish feeding leads to the suppression of large-bodied cladocerans. In the presence of fish, the cladoceran community changed from a dominance of large-bodied Daphnia spp. at the beginning to dominance by the smaller Bosmina longirostris at the end of the experiment. The overall strong effect of fish over cyclopoid predation suggests the main role of fish predation in the forming of zooplankton communities and in turn impacting phytoplankton biomass in mesocosms.
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Comparision of rate of pike and pike perch cannibalism in first year of life
SVATEK, Petr
Abstract Larvae of perch (100-200 thousand per ha) were planted into the ponds Bejkovna (1,33 ha) and Kamenný (1,54 ha). Larvea of pikeperch (150 - 300 thousand per ha) into the ponds Hejškův (0,88 ha) and Hadač (2,7 ha). Pond Bagr was used such as an additional data source. The aim of this study was Comparision of rate of pike and pike perch cannibalism in first year of life. There wasn?t observed cannibalism and different sizes of perch individuals in the ponds Bejkovna and Kamenný. Total length (TL) of the fish was 50,5 ? 2,85 mm in the pond Bejkovna and 41,58 ? 1,56 mm in the pond Kamenný at the end of observed period. Average growth rate was 0,86 mm/day in pond Bejkovna and 0,7 mm/day Kamenný. There was also no cannibalism by the perch (TL = 57,2 ? 1,34 mm) from the pond Bagr. It was possible to observe few individuals of roach (Rutilus rutilus) in the digestive tract. The level of cannibalism was 23 % in the pond Hadač and also in the pond Hejškův. The average TL was 31,59 ? 3,89 mm (average growth rate 0,9 mm/day) in the pond Hadač at the beginning of June and 26,83 ? 2,51 mm (average growth rate 0,77 mm/day) in the pond Hejškův. The average TL was 48,7 ? 10,04 mm in the pond Hadač at the end of June. There was observed cannibalism in the pond Hadač at the beginning of the June and also at the end of this month. TL of prey fish was 66,1 and 61,6 % of cannibals TL. There was observed cannibalism in the pond Hejškův until the mid of September. The average TL was 140,6 ? 35,4 mm here and cannibalism was observed in 23 % of cases. TL of prey fish was 54,9 % cannibals TL. The most important thing of the monoculture rearing of perch and pikeperch is sufficient amount of food. This is especially true in the case of pikeperch. Key words: Cannibalism, pike perch, perch
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Food of predatory fish during the flooding of the Chabařovice coal mining pit
KABILKA, Petr
The Chabařovice coal mining pit is currently still under the process of continuous flooding and its area increased up to 174 ha since 2001.Adult perch (Perca fluviatilis) have been the most numerous fish of the lake until 2004. Fish were collected during the ichtyological survey sampling campaigns in June and September.Diet composition was expressed as percent weight, which was calculated for each prey taxon.
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Potrava okouna říčního (Perca fluviatilis) v průběhu napouštění důlní propadliny Chabařovice (SZ Čechy, ČR)
Adámek, Zdeněk ; Jurajda, Pavel ; Musil, J. ; Janáč, Michal ; Kabilka, P. ; Polačik, Matej ; Ťuk, J. ; Valová, Zdenka ; Zeman, J.
The Chabařovice coal mining pit (Chabařovice lake) is currently still under the process of continuous flooding and its area increased up to 174 ha since 2001. The inflow water originates from surface waterbodies and hence the penetration of fish species, undesirable with respect to biomanipulation efforts, makes a serious problem in fisheries management of the lake. Adult perch have been the most numerous fish of the lake until 2004. Current perch population consists of one cohort (7+ - 8+) originating from the recruitment of two subsequent year classes. The food bulk of adult perch consisted of benthic animals and zooplankton in both years under study, however their proportion differed significantly. In 2004, dragon fly nymphs were the dominant food items with 58.80% proportion, followed by cladocerans Daphnia sp., which made up 23.82% of food ingested. In 2005, chironomid larvae prevailed in the food bulk with 41.95% and the diversity of ingested food items was obviously wider.
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