Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ j... more Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ juveniles were monitored in the epipelagic and bathypelagic layers near the dam, and in the middle and upper sections at the canyon‐shaped Římov Reservoir (Czech Republic) during the day on 26 and 29 May, and during the night on 5 and 11 June in 2008. The greatest abundance of 0+ fish was observed in the middle section of the reservoir and their LS increased upstream from the dam towards the reservoir's tributary. Moreover, larger and older pikeperch 0+ juveniles migrated to the bathypelagic layer during the day. The epilimnetic temperature and productivity (expressed as chlorophyll‐a concentration) gradients were suggested as the main drivers affecting the distribution and growth of the fish.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
1. Generalist fishes commonly show intraspecific niche segregation along the littoral-pelagic res... more 1. Generalist fishes commonly show intraspecific niche segregation along the littoral-pelagic resource axis in lakes. Recent studies have shown that the deep, cold and seemingly unproductive profundal zone can also offer underutilised resources and facilitate specialised individuals, and can contribute to lake food webs via methane-derived carbon pathways. Despite numerous examples from salmonid fish species, such intraspecific niche segregation along a littoral-profundal resource axis has not been reported in percids or other predominantly littoral benthivorous fishes. 2. Here, we describe a case of ruffe (Gymnocephalus cernua: Percidae) populations consisting of shallow-and deep-water dwelling individuals in two post-mining lakes in the northern Czech Republic. Results from stable isotope (d 15 N and d 13 C) mixing models indicated that littoral and profundal food resources dominated the long-term diets of ruffe individuals caught from shallow-and deep-water habitats, respectively. No similar niche segregation along the littoralprofundal gradient was observed in coexisting perch (Perca fluviatilis: Percidae) which used more pelagic food than the benthivorous ruffe. 3. The observed littoral-profundal niche segregation in ruffe was more pronounced in the macrophyte-rich and poorly oxygenated Lake Milada, where high habitat complexity and strong interspecific interactions in the littoral zone as well as the absence of competing fish species in the profundal zone likely promote narrow trophic niches of shallow-and deep-water dwelling ruffe 4. Our study provides novel evidence of littoral-profundal niche segregation in a predominantly benthivorous fish species. The results also show that intraspecific niche variation can be affected by lake ecosystem characteristics, in particular by the availability of and competition for littoral and profundal resources. Although more research is needed to confirm potential early divergence of shallow-and deep-water dwelling ruffe as well as cascading effects on lake ecosystem processes (e.g. nutrient cycling and competitive and predatory interactions), our study indicates that individual ruffe may show limited habitat and food-web coupling due to their restricted use of shallow or deep resources.
Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtai... more Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtaining a representative sample of fish community composition is fundamental to fishery management, research and nature conservation. Estimates of the size distribution, density and biomass of the topmouth gudgeon (Pseudorasbora parva) model species of invasive fish in three ponds were compared among three sampling methods: electrofishing, fish‐trapping and throw‐netting. The study illustrates that the invasive fish, P. parva, can be detected by all tested fishing methods, yet our results clearly showed that there are pronounced differences among methods in population characteristic estimates. Electrofishing and throw‐netting gave biased information on the size distribution of P. parva. Fish‐trapping and throw‐netting gave reasonable P. parva density and biomass estimates, while electrofishing clearly underestimated it. All tested methods showed a body size increment of P. parva between summer and autumn sampling sessions, yet neither throw‐netting nor electrofishing recorded an increment in its density. Our study showed that fish‐trapping is the most reliable and affordable method to estimate invasive P. parva population characteristics in ponds despite more time‐demanding sampling. The success depends on the mesh size of sampling gear, operator skill and habitat structure. The cost‐effectiveness of the selected methods and the importance of invasive fish monitoring in ponds is discussed. The sampling gear must be considered carefully according to the aim of the monitoring.
Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutc... more Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutch reservoir revealed extremely small age-0 year pikeperch Sander lucioperca (mean 24 mm standard length, LS , minimum 13 mm LS ) alongside more normal-sized S. lucioperca that are found at the end of the first growing season (mean 50 mm LS ), resulting in two clearly size-separated cohorts. Reference to such small age-0 year S. lucioperca in lakes or reservoirs at this time of year and in such large numbers are almost absent the scientific literature, and the presence of these small S. lucioperca is contradictory to the common understanding of the reproductive biology of this species. This overlooked phenomenon may have a major effect on the population dynamics of this valuable species because of size-dependent winter mortality.
Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtai... more Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtaining a representative sample of fish community composition is fundamental to fishery management, research and nature conservation. Estimates of the size distribution, density and biomass of the topmouth gudgeon (Pseudorasbora parva) model species of invasive fish in three ponds were compared among three sampling methods: electrofishing, fish‐trapping and throw‐netting. The study illustrates that the invasive fish, P. parva, can be detected by all tested fishing methods, yet our results clearly showed that there are pronounced differences among methods in population characteristic estimates. Electrofishing and throw‐netting gave biased information on the size distribution of P. parva. Fish‐trapping and throw‐netting gave reasonable P. parva density and biomass estimates, while electrofishing clearly underestimated it. All tested methods showed a body size increment of P. parva between sum...
Biomonitoring of complex heterogeneous environments is highly challenging. Fish in deep water bod... more Biomonitoring of complex heterogeneous environments is highly challenging. Fish in deep water bodies occupy different habitats, therefore a combination of survey methods has traditionally been used. Environmental DNA (eDNA) metabarcoding is a novel monitoring tool that can overcome spatial heterogeneity in a highly sensitive and entirely non-invasive manner. However, taxon detection probability is dependent on real-time environmental variables. In this study, three reservoirs were sampled in two seasons using a spatiotemporally distributed sampling design covering major environmental gradients. In all sampling campaigns, 31 fish taxa were detected which exceeded expectations. Data reliability was confirmed by a tight positive correlation between individual taxon scores derived from gillnet sampling and eDNA site occupancy. Analyses confirmed anticipated trends, such as the highest number of taxa were observed in the largest water body, and more taxa were detected in inflows and littoral regions compared to open water. The most important factors for fish distribution were temperature, age and trophic status (expressed as total Chlorophyll a concentration) of water bodies. Taxon detection reflected ecological niches of individual species, e.g. warm water wels catfish (Silurus glanis) and cold water salmonids. This study provides further evidence that eDNA metabarcoding is suitable for ecological study in heterogeneous environments and may substitute conventional fish sampling techniques.
Intra-species variability in a diet niche, speci cally total niche width (TNW), individual niche ... more Intra-species variability in a diet niche, speci cally total niche width (TNW), individual niche width (INW), and individual specialization (IS), was studied using an innovative approach without sacri cing the animals. Stable isotopes (δ 13 C, δ 15 N) in four body tissues differing in isotopic half-life were analyzed from four freshwater sh species representing different trophic positions. TNW was widest for the apex predator (European cat sh) and narrowest for the obligate predator (Northern pike). INW exhibited a polynomial trend for European cat sh, Northern pike and Eurasian perch (mesopredator), decreasing with body mass and increasing again after exceeding a certain species-dependent body mass threshold. Thus, for ectotherms, apex predator status is linked rather to its size than to the species. In herbivores (rudd), INW increased with body mass. IS of predators negatively correlated with site trophic state. The trends can be generalized to other species at similar trophic positions in either aquatic or terrestrial systems.
1. Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic envi... more 1. Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environment. A general pattern of DVMs has been well described, particularly in European perch (Perca fluviatilis), but whether the migrations are directly controlled by light and what is the ultimate cause of the diel vertical shifts, remains poorly understood. 2. Undertaking a large-scale field experiment in a thermally stratified, canyon-shaped reservoir, we demonstrated for the first time that DVMs of a bathypelagic early juveniles community, dominated by European perch larvae and juveniles prior the metamorphosis, were under direct control of the light intensity; that is, they did not operate as a genetically fixed behaviour. 3. Prior to the experiment, the depth distribution of the bathypelagic perch early juveniles was strongly correlated with the light intensity on the water surface (p < .001). The community underwent regular DVMs between the epilimnion (depth <2.0 m) and hypolimnion (depth >3.0 m) reaching a maximum amplitude of 13 m. 4. Hydroacoustic recordings by the echosounder SIMRAD EK 60 (120 and 400 kHz) showed that during the experiment, when the surface was covered with a large black non-transparent foil (2500 m 2 ; simulated conditions of complete and constant darkness), the regular vertical movement of the bathypelagic perch early juveniles was interrupted and the community occupied the epilimnion constantly for 24 hr. 5. Immediately after the foil was removed at midday, the bathypelagic perch early juveniles were exposed to a steep increase in light intensity (from <1 LUX to >100 9 10 3 LUX) and they escaped into the hypolimnion where they were safe from visual predation which took place in the bright surface layers (epilimnion particularly). Our findings imply that occupying a deep, dark refuge in the daytime is essential for the survival of perch in their early life stage.
Abstract Fish recruitment in riverine reservoirs is not fully understood because the long-term da... more Abstract Fish recruitment in riverine reservoirs is not fully understood because the long-term data series required for standard stock–recruitment models are often lacking. In this study, two unrelated piscivorous species with different ecologies, asp ( Leuciscus aspius ) and pikeperch ( Sander lucioperca ), were investigated over a 14-year period in a reservoir in the Czech Republic using a novel informative statistical approach based on dimension reduction methods. This method is useful for situations in which potential predictors are equal to, or exceed, the length of the time series. Recruitment of asp fry was affected by zooplankton abundance, predator density and temperature. Recruitment of pikeperch fry measured with seine and trawls was only affected by the number of predators, while recruitment of pikeperch fry estimated with gillnet data was also affected by temperature and water level fluctuation. Although gillnets are commonly used sampling method, it seems to be inappropriate for developing fry predicting model. This research also highlights the use of a novel approach to dimension reduction for analysis of factors affecting recruitment using shorter time series (in our case 13 years).
Ligula intestinalis (Linnaeus, 1758) is a tapeworm parasite with a worldwide distribution that us... more Ligula intestinalis (Linnaeus, 1758) is a tapeworm parasite with a worldwide distribution that uses a wide variety of fish species as its second intermediate host. In the present study, we investigated the prevalence and population genetic structure of plerocercoids of L. intestinalis in five common cyprinoid species, roach Rutilus rutilus (Linnaeus), freshwater bream Abramis brama (Linnaeus), white bream Blicca bjoerkna (Linnaeus), bleak Alburnus alburnus (Linnaeus), and rudd Scardinius erythrophthalmus (Linnaeus), collected in six water bodies of the Czech Republic (Milada, Most, Medard, Jordán, Římov and Lipno). Of the six study sites, the highest frequency of parasitism was recorded in Lake Medard (15%). The overall prevalence rate among the species was as follows: roach > rudd ≥ freshwater bream > bleak > white bream. Two mitochondrial genes (cytb and COI) were used to compare the population genetic structure of parasite populations using selected samples from the five fish species. The results of the phylogenetic analysis indicated that all populations of L. intestinalis were placed in Clade A, previously identified as the most common in Europe. At a finer scale, haplotype network and PCoA analyses indicated the possible emergence of host specificity of several mtDNA haplotypes to the freshwater bream. Moreover, pairwise Fixation indices (F ST) revealed a significant genetic structure between the parasite population in freshwater bream and other host species. Parasite populations in roach not only showed the highest rate of prevalence but also depicted a maximum number of shared haplotypes with populations from bleak and rudd. Our results suggest that recent ecological differentiation might have influenced tapeworm populations at a fine evolutionary scale. Thus, the differences in prevalence between fish host species in different lakes might be influenced not only by the parasite's ecology, but also by its genetic diversity.
