A novel approach to quantile estimation in multivariate linear regression models with change-poin... more A novel approach to quantile estimation in multivariate linear regression models with change-points is proposed: the change-point detection and the model estimation are both performed automatically, by adopting either the quantile fused penalty or the adaptive version of the quantile fused penalty. These two methods combine the idea of the check function used for the quantile estimation and the L 1 penalization principle known from the signal processing and, unlike some standard approaches, the presented methods go beyond typical assumptions usually required for the model errors, such as sub-Gaussian or Normal distribution. They can effectively handle heavy-tailed random error distributions, and, in general, they offer a more complex view on the data as one can obtain any conditional quantile of the target distribution, not just the conditional mean. The consistency of detection is proved and proper convergence rates for the parameter estimates are derived. The empirical performance is investigated via an extensive comparative simulation study and practical utilization is demonstrated using a real data example.
Detection procedures for a change in means of panel data are proposed. Unlike classical inference... more Detection procedures for a change in means of panel data are proposed. Unlike classical inference tools used for the changepoint analysis in the panel data framework, we allow for mutually dependent and generally non-stationary panels with an extremely short follow-up period. Two competitive self-normalized test statistics are employed and their asymptotic properties are derived for a large number of available panels. The bootstrap extensions are introduced in order to handle such a universal setup. The novel changepoint methods are able to detect a common break point even when the change occurs immediately after the first time point or just before the last observation period. The developed tests are proved to be consistent. Their empirical properties are investigated through a simulation study. The invented techniques are applied to option pricing and non-life insurance.
This paper focuses on market changes due to exogenous effects. The standard implied volatility is... more This paper focuses on market changes due to exogenous effects. The standard implied volatility is shown to be insufficient for a proper detection and analysis of this type of risk. This is mainly because such changes are usually dominated by endogenous effects coming from a specific trading mechanism or a natural market dynamics. A unique methodological approach based on artificial options that always have a constant (over time) maturity is proposed and explicitly defined. The key principle is to use interpolated volatilities that can effectively eliminate instabilities due to the natural market dynamics while the changes caused by the exogenous causes stay preserved. Formal statistical tests for distinguishing significant effects are proposed under different theoretical and practical scenarios. Statistical theory, computational and algorithmic details, and comprehensive empirical comparisons together with a real data illustration are all presented in the paper.
An online changepoint detection procedure based on conditional expectiles is introduced. The key ... more An online changepoint detection procedure based on conditional expectiles is introduced. The key contribution is threefold: nonlinearity of the underlying model improves the overall flexibility while a parametric form of the unknown regression function preserves a simple and straightforward interpretation; The conditional expectiles, well-known in econometrics for being the only coherent and elicitable risk measure, introduce additional robustness—especially with respect to asymmetric error distributions common in various types of data; The proposed statistical test is proved to be consistent and the distribution under the null hypothesis does not depend on the functional form of the underlying model nor the unknown parameters. Empirical properties of the proposed real-time changepoint detection test are investigated in a simulation study and a practical applicability is illustrated using the Covid-19 prevalence data from Prague.
We propose a methodological approach for capturing and analyzing the impacts of investment disput... more We propose a methodological approach for capturing and analyzing the impacts of investment disputes on option markets. A dispute submission typically brings in unspecified uncertainty and additional risk. The implied volatility of options is shown to reflect such effects. However, nontrivial caution and nonstandard statistical techniques are needed to analyze them appropriately. Artificial options with a constant (over time) maturity are introduced to emphasize these effects. A panel data representation of artificial implied volatility smiles is used to ensure the overall model flexibility, transparency, and its practical interpretability. Finally, a stochastically valid changepoint detection procedure is adopted to reveal significant impacts of an investment dispute on the overall riskiness and the stock price evolution. The results show significant impacts of the first tribunal meeting and the first procedural order of the disputes under consideration.
