National Repository of Grey Literature 30 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Behaviour and electric activity of the Gnathonemus petersii species
Juhaňáková, Kateřina ; Langová, Veronika (advisor) ; Frouzová, Jaroslava (referee)
Peter's elephantnose fish (Gnathonemus petersii) is a remarkable fish of the Mormyridae family. It is set apart by its bizarre appearance and, most of all, its biology. It is one of the weakly electric fish, which are characterised by emitting electric organ discharges (EOD) placed in their caudal peduncle. They recieve and analyze EOD by other electroreceptive organs differing in function and anatomy. EOD provides active and passive electrolocation to the fish as it senses electric fields of nearby objects and animals. During active electrolocation mormyrids emit and simultaneously perceive electric signals, which enables them to analyse nearby objects. They are able to recognize an object's size, shape and material. EOD, intervals between discharges and sequences of intervals are essential in communication. Combined, they are able to transmit information about sex, hierarchy, behavioral status and environment. Other important parts of social communication are vision, olfactory, mechanosensory and auditory systems. This thesis provides an overview of existing knowledge of this species, its electric activity and behaviour. The potential of Gnathonemus petersii as a model organism in neurobiological and neuroethological studies is discussed. Key words: Gnathonemus petersii, electric activity,...
Using of stable isotopes for studies of fish otoliths
Mavrogeni, Josefína ; Frouzová, Jaroslava (advisor) ; Horká, Petra (referee)
In this work, I try to approach some general concepts related to the study of stable isotopes. The processes through which isotopes go through. Stable isotopes of some elements are suitable for ecological studies. This is due to fractionation and discrimination processes that occur during their movement through ecosystems. These movements happen due to natural cycles, which the elements undergo in one of their forms. Thanks to these cycles, isotopes enter the bodies of organisms. I especifically focus on fish tissues, primarly on otoliths. To determine the usefulness of otoliths in ecological studies, it is necessary to know their appropriate use, and the appropriate use of other tissues. The aim of this work was to gather information about the possible link between stable isotope analysis and the study of otoliths. Their composition and the information that we can obtain by examining this composition, especially the isotope composition, can be helpeful in studying the course of the fish's life and the environment in which the fish has lived in.
The impact of eutrophication on fish in running waters
Jeníšová, Karolína ; Horká, Petra (advisor) ; Frouzová, Jaroslava (referee)
Eutrophication belongs among be the most serious factors threatening freshwater ecosystems. Eutrophication is a result of excessive nutrient loading which comes mostly from both the point-source and diffuse pollution and agriculture, increased sediment loading from soil erosion, but also due to a presence of various types of impoundments, which, particularly in some areas, represent a significat part of nutrient supply. Although the effect of eutrophication on freshwater fish communities has been thoroughly studied in standing waters, very little attention has been paid to running water ecosystems. Among the processes with the most pronounced impacts on fish communities are increased phytoplankton growth and loss of macrophytes, low oxygen levels or anoxia, occurrence of toxic forms of nitrit and ammonia and elevated turbidity and subsequent light reduction. Whilst the diversity of fish communities is not usually affected, changes in structure of fish communities and decreased ecological quality has been detected with the increasing level of eutrophication. The most sensitive fishes are salmonids as they have high oxygen demands and are very sensitive to a toxic forms of nitrogen. Moreover they are visual predators highly affected by the increased turbidity of water environment. Percids are mainly...
Methane emissions from temperate freshwater reservoirs
Bašta, Jan ; Frouzová, Jaroslava (advisor) ; Rulík, Martin (referee)
Methane (CH4) emissions from temperate freshwater reservoirs have only been evaluated for the last several decades. Freshwater ecosystems (including water reservoirs) release crucial quantities of this important greenhouse gas. Ebullition that releases methane into the atmosphere from bubbles originating from sediment is important source of methane. Regardless of the importance of these emissions, a very limited number of scientific research papers monitoring this flux into the atmosphere are available. Estimated values of methane emissions from freshwater temperate reservoirs vary considerably. There are many different methods for monitoring methane emissions. It seems that the freshwater reservoir stimulates methane formation in increasing scales. The size of the sum of methane emitted from freshwater reservoirs is also difficult to say.
