The construction of the Římov Reservoir on the Malše River in 1978 significantly influenced the f... more The construction of the Římov Reservoir on the Malše River in 1978 significantly influenced the fish assemblage within the river, above the reservoir. Fish species that had successfully colonised the reservoir after impoundment expanded to the inflowing river. The changes in the riverine fish assemblage up to the first impassable weir (4 km upstream) reflected the development of the reservoir assemblage after an impoundment boom of pike (<i>Esox lucius</i>), then the perch (<i>Perca fluviatilis</i>) dominated phase and later the final cyprinid-dominated phase. The changes in the fish fauna over the period 1978–2002 were significant (χ<sup>2</sup>, <i>P</i> < 0.001). During the cyprinid-dominated phase, roach (<i>Rutilus rutilus</i>) became the most abundant species both in the reservoir and in the river, outnumbering the pristine river species. We conclude that the cyprinid-dominated assemblage in the reservoir can b...
Ecological quality assessment of non-natural water bodies is, in contrast to natural systems, les... more Ecological quality assessment of non-natural water bodies is, in contrast to natural systems, less developed and requires determining biological indicators that reliably reflect environmental conditions and anthropogenic pressures. This study was motivated to propose fish indicators appropriate for assessment of reservoir ecosystems in central Europe. We analysed changes in water quality, total biomass and the taxonomic, trophic and size composition of fish communities along the longitudinal axes of four elongated, deep-valley reservoirs. Due to high nutrient inputs from their catchments, the reservoirs exhibited pronounced within-system gradients in primary productivity and water transparency. Although fish communities were similar among the reservoirs and dominated by few native species, the community structure and biomass systematically changed along the longitudinal axes of the reservoirs. The biomass and proportion of planktivores/benthivores in the fish community were highest at eutrophic sites near the river inflow and declined substantially towards deep, more oligotrophic sites close to the dam. The biomass and proportion of piscivores significantly increased downstream within the reservoirs alongside improving water quality. At species level, perch Perca fluviatilis and bream Abramis brama responded most sensitively, although in opposite directions, to the longitudinal environmental gradient. The major longitudinal changes in fish community characteristics were found to be consistent between pelagic and benthic habitats. The results of this study suggest that fish communities are appropriate indicators of eutrophication and can be used for ecological quality assessment of non-natural lentic waterbodies, such as reservoirs. Moreover, our results underline the necessity to consider within-system gradients in water quality and the fish community when planning sampling programmes for deep-valley reservoirs.
ABSTRACT We studied growth characteristics of three different spatial groups (epipelagic, bathype... more ABSTRACT We studied growth characteristics of three different spatial groups (epipelagic, bathypelagic, and littoral) of European perch (Perca fluviatilis) fry occurring simultaneously in Rímov Reservoir, Czech Republic. We used the body size analysis as long-term growth indicator and RNA/DNA ratio as short-term growth indicators. The minimum body size as well as minimum RNA/DNA ratio, was found in bathypelagic perch fry (15.7 +-1.8 and 1.89 +-0.63 mm, respectively). The littoral perch fry was the biggest with the highest RNA/DNA ratio (19.3 +-1.5 and 2.53 +-0.59 mm, respectively). The intermediate values and high variation in both body size and RNA/DNA ratio was found in the epipelagic group (16.9 +-2.3 and 2.36 +-0.78 mm, respectively). These results refer to the presence of uniformity in the bathypelagic and littoral groups, and a possible mixing of individuals from different groups in epipelagic zone. Our findings suggest that the spatial distribution of perch fry is most likely dynamic system of continuous shifting of individuals among different groups.
In July 2008, early juvenile tubenose goby Proterorhinus semilunaris were found in nocturnal pela... more In July 2008, early juvenile tubenose goby Proterorhinus semilunaris were found in nocturnal pelagic waters of the Vranov Reservoir, Czech Republic. Presence of benthic-living prey in the guts of these fish suggested migration between benthic and pelagic habitats.