Structural complexity is known to influence prey behaviour, mortality and population structure, b... more Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake-LSC; high structural complexity-HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent with a prevalent ambush predation behaviour, whereas the higher activity and larger space use in the LSC lake indicated a transition to more active search behaviour. It could lead to increased prey encounter and cause better growth in the LSC lake. Our study demonstrated how differences in structural complexity mediated prominent changes in the foraging behaviour of an apex predator, which in turn may have effects on the prey community.
Fish otoliths are conservative structures that are widely used on fishery science for multiple pu... more Fish otoliths are conservative structures that are widely used on fishery science for multiple purposes. Despite its relevance in the research field, little is known about the ontogeny and inter-population effects on the otolith of freshwater fish. In this study we used otoliths from 1800 European perch (Perca fluviatilis) individuals from 9 different populations to analyze the ontogenetic and interpopulation differences on the otolith shape using six morphometric indices. The relationship between fish and otolith length was fitted using three different regression models (linear, power and logistic) to identify the best allometric relationship. Our results show that there are strong ontogenetic and interpopulation differences in P. fluviatilis otolith shapes. We also show that the relationship between the fish and otolith length follows a logistic curve. The ontogenetic differences on otolith shape might be related to extrinsic factors (diet shift and intra and interspecific competition) in each ecosystem, *Manuscript including abstract Click here to view linked References 2 given that the reservoirs are different and no clear pattern on the otolith shapes can be distinguished among populations. Our results imply that the available back-calculation models may not always provide accurate estimates of P. fluviatilis length and that a model that takes into account the real allometric relationship for the species can improve the fish length estimations of back-calculated fish lengths for the European perch.
Differential use of habitat and prey resources is an important mechanism that may allow coexisten... more Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0-65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.
Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ j... more Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ juveniles were monitored in the epipelagic and bathypelagic layers near the dam, and in the middle and upper sections at the canyon‐shaped Římov Reservoir (Czech Republic) during the day on 26 and 29 May, and during the night on 5 and 11 June in 2008. The greatest abundance of 0+ fish was observed in the middle section of the reservoir and their LS increased upstream from the dam towards the reservoir's tributary. Moreover, larger and older pikeperch 0+ juveniles migrated to the bathypelagic layer during the day. The epilimnetic temperature and productivity (expressed as chlorophyll‐a concentration) gradients were suggested as the main drivers affecting the distribution and growth of the fish.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
1. Generalist fishes commonly show intraspecific niche segregation along the littoral-pelagic res... more 1. Generalist fishes commonly show intraspecific niche segregation along the littoral-pelagic resource axis in lakes. Recent studies have shown that the deep, cold and seemingly unproductive profundal zone can also offer underutilised resources and facilitate specialised individuals, and can contribute to lake food webs via methane-derived carbon pathways. Despite numerous examples from salmonid fish species, such intraspecific niche segregation along a littoral-profundal resource axis has not been reported in percids or other predominantly littoral benthivorous fishes. 2. Here, we describe a case of ruffe (Gymnocephalus cernua: Percidae) populations consisting of shallow-and deep-water dwelling individuals in two post-mining lakes in the northern Czech Republic. Results from stable isotope (d 15 N and d 13 C) mixing models indicated that littoral and profundal food resources dominated the long-term diets of ruffe individuals caught from shallow-and deep-water habitats, respectively. No similar niche segregation along the littoralprofundal gradient was observed in coexisting perch (Perca fluviatilis: Percidae) which used more pelagic food than the benthivorous ruffe. 3. The observed littoral-profundal niche segregation in ruffe was more pronounced in the macrophyte-rich and poorly oxygenated Lake Milada, where high habitat complexity and strong interspecific interactions in the littoral zone as well as the absence of competing fish species in the profundal zone likely promote narrow trophic niches of shallow-and deep-water dwelling ruffe 4. Our study provides novel evidence of littoral-profundal niche segregation in a predominantly benthivorous fish species. The results also show that intraspecific niche variation can be affected by lake ecosystem characteristics, in particular by the availability of and competition for littoral and profundal resources. Although more research is needed to confirm potential early divergence of shallow-and deep-water dwelling ruffe as well as cascading effects on lake ecosystem processes (e.g. nutrient cycling and competitive and predatory interactions), our study indicates that individual ruffe may show limited habitat and food-web coupling due to their restricted use of shallow or deep resources.
Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtai... more Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtaining a representative sample of fish community composition is fundamental to fishery management, research and nature conservation. Estimates of the size distribution, density and biomass of the topmouth gudgeon (Pseudorasbora parva) model species of invasive fish in three ponds were compared among three sampling methods: electrofishing, fish‐trapping and throw‐netting. The study illustrates that the invasive fish, P. parva, can be detected by all tested fishing methods, yet our results clearly showed that there are pronounced differences among methods in population characteristic estimates. Electrofishing and throw‐netting gave biased information on the size distribution of P. parva. Fish‐trapping and throw‐netting gave reasonable P. parva density and biomass estimates, while electrofishing clearly underestimated it. All tested methods showed a body size increment of P. parva between summer and autumn sampling sessions, yet neither throw‐netting nor electrofishing recorded an increment in its density. Our study showed that fish‐trapping is the most reliable and affordable method to estimate invasive P. parva population characteristics in ponds despite more time‐demanding sampling. The success depends on the mesh size of sampling gear, operator skill and habitat structure. The cost‐effectiveness of the selected methods and the importance of invasive fish monitoring in ponds is discussed. The sampling gear must be considered carefully according to the aim of the monitoring.
Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutc... more Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutch reservoir revealed extremely small age-0 year pikeperch Sander lucioperca (mean 24 mm standard length, LS , minimum 13 mm LS ) alongside more normal-sized S. lucioperca that are found at the end of the first growing season (mean 50 mm LS ), resulting in two clearly size-separated cohorts. Reference to such small age-0 year S. lucioperca in lakes or reservoirs at this time of year and in such large numbers are almost absent the scientific literature, and the presence of these small S. lucioperca is contradictory to the common understanding of the reproductive biology of this species. This overlooked phenomenon may have a major effect on the population dynamics of this valuable species because of size-dependent winter mortality.
Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtai... more Invasive fish threaten ponds' ecological status and their ecosystem services, therefore obtaining a representative sample of fish community composition is fundamental to fishery management, research and nature conservation. Estimates of the size distribution, density and biomass of the topmouth gudgeon (Pseudorasbora parva) model species of invasive fish in three ponds were compared among three sampling methods: electrofishing, fish‐trapping and throw‐netting. The study illustrates that the invasive fish, P. parva, can be detected by all tested fishing methods, yet our results clearly showed that there are pronounced differences among methods in population characteristic estimates. Electrofishing and throw‐netting gave biased information on the size distribution of P. parva. Fish‐trapping and throw‐netting gave reasonable P. parva density and biomass estimates, while electrofishing clearly underestimated it. All tested methods showed a body size increment of P. parva between sum...
Biomonitoring of complex heterogeneous environments is highly challenging. Fish in deep water bod... more Biomonitoring of complex heterogeneous environments is highly challenging. Fish in deep water bodies occupy different habitats, therefore a combination of survey methods has traditionally been used. Environmental DNA (eDNA) metabarcoding is a novel monitoring tool that can overcome spatial heterogeneity in a highly sensitive and entirely non-invasive manner. However, taxon detection probability is dependent on real-time environmental variables. In this study, three reservoirs were sampled in two seasons using a spatiotemporally distributed sampling design covering major environmental gradients. In all sampling campaigns, 31 fish taxa were detected which exceeded expectations. Data reliability was confirmed by a tight positive correlation between individual taxon scores derived from gillnet sampling and eDNA site occupancy. Analyses confirmed anticipated trends, such as the highest number of taxa were observed in the largest water body, and more taxa were detected in inflows and littoral regions compared to open water. The most important factors for fish distribution were temperature, age and trophic status (expressed as total Chlorophyll a concentration) of water bodies. Taxon detection reflected ecological niches of individual species, e.g. warm water wels catfish (Silurus glanis) and cold water salmonids. This study provides further evidence that eDNA metabarcoding is suitable for ecological study in heterogeneous environments and may substitute conventional fish sampling techniques.