In laboratory experiments, variously colored strains of animals, including those with albino phen... more In laboratory experiments, variously colored strains of animals, including those with albino phenotypes, are commonly used. The melanocortin theory suggests, however, that coloration phenotypes alter animal physiology and behavior. Animals with the albino phenotype show photoreceptor degradation associated with lowered visual accuracy, escape reactions, etc., presumably accompanied by prevailing nocturnal activity and lowered aggressiveness. This assumption was tested in small groups of albino and pigmented European catfish, Silurus glanis, during the diel cycle. The frequency of agonistic interactions was observed during mutual contests for shelters, and subsequently, blood plasma, brain, gill, and liver samples were collected to evaluate stress parameters. In an experimental arena with shelters, the light/dark rhythmicity of locomotor activity and aggressiveness of the two phenotypes were comparable; the peak was observed at night, and a lower peak was observed at dawn. In an expe...
One of the most fundamental tasks in non-life insurance, done on regular basis, is risk reserving... more One of the most fundamental tasks in non-life insurance, done on regular basis, is risk reserving assessment analysis, which amounts to predict stochastically the overall loss reserves to cover possible claims. The most common reserving methods are based on different parametric approaches using aggregated data structured in the run-off triangles. In this paper, we propose a rather non-parametric approach, which handles the underlying loss development triangles as functional profiles and predicts the claim reserve distribution through permutation bootstrap. Three competitive functional-based reserving techniques, each with slightly different scope, are presented; their theoretical and practical advantages – in particular, effortless implementation, robustness against outliers, and wide-range applicability – are discussed. Theoretical justifications of the methods are derived as well. An evaluation of the empirical performance of the designed methods and a full-scale comparison with s...
The main goal of supervised learning is to construct a function from labeled training data which ... more The main goal of supervised learning is to construct a function from labeled training data which assigns arbitrary new data points to one of the labels. Classification tasks may be solved by using some measures of data point centrality with respect to the labeled groups considered. Such a measure of centrality is called data depth. In this paper, we investigate conditions under which depth-based classifiers for directional data are optimal. We show that such classifiers are equivalent to the Bayes (optimal) classifier when the considered distributions are rotationally symmetric, unimodal, differ only in location and have equal priors. The necessity of such assumptions is also discussed.
In this paper, a linear model with grouped explanatory variables is considered. The idea is to pe... more In this paper, a linear model with grouped explanatory variables is considered. The idea is to perform an automatic detection of different successive groups of the unknown coefficients under the assumption that the number of groups is of the same order as the sample size. The standard least squares loss function and the quantile loss function are both used together with the fused and adaptive fused penalty to simultaneously estimate and group the unknown parameters. The proper convergence rate is given for the obtained estimators and the upper bound for the number of different successive group is derived. A simulation study is used to compare the empirical performance of the proposed fused and adaptive fused estimators and a real application on the air quality data demonstrates the practical applicability of the proposed methods.
A novel approach to quantile estimation in multivariate linear regression models with change‐poin... more A novel approach to quantile estimation in multivariate linear regression models with change‐points is proposed: the change‐point detection and the model estimation are both performed automatically, by adopting either the quantile‐fused penalty or the adaptive version of the quantile‐fused penalty. These two methods combine the idea of the check function used for the quantile estimation and the L1 penalization principle known from the signal processing and, unlike some standard approaches, the presented methods go beyond typical assumptions usually required for the model errors, such as sub‐Gaussian or normal distribution. They can effectively handle heavy‐tailed random error distributions, and, in general, they offer a more complex view on the data as one can obtain any conditional quantile of the target distribution, not just the conditional mean. The consistency of detection is proved and proper convergence rates for the parameter estimates are derived. The empirical performance ...
The movement of individuals within preferred areas is reduced by a high availability of food and ... more The movement of individuals within preferred areas is reduced by a high availability of food and information about its distribution, while high number of competitors promotes increased movement. Experienced animals use information about social and physical environment to improve resources exploitation, tended to maintain positions within the preferred areas and reuse the environment that is often referred to as site fidelity. In this study, radio‐telemetry was used to observe the movements of 98 adult brown trout, Salmo trutta, in oligotrophic streams with different population densities; to determine subpopulation site fidelity, 5,195 conspecifics from 14 subpopulations were individually tagged during spring and autumn. During a 7‐year‐long field study, we tested the hypothesis that brown trout individuals from subpopulations with high site fidelity would display lower movement. The hypothesis was supported, and reduced movement was further related to high subpopulation density in a...