ABSTRACT The DIDSON multi-beam sonar has become a popular tool for monitoring fish. The aim of th... more ABSTRACT The DIDSON multi-beam sonar has become a popular tool for monitoring fish. The aim of this study was to determine how well the DIDSON sonar can detect and measure fish during stationary applications in lakes. Cyprinid fish of known sizes (10–60 cm long) and with horizontal body orientations were deployed in known positions at two ranges (6.3 and 9.5 m) within a DIDSON high-frequency array of beams. A new method for estimating fish length from multi-beam sonars was thus developed and applied. At both ranges, all the deployed fish were invariably detected when they were aligned with their sides perpendicular to the beam. Increasing fish body angle, however, reduced the ability of the system to detect fish. Only the largest fish were detectable when the fish were parallel to the beam (head or tail aspect). The estimated fish length agreed well with the actual length when the fish were positioned perpendicular to the center of the multi-beam array. The lengths were underestimated for fish that were at the edges of the array, further away from the transducer or that had an increased body aspect, especially small-sized fish. Additionally, we observed that the wide girth of large fish can shadow the rest of the body, resulting in a decreased estimated length. We showed that determining the actual length of fish is challenging and is not a trivial task, and we raise the question of where to define fish length along the echo intensity of fish. We conclude that including the error functions for length estimates allows the DIDSON to obtain more reliable and accurate biological information.
The orientation of fish in a horizontal plane has important consequences for estimating their tru... more The orientation of fish in a horizontal plane has important consequences for estimating their true size from horizontal acoustic records. The aim of this work was to verify the assumption that during the daytime fish are randomly orientated in the lacustrine zone of the canyon-...
INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary res... more INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary research program undertaken over the period 1998–2001. Three reservoirs in Sri Lanka (Victoria, Minneriya and Udawalawe) of different morphology, age and geographic location, Ubolratana reservoir, in Thailand, and Lake Taal, in the Philippines, are the object of this study. The scope of the project encompasses a comparison of the limnology, fisheries and socioeconomic aspects of local communities in order to determine whether the trophic characteristics and key ecosystem processes sustain the available fisheries, and to examine the ecological potential for increased fish production by intensive cage culture. The paper first presents integrated results on trophic state, trophic structure and food web relationships of different water bodies. The results demonstrate the importance of ecosystem-orientated analysis in order to optimise management strategies. The broad spectrum of Asian water bodies studied allows testing of a set of hypotheses on: 1) the control of the trophic state of lakes and reservoirs by geographic, climatic and morphometric conditions; 2) the significance of the structure of the fish assemblages (bio-geography, exotic species) on ecosystem processes; 3) bottom up versus top down control under Asian reservoir and lake conditions (in comparison to established concepts for water bodies in the temperate zone); and 4) the human impact and resilience of ecosystem processes and trophic conditions towards human impact.
The construction of the Římov Reservoir on the Malše River in 1978 significantly influenced the f... more The construction of the Římov Reservoir on the Malše River in 1978 significantly influenced the fish assemblage within the river, above the reservoir. Fish species that had successfully colonised the reservoir after impoundment expanded to the inflowing river. The changes in the riverine fish assemblage up to the first impassable weir (4 km upstream) reflected the development of the reservoir assemblage after an impoundment boom of pike (<i>Esox lucius</i>), then the perch (<i>Perca fluviatilis</i>) dominated phase and later the final cyprinid-dominated phase. The changes in the fish fauna over the period 1978–2002 were significant (χ<sup>2</sup>, <i>P</i> < 0.001). During the cyprinid-dominated phase, roach (<i>Rutilus rutilus</i>) became the most abundant species both in the reservoir and in the river, outnumbering the pristine river species. We conclude that the cyprinid-dominated assemblage in the reservoir can b...
Ecological quality assessment of non-natural water bodies is, in contrast to natural systems, les... more Ecological quality assessment of non-natural water bodies is, in contrast to natural systems, less developed and requires determining biological indicators that reliably reflect environmental conditions and anthropogenic pressures. This study was motivated to propose fish indicators appropriate for assessment of reservoir ecosystems in central Europe. We analysed changes in water quality, total biomass and the taxonomic, trophic and size composition of fish communities along the longitudinal axes of four elongated, deep-valley reservoirs. Due to high nutrient inputs from their catchments, the reservoirs exhibited pronounced within-system gradients in primary productivity and water transparency. Although fish communities were similar among the reservoirs and dominated by few native species, the community structure and biomass systematically changed along the longitudinal axes of the reservoirs. The biomass and proportion of planktivores/benthivores in the fish community were highest at eutrophic sites near the river inflow and declined substantially towards deep, more oligotrophic sites close to the dam. The biomass and proportion of piscivores significantly increased downstream within the reservoirs alongside improving water quality. At species level, perch Perca fluviatilis and bream Abramis brama responded most sensitively, although in opposite directions, to the longitudinal environmental gradient. The major longitudinal changes in fish community characteristics were found to be consistent between pelagic and benthic habitats. The results of this study suggest that fish communities are appropriate indicators of eutrophication and can be used for ecological quality assessment of non-natural lentic waterbodies, such as reservoirs. Moreover, our results underline the necessity to consider within-system gradients in water quality and the fish community when planning sampling programmes for deep-valley reservoirs.