Methane ebullition from Czech freshwater reservoirs
Novotná, Tereza ; Frouzová, Jaroslava (advisor) ; Horká, Petra (referee)
Methane is a non-toxic colourless gas created by decomposition of organic materials in anaerobic environments. Such processes take place at bottoms of rivers, dams and water reservoirs. The gas is then released to atmosphere where it contributes to the greenhouse effect. The aim of this thesis is to measure the ebullition flux of methane from selected water reservoirs Vranov and Vír (representing typical water reservoirs in the temperate area), analyze factors affecting ebullition, and compare the ebullition flux among these two reservoirs. The data were obtained via device Simrad EK60 split beam, preprocessed in software Sonar 5, and subsequently analyzed in statistical software R. While there is a great degree of variability of ebullition flux within segments of individual water reservoirs, the total ebullition flux is comparable in both water reservoirs (Vranov: 3,90 ml·m-2 ·d-1 , Vír: 4,22 ml·m-2 ·d-1 ) and not significantly different from each other (p = 0,40). When analyzing possible factors affecting ebullition; the water depth and the distance from the dam, it is necessary to take into account that these two variables are highly correlated which may hinder our ability to separate their effects. Indeed, in both Vranov and Vir the effects of these variables, while significant when studied...
Growth of Gymnocephallus cernuus, L. in freshwater reservoirs
Hubáčková, Zuzana ; Frouzová, Jaroslava (advisor) ; Jůza, Tomáš (referee)
Gymnocephallus cernuus (Linné, 1758) doesn't belong to economically important fishes, but it is very invasive and often compete with economically important fishes. Ruffe affects populations of the economically important species by competing with them for food or by eating their eggs and fry. That is the main reason why all information about its growth, establishing and development of new population, is needed. The occurance of ruffe is currently vast, but ruffe is not indigenous species in many places. It causes reduction of the biodiversity in these areas. Many scientists are motivated by this fact and they pay more attention to ruffe. Ruffe is not required/undesirable species so there is an effort to reduce them in many of its non-original areas. For these actions a lot of information about populations of ruffe is needed. To get quantitative data about entire population of fish it is necessary to know age structure of population and the range of growth - variations in particular age - categories. This work is divided into two parts. In the literary review I have concerned with various factors which influence growth of fish and ruffes' particularly. In the third chapter I am dealing with determination of fish age. The most attention is paid to determination of age by the way of otolites. In the...
The use of otoliths for growth and population dynamics studies of Percidae and Cyprinidae in Most water reservoir
Tůmová, Eliška ; Frouzová, Jaroslava (advisor) ; Pivnička, Karel (referee)
This Master thesis compares growth of Percidae and Cyprinidae in flooded mining pit Most with water reservoir Vír, which is stable, fifty years old. Fish were cought using toils by workers from Hydrobiology institute, Academy of Sciences, Czech Republic, which are exploring fish stock. Otoliths, scales, and operculas from both families, Cyrinidae and Percidae, were removed from fish for age determination and growth back-calculation in individual years. Due to surplus of nutrients and food in flooding mining pit is assumed a huge growth difference in the first two years of life. The aim of this thesis is not only to describe the difference in the expected growth of individual species, but also to estimate its causes. At the same time will be in a very contrasting conditions compared different methods of age determination. Key words: otolith, fish age, fish population, fish growth, water reservoir, flooded mining pit, growth back-calculations
Density dependent growth of brown trout Salmo trutta in oligotrophic streams
Závorka, Libor ; Slavík, Ondřej (advisor) ; Frouzová, Jaroslava (referee)
This thesis deals with the influence of population density on the growth of brown trout Salmo trutta. The research was carried out in the Šumava National Park in the river basins of two oligotrophic streams, the Vydra and the Křemelná. Data has been collected between years 2005 and 2010, every spring and autumn. Fish were caught via electrofishing and the length and weight of each individual were measured. Every individual caught was marked in a unique way. A few samples of scales were taken from some of them. The scales were fixed into laboratory slides, scanned and measured by graphic software. According to the differences between annual lamellas density, the age and the annual growth of individual's body length were estimated. Thanks to these results a negative relationship between the individuals' of age 1+ growth rate and the population density was confirmed. The importance of this thesis is mainly in comparing the influence of different spatial and time definitions of population on this relationship. The influence of the population density in spring (the initial time of the growth period) was proved to be essential for the growth rate. This fact suggests the importance of compensation growth intensity after the long period of winter for individual's general growth under conditions provided by...
The usage of fish otholits for environmental studies
Tůmová, Eliška ; Frouzová, Jaroslava (advisor) ; Slavík, Ondřej (referee)
Otoliths are small, white minerals mostly composed of calcium carbonate. They are located in inner ear of fishes and provide balance and hearing. To the biologist, the otoliths are one of the most important structure for understanding the annual age, where and in which conditions the fish was living, and even what was its diet. This paper is focused on summarizing and ordering the use of otoliths, what methods do we use and possibilities of applications in environmental studies. Key words: otolith, fish age, fish population, chemistry otoliths, microstructure of otoliths, chemistry otoliths, fish growth

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