Joinpoint regression models are popular in various situations (modeling different trends in econo... more Joinpoint regression models are popular in various situations (modeling different trends in economics, mortality and incidence series or epidemiology studies and clinical trials). The literature on joinpoint regression mostly focuses on either the frequentist point of view, or discusses Bayesian approaches instead. A model selection step in all these scenarios considers only some limited set of alternatives, from which the final model is chosen. We present a different model estimation approach: the final model is selected out of all possible alternatives admitted by the data. We apply the L 1-regularization idea and via the sparsity principle we identify significant joinpoint locations to construct the final model. Some theoretical results and practical examples are given as well.
ABSTRACT Parasitic species can affect host behaviour in various ways. Freshwater mussels of the s... more ABSTRACT Parasitic species can affect host behaviour in various ways. Freshwater mussels of the superfamily Unionoidea have a glochidia larva that is parasitic on fish. Our aim was to evaluate whether fish exposed to glochidia have distinct behaviour that could affect the upstream dispersal of the parasite.Many freshwater mussels are highly endangered, and understanding the relationships with their hosts is important for their conservation. However, research on the behavioural effects of parasitism on fish host activity and/or the upstream dispersal of mussel larvae in nature has received little attention.Specifically, we examined a fish (the chub, Squalius cephalus) that hosts the larval stage of a freshwater bivalve (Anodonta anatina) and investigated alterations in host behaviour induced by the parasite. One laboratory and two field experiments were conducted using passive integrated transponder systems and radio-telemetry.Infected fish were generally less active in the laboratory and, in the field, dispersed less far upstream. Moreover, radio-telemetry revealed a habitat shift by the infected fish, which were found further from the riverbank.We suggest that behavioural changes in the fish that are induced by glochidia do not facilitate the long-distance dispersal of the mussel but rather cause reductions in fish activity and slight habitat shifts. Possible consequences of such behavioural alterations are discussed.
Intercalibration process introduces a complex set of rules and specific tasks (qualitative and qu... more Intercalibration process introduces a complex set of rules and specific tasks (qualitative and quantitative) arising from requirements of the Water Framework Directive (WFD) 2000/60/EC. As a result, one obtains fully harmonized ecological quality boundaries for various biological quality elements (BQE – macro-invertebrates, phytobenthos, macrophytes, phytoplankton and fishes). The boundaries are harmonized among participating member states of the European Union, which are distributed into geographical intercalibration groups (GIGs). The main precondition of the process is to define a set of general principles in a full correspondence with the normative definitions of WFD and to apply them in a well-established sequence of single steps, which are all carefully supervised. The aim of this paper is to offer a systematic and brief overview of the intercalibration process: we list the main steps of the intercalibration exercise and we show their application under the specific conditions ...
Physiological and behavioural constraints hinder albino individuals. Albino animals are rare in t... more Physiological and behavioural constraints hinder albino individuals. Albino animals are rare in the wild; this trait is associated with easy detection by predators, non-native or damaged environments, and exclusively aphotic environments in total darkness. The social aspect of albinism is reported only for human beings, and the effect is distinguishable in time and space when social benefits, are used to a limited the extent. Thus far, the social consequences of albinism for animals remain unknown. We used socially established groups of the pigmented catfish, (Silurus glanis), to observe space and temporal distance detachment of albino specimens in laboratory conditions. The albino fish were separated at larger distances from the group than pigmented individuals with the same social status determined by familiarity, and this asymmetry also varied in time. Albinism-related ostracism results in a solitary existence, usually followed by enhanced predation risk. The motivation for an individual's exclusion from a group appears to be the avoidance of the predation risk that increases not only for an odd individual but also for conspecifics within a group. Our findings indicate a role for albinism in behavioural processes related to sociality in a group of conspecifics.