Intra-species variability in a diet niche, speci cally total niche width (TNW), individual niche ... more Intra-species variability in a diet niche, speci cally total niche width (TNW), individual niche width (INW), and individual specialization (IS), was studied using an innovative approach without sacri cing the animals. Stable isotopes (δ 13 C, δ 15 N) in four body tissues differing in isotopic half-life were analyzed from four freshwater sh species representing different trophic positions. TNW was widest for the apex predator (European cat sh) and narrowest for the obligate predator (Northern pike). INW exhibited a polynomial trend for European cat sh, Northern pike and Eurasian perch (mesopredator), decreasing with body mass and increasing again after exceeding a certain species-dependent body mass threshold. Thus, for ectotherms, apex predator status is linked rather to its size than to the species. In herbivores (rudd), INW increased with body mass. IS of predators negatively correlated with site trophic state. The trends can be generalized to other species at similar trophic positions in either aquatic or terrestrial systems.
1. Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic envi... more 1. Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environment. A general pattern of DVMs has been well described, particularly in European perch (Perca fluviatilis), but whether the migrations are directly controlled by light and what is the ultimate cause of the diel vertical shifts, remains poorly understood. 2. Undertaking a large-scale field experiment in a thermally stratified, canyon-shaped reservoir, we demonstrated for the first time that DVMs of a bathypelagic early juveniles community, dominated by European perch larvae and juveniles prior the metamorphosis, were under direct control of the light intensity; that is, they did not operate as a genetically fixed behaviour. 3. Prior to the experiment, the depth distribution of the bathypelagic perch early juveniles was strongly correlated with the light intensity on the water surface (p < .001). The community underwent regular DVMs between the epilimnion (depth <2.0 m) and hypolimnion (depth >3.0 m) reaching a maximum amplitude of 13 m. 4. Hydroacoustic recordings by the echosounder SIMRAD EK 60 (120 and 400 kHz) showed that during the experiment, when the surface was covered with a large black non-transparent foil (2500 m 2 ; simulated conditions of complete and constant darkness), the regular vertical movement of the bathypelagic perch early juveniles was interrupted and the community occupied the epilimnion constantly for 24 hr. 5. Immediately after the foil was removed at midday, the bathypelagic perch early juveniles were exposed to a steep increase in light intensity (from <1 LUX to >100 9 10 3 LUX) and they escaped into the hypolimnion where they were safe from visual predation which took place in the bright surface layers (epilimnion particularly). Our findings imply that occupying a deep, dark refuge in the daytime is essential for the survival of perch in their early life stage.
Abstract Fish recruitment in riverine reservoirs is not fully understood because the long-term da... more Abstract Fish recruitment in riverine reservoirs is not fully understood because the long-term data series required for standard stock–recruitment models are often lacking. In this study, two unrelated piscivorous species with different ecologies, asp ( Leuciscus aspius ) and pikeperch ( Sander lucioperca ), were investigated over a 14-year period in a reservoir in the Czech Republic using a novel informative statistical approach based on dimension reduction methods. This method is useful for situations in which potential predictors are equal to, or exceed, the length of the time series. Recruitment of asp fry was affected by zooplankton abundance, predator density and temperature. Recruitment of pikeperch fry measured with seine and trawls was only affected by the number of predators, while recruitment of pikeperch fry estimated with gillnet data was also affected by temperature and water level fluctuation. Although gillnets are commonly used sampling method, it seems to be inappropriate for developing fry predicting model. This research also highlights the use of a novel approach to dimension reduction for analysis of factors affecting recruitment using shorter time series (in our case 13 years).