ABSTRACT We studied growth characteristics of three different spatial groups (epipelagic, bathype... more ABSTRACT We studied growth characteristics of three different spatial groups (epipelagic, bathypelagic, and littoral) of European perch (Perca fluviatilis) fry occurring simultaneously in Rímov Reservoir, Czech Republic. We used the body size analysis as long-term growth indicator and RNA/DNA ratio as short-term growth indicators. The minimum body size as well as minimum RNA/DNA ratio, was found in bathypelagic perch fry (15.7 +-1.8 and 1.89 +-0.63 mm, respectively). The littoral perch fry was the biggest with the highest RNA/DNA ratio (19.3 +-1.5 and 2.53 +-0.59 mm, respectively). The intermediate values and high variation in both body size and RNA/DNA ratio was found in the epipelagic group (16.9 +-2.3 and 2.36 +-0.78 mm, respectively). These results refer to the presence of uniformity in the bathypelagic and littoral groups, and a possible mixing of individuals from different groups in epipelagic zone. Our findings suggest that the spatial distribution of perch fry is most likely dynamic system of continuous shifting of individuals among different groups.
In July 2008, early juvenile tubenose goby Proterorhinus semilunaris were found in nocturnal pela... more In July 2008, early juvenile tubenose goby Proterorhinus semilunaris were found in nocturnal pelagic waters of the Vranov Reservoir, Czech Republic. Presence of benthic-living prey in the guts of these fish suggested migration between benthic and pelagic habitats.
ABSTRACT The DIDSON multi-beam sonar has become a popular tool for monitoring fish. The aim of th... more ABSTRACT The DIDSON multi-beam sonar has become a popular tool for monitoring fish. The aim of this study was to determine how well the DIDSON sonar can detect and measure fish during stationary applications in lakes. Cyprinid fish of known sizes (10–60 cm long) and with horizontal body orientations were deployed in known positions at two ranges (6.3 and 9.5 m) within a DIDSON high-frequency array of beams. A new method for estimating fish length from multi-beam sonars was thus developed and applied. At both ranges, all the deployed fish were invariably detected when they were aligned with their sides perpendicular to the beam. Increasing fish body angle, however, reduced the ability of the system to detect fish. Only the largest fish were detectable when the fish were parallel to the beam (head or tail aspect). The estimated fish length agreed well with the actual length when the fish were positioned perpendicular to the center of the multi-beam array. The lengths were underestimated for fish that were at the edges of the array, further away from the transducer or that had an increased body aspect, especially small-sized fish. Additionally, we observed that the wide girth of large fish can shadow the rest of the body, resulting in a decreased estimated length. We showed that determining the actual length of fish is challenging and is not a trivial task, and we raise the question of where to define fish length along the echo intensity of fish. We conclude that including the error functions for length estimates allows the DIDSON to obtain more reliable and accurate biological information.
The orientation of fish in a horizontal plane has important consequences for estimating their tru... more The orientation of fish in a horizontal plane has important consequences for estimating their true size from horizontal acoustic records. The aim of this work was to verify the assumption that during the daytime fish are randomly orientated in the lacustrine zone of the canyon-...
INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary res... more INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary research program undertaken over the period 1998–2001. Three reservoirs in Sri Lanka (Victoria, Minneriya and Udawalawe) of different morphology, age and geographic location, Ubolratana reservoir, in Thailand, and Lake Taal, in the Philippines, are the object of this study. The scope of the project encompasses a comparison of the limnology, fisheries and socioeconomic aspects of local communities in order to determine whether the trophic characteristics and key ecosystem processes sustain the available fisheries, and to examine the ecological potential for increased fish production by intensive cage culture. The paper first presents integrated results on trophic state, trophic structure and food web relationships of different water bodies. The results demonstrate the importance of ecosystem-orientated analysis in order to optimise management strategies. The broad spectrum of Asian water bodies studied allows testing of a set of hypotheses on: 1) the control of the trophic state of lakes and reservoirs by geographic, climatic and morphometric conditions; 2) the significance of the structure of the fish assemblages (bio-geography, exotic species) on ecosystem processes; 3) bottom up versus top down control under Asian reservoir and lake conditions (in comparison to established concepts for water bodies in the temperate zone); and 4) the human impact and resilience of ecosystem processes and trophic conditions towards human impact.
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Papers by J. FrouzovÁ