ABSTRACT Within aquaculture systems, shelters are often used to reduce cannibalism, minimise ener... more ABSTRACT Within aquaculture systems, shelters are often used to reduce cannibalism, minimise energy consumption, accelerate the start of exogenous feeding, support growth, and improve survival and welfare. However, stronger competition for shelters in aquaculture systems relative to that under wild conditions may result in a higher level of aggressiveness accompanied by an increase in energy consumption. Furthermore, fish stress can increase when unfamiliar conspecifics are introduced during fish farming. Agonistic behaviours, however, can be decreased by familiarity established based on the repeated contact of individuals. Under laboratory conditions, we observed the behaviour of two unfamiliar groups of juvenile 0+ European catfish. To study the spatial preferences of fish, we used passive integrated transponders, and we tested the hypothesis that familiarity would be a key factor affecting shelter occupancy if the number of shelters was less than the number of conspecifics. The results showed that the catfish preferred the shelter area. Conspecifics maintained the groups that were formed prior to mixing and displayed a tendency to control limited resources. This behaviour was indicated by the odds ratio for occupying the shelter vs. remaining in the original area of the familiar group, with a majority of familiar specimens being present in the shelter area. The logarithm of this odds ratio increased over time and reached the highest value at the end of the experiment, indicating there was a slightly greater than 9-fold higher likelihood of choosing a shelter in the presence of a familiar majority. The results presented herein indicate that available resources are primarily used on the basis of familiarity.
In keeping with the requirements of the Water Framework Directive (2000/60/EC) a national approac... more In keeping with the requirements of the Water Framework Directive (2000/60/EC) a national approach to ecological status assessment using benthic macorinvertebrates has been proposed. The method can be applied only to the samples which had been taken and processed according to the Czech Standard 75 7701 (PERLA) and is, therefore, designed to evaluate wadable streams and rivers on the basis of multihabitat benthic macroinvertebrate samples of standard size taken at an appropriate site under normal hydrological conditions. Multimetric index has been derived for 6 wider stream types determined on the basis of stream size and altitude categories. It is composed of 6 to7 differently weighted metrics and B index that is calculated by prediction model PERLA. Presented method has been successfully subjected to the intercalibration exercise in Central Baltic and Eastern Continental Geographical Intercalibration Groups.
A novel approach to quantile estimation in multivariate linear regression models with change-poin... more A novel approach to quantile estimation in multivariate linear regression models with change-points is proposed: the change-point detection and the model estimation are both performed automatically, by adopting either the quantile fused penalty or the adaptive version of the quantile fused penalty. These two methods combine the idea of the check function used for the quantile estimation and the L 1 penalization principle known from the signal processing and, unlike some standard approaches, the presented methods go beyond typical assumptions usually required for the model errors, such as sub-Gaussian or Normal distribution. They can effectively handle heavy-tailed random error distributions, and, in general, they offer a more complex view on the data as one can obtain any conditional quantile of the target distribution, not just the conditional mean. The consistency of detection is proved and proper convergence rates for the parameter estimates are derived. The empirical performance is investigated via an extensive comparative simulation study and practical utilization is demonstrated using a real data example.
Detection procedures for a change in means of panel data are proposed. Unlike classical inference... more Detection procedures for a change in means of panel data are proposed. Unlike classical inference tools used for the changepoint analysis in the panel data framework, we allow for mutually dependent and generally non-stationary panels with an extremely short follow-up period. Two competitive self-normalized test statistics are employed and their asymptotic properties are derived for a large number of available panels. The bootstrap extensions are introduced in order to handle such a universal setup. The novel changepoint methods are able to detect a common break point even when the change occurs immediately after the first time point or just before the last observation period. The developed tests are proved to be consistent. Their empirical properties are investigated through a simulation study. The invented techniques are applied to option pricing and non-life insurance.