Ligula intestinalis (Linnaeus, 1758) is a tapeworm parasite with a worldwide distribution that us... more Ligula intestinalis (Linnaeus, 1758) is a tapeworm parasite with a worldwide distribution that uses a wide variety of fish species as its second intermediate host. In the present study, we investigated the prevalence and population genetic structure of plerocercoids of L. intestinalis in five common cyprinoid species, roach Rutilus rutilus (Linnaeus), freshwater bream Abramis brama (Linnaeus), white bream Blicca bjoerkna (Linnaeus), bleak Alburnus alburnus (Linnaeus), and rudd Scardinius erythrophthalmus (Linnaeus), collected in six water bodies of the Czech Republic (Milada, Most, Medard, Jordán, Římov and Lipno). Of the six study sites, the highest frequency of parasitism was recorded in Lake Medard (15%). The overall prevalence rate among the species was as follows: roach > rudd ≥ freshwater bream > bleak > white bream. Two mitochondrial genes (cytb and COI) were used to compare the population genetic structure of parasite populations using selected samples from the five fish species. The results of the phylogenetic analysis indicated that all populations of L. intestinalis were placed in Clade A, previously identified as the most common in Europe. At a finer scale, haplotype network and PCoA analyses indicated the possible emergence of host specificity of several mtDNA haplotypes to the freshwater bream. Moreover, pairwise Fixation indices (F ST) revealed a significant genetic structure between the parasite population in freshwater bream and other host species. Parasite populations in roach not only showed the highest rate of prevalence but also depicted a maximum number of shared haplotypes with populations from bleak and rudd. Our results suggest that recent ecological differentiation might have influenced tapeworm populations at a fine evolutionary scale. Thus, the differences in prevalence between fish host species in different lakes might be influenced not only by the parasite's ecology, but also by its genetic diversity.
Structural complexity is known to influence prey behaviour, mortality and population structure, b... more Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake-LSC; high structural complexity-HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent with a prevalent ambush predation behaviour, whereas the higher activity and larger space use in the LSC lake indicated a transition to more active search behaviour. It could lead to increased prey encounter and cause better growth in the LSC lake. Our study demonstrated how differences in structural complexity mediated prominent changes in the foraging behaviour of an apex predator, which in turn may have effects on the prey community.
Fish otoliths are conservative structures that are widely used on fishery science for multiple pu... more Fish otoliths are conservative structures that are widely used on fishery science for multiple purposes. Despite its relevance in the research field, little is known about the ontogeny and inter-population effects on the otolith of freshwater fish. In this study we used otoliths from 1800 European perch (Perca fluviatilis) individuals from 9 different populations to analyze the ontogenetic and interpopulation differences on the otolith shape using six morphometric indices. The relationship between fish and otolith length was fitted using three different regression models (linear, power and logistic) to identify the best allometric relationship. Our results show that there are strong ontogenetic and interpopulation differences in P. fluviatilis otolith shapes. We also show that the relationship between the fish and otolith length follows a logistic curve. The ontogenetic differences on otolith shape might be related to extrinsic factors (diet shift and intra and interspecific competition) in each ecosystem, *Manuscript including abstract Click here to view linked References 2 given that the reservoirs are different and no clear pattern on the otolith shapes can be distinguished among populations. Our results imply that the available back-calculation models may not always provide accurate estimates of P. fluviatilis length and that a model that takes into account the real allometric relationship for the species can improve the fish length estimations of back-calculated fish lengths for the European perch.
Differential use of habitat and prey resources is an important mechanism that may allow coexisten... more Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0-65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.
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Papers by Jiří Peterka