This paper focuses on market changes due to exogenous effects. The standard implied volatility is... more This paper focuses on market changes due to exogenous effects. The standard implied volatility is shown to be insufficient for a proper detection and analysis of this type of risk. This is mainly because such changes are usually dominated by endogenous effects coming from a specific trading mechanism or a natural market dynamics. A unique methodological approach based on artificial options that always have a constant (over time) maturity is proposed and explicitly defined. The key principle is to use interpolated volatilities that can effectively eliminate instabilities due to the natural market dynamics while the changes caused by the exogenous causes stay preserved. Formal statistical tests for distinguishing significant effects are proposed under different theoretical and practical scenarios. Statistical theory, computational and algorithmic details, and comprehensive empirical comparisons together with a real data illustration are all presented in the paper.
An online changepoint detection procedure based on conditional expectiles is introduced. The key ... more An online changepoint detection procedure based on conditional expectiles is introduced. The key contribution is threefold: nonlinearity of the underlying model improves the overall flexibility while a parametric form of the unknown regression function preserves a simple and straightforward interpretation; The conditional expectiles, well-known in econometrics for being the only coherent and elicitable risk measure, introduce additional robustness—especially with respect to asymmetric error distributions common in various types of data; The proposed statistical test is proved to be consistent and the distribution under the null hypothesis does not depend on the functional form of the underlying model nor the unknown parameters. Empirical properties of the proposed real-time changepoint detection test are investigated in a simulation study and a practical applicability is illustrated using the Covid-19 prevalence data from Prague.
We propose a methodological approach for capturing and analyzing the impacts of investment disput... more We propose a methodological approach for capturing and analyzing the impacts of investment disputes on option markets. A dispute submission typically brings in unspecified uncertainty and additional risk. The implied volatility of options is shown to reflect such effects. However, nontrivial caution and nonstandard statistical techniques are needed to analyze them appropriately. Artificial options with a constant (over time) maturity are introduced to emphasize these effects. A panel data representation of artificial implied volatility smiles is used to ensure the overall model flexibility, transparency, and its practical interpretability. Finally, a stochastically valid changepoint detection procedure is adopted to reveal significant impacts of an investment dispute on the overall riskiness and the stock price evolution. The results show significant impacts of the first tribunal meeting and the first procedural order of the disputes under consideration.
In laboratory experiments, variously colored strains of animals, including those with albino phen... more In laboratory experiments, variously colored strains of animals, including those with albino phenotypes, are commonly used. The melanocortin theory suggests, however, that coloration phenotypes alter animal physiology and behavior. Animals with the albino phenotype show photoreceptor degradation associated with lowered visual accuracy, escape reactions, etc., presumably accompanied by prevailing nocturnal activity and lowered aggressiveness. This assumption was tested in small groups of albino and pigmented European catfish, Silurus glanis, during the diel cycle. The frequency of agonistic interactions was observed during mutual contests for shelters, and subsequently, blood plasma, brain, gill, and liver samples were collected to evaluate stress parameters. In an experimental arena with shelters, the light/dark rhythmicity of locomotor activity and aggressiveness of the two phenotypes were comparable; the peak was observed at night, and a lower peak was observed at dawn. In an expe...
One of the most fundamental tasks in non-life insurance, done on regular basis, is risk reserving... more One of the most fundamental tasks in non-life insurance, done on regular basis, is risk reserving assessment analysis, which amounts to predict stochastically the overall loss reserves to cover possible claims. The most common reserving methods are based on different parametric approaches using aggregated data structured in the run-off triangles. In this paper, we propose a rather non-parametric approach, which handles the underlying loss development triangles as functional profiles and predicts the claim reserve distribution through permutation bootstrap. Three competitive functional-based reserving techniques, each with slightly different scope, are presented; their theoretical and practical advantages – in particular, effortless implementation, robustness against outliers, and wide-range applicability – are discussed. Theoretical justifications of the methods are derived as well. An evaluation of the empirical performance of the designed methods and a full-scale comparison with s...
The main goal of supervised learning is to construct a function from labeled training data which ... more The main goal of supervised learning is to construct a function from labeled training data which assigns arbitrary new data points to one of the labels. Classification tasks may be solved by using some measures of data point centrality with respect to the labeled groups considered. Such a measure of centrality is called data depth. In this paper, we investigate conditions under which depth-based classifiers for directional data are optimal. We show that such classifiers are equivalent to the Bayes (optimal) classifier when the considered distributions are rotationally symmetric, unimodal, differ only in location and have equal priors. The necessity of such assumptions is also discussed.
In this paper, a linear model with grouped explanatory variables is considered. The idea is to pe... more In this paper, a linear model with grouped explanatory variables is considered. The idea is to perform an automatic detection of different successive groups of the unknown coefficients under the assumption that the number of groups is of the same order as the sample size. The standard least squares loss function and the quantile loss function are both used together with the fused and adaptive fused penalty to simultaneously estimate and group the unknown parameters. The proper convergence rate is given for the obtained estimators and the upper bound for the number of different successive group is derived. A simulation study is used to compare the empirical performance of the proposed fused and adaptive fused estimators and a real application on the air quality data demonstrates the practical applicability of the proposed methods.
A novel approach to quantile estimation in multivariate linear regression models with change‐poin... more A novel approach to quantile estimation in multivariate linear regression models with change‐points is proposed: the change‐point detection and the model estimation are both performed automatically, by adopting either the quantile‐fused penalty or the adaptive version of the quantile‐fused penalty. These two methods combine the idea of the check function used for the quantile estimation and the L1 penalization principle known from the signal processing and, unlike some standard approaches, the presented methods go beyond typical assumptions usually required for the model errors, such as sub‐Gaussian or normal distribution. They can effectively handle heavy‐tailed random error distributions, and, in general, they offer a more complex view on the data as one can obtain any conditional quantile of the target distribution, not just the conditional mean. The consistency of detection is proved and proper convergence rates for the parameter estimates are derived. The empirical performance ...
The movement of individuals within preferred areas is reduced by a high availability of food and ... more The movement of individuals within preferred areas is reduced by a high availability of food and information about its distribution, while high number of competitors promotes increased movement. Experienced animals use information about social and physical environment to improve resources exploitation, tended to maintain positions within the preferred areas and reuse the environment that is often referred to as site fidelity. In this study, radio‐telemetry was used to observe the movements of 98 adult brown trout, Salmo trutta, in oligotrophic streams with different population densities; to determine subpopulation site fidelity, 5,195 conspecifics from 14 subpopulations were individually tagged during spring and autumn. During a 7‐year‐long field study, we tested the hypothesis that brown trout individuals from subpopulations with high site fidelity would display lower movement. The hypothesis was supported, and reduced movement was further related to high subpopulation density in a...
Joinpoint regression models are popular in various situations (modeling different trends in econo... more Joinpoint regression models are popular in various situations (modeling different trends in economics, mortality and incidence series or epidemiology studies and clinical trials). The literature on joinpoint regression mostly focuses on either the frequentist point of view, or discusses Bayesian approaches instead. A model selection step in all these scenarios considers only some limited set of alternatives, from which the final model is chosen. We present a different model estimation approach: the final model is selected out of all possible alternatives admitted by the data. We apply the L 1-regularization idea and via the sparsity principle we identify significant joinpoint locations to construct the final model. Some theoretical results and practical examples are given as well.
ABSTRACT Parasitic species can affect host behaviour in various ways. Freshwater mussels of the s... more ABSTRACT Parasitic species can affect host behaviour in various ways. Freshwater mussels of the superfamily Unionoidea have a glochidia larva that is parasitic on fish. Our aim was to evaluate whether fish exposed to glochidia have distinct behaviour that could affect the upstream dispersal of the parasite.Many freshwater mussels are highly endangered, and understanding the relationships with their hosts is important for their conservation. However, research on the behavioural effects of parasitism on fish host activity and/or the upstream dispersal of mussel larvae in nature has received little attention.Specifically, we examined a fish (the chub, Squalius cephalus) that hosts the larval stage of a freshwater bivalve (Anodonta anatina) and investigated alterations in host behaviour induced by the parasite. One laboratory and two field experiments were conducted using passive integrated transponder systems and radio-telemetry.Infected fish were generally less active in the laboratory and, in the field, dispersed less far upstream. Moreover, radio-telemetry revealed a habitat shift by the infected fish, which were found further from the riverbank.We suggest that behavioural changes in the fish that are induced by glochidia do not facilitate the long-distance dispersal of the mussel but rather cause reductions in fish activity and slight habitat shifts. Possible consequences of such behavioural alterations are discussed.
Intercalibration process introduces a complex set of rules and specific tasks (qualitative and qu... more Intercalibration process introduces a complex set of rules and specific tasks (qualitative and quantitative) arising from requirements of the Water Framework Directive (WFD) 2000/60/EC. As a result, one obtains fully harmonized ecological quality boundaries for various biological quality elements (BQE – macro-invertebrates, phytobenthos, macrophytes, phytoplankton and fishes). The boundaries are harmonized among participating member states of the European Union, which are distributed into geographical intercalibration groups (GIGs). The main precondition of the process is to define a set of general principles in a full correspondence with the normative definitions of WFD and to apply them in a well-established sequence of single steps, which are all carefully supervised. The aim of this paper is to offer a systematic and brief overview of the intercalibration process: we list the main steps of the intercalibration exercise and we show their application under the specific conditions ...
Physiological and behavioural constraints hinder albino individuals. Albino animals are rare in t... more Physiological and behavioural constraints hinder albino individuals. Albino animals are rare in the wild; this trait is associated with easy detection by predators, non-native or damaged environments, and exclusively aphotic environments in total darkness. The social aspect of albinism is reported only for human beings, and the effect is distinguishable in time and space when social benefits, are used to a limited the extent. Thus far, the social consequences of albinism for animals remain unknown. We used socially established groups of the pigmented catfish, (Silurus glanis), to observe space and temporal distance detachment of albino specimens in laboratory conditions. The albino fish were separated at larger distances from the group than pigmented individuals with the same social status determined by familiarity, and this asymmetry also varied in time. Albinism-related ostracism results in a solitary existence, usually followed by enhanced predation risk. The motivation for an individual's exclusion from a group appears to be the avoidance of the predation risk that increases not only for an odd individual but also for conspecifics within a group. Our findings indicate a role for albinism in behavioural processes related to sociality in a group of conspecifics.
ABSTRACT Within aquaculture systems, shelters are often used to reduce cannibalism, minimise ener... more ABSTRACT Within aquaculture systems, shelters are often used to reduce cannibalism, minimise energy consumption, accelerate the start of exogenous feeding, support growth, and improve survival and welfare. However, stronger competition for shelters in aquaculture systems relative to that under wild conditions may result in a higher level of aggressiveness accompanied by an increase in energy consumption. Furthermore, fish stress can increase when unfamiliar conspecifics are introduced during fish farming. Agonistic behaviours, however, can be decreased by familiarity established based on the repeated contact of individuals. Under laboratory conditions, we observed the behaviour of two unfamiliar groups of juvenile 0+ European catfish. To study the spatial preferences of fish, we used passive integrated transponders, and we tested the hypothesis that familiarity would be a key factor affecting shelter occupancy if the number of shelters was less than the number of conspecifics. The results showed that the catfish preferred the shelter area. Conspecifics maintained the groups that were formed prior to mixing and displayed a tendency to control limited resources. This behaviour was indicated by the odds ratio for occupying the shelter vs. remaining in the original area of the familiar group, with a majority of familiar specimens being present in the shelter area. The logarithm of this odds ratio increased over time and reached the highest value at the end of the experiment, indicating there was a slightly greater than 9-fold higher likelihood of choosing a shelter in the presence of a familiar majority. The results presented herein indicate that available resources are primarily used on the basis of familiarity.
In keeping with the requirements of the Water Framework Directive (2000/60/EC) a national approac... more In keeping with the requirements of the Water Framework Directive (2000/60/EC) a national approach to ecological status assessment using benthic macorinvertebrates has been proposed. The method can be applied only to the samples which had been taken and processed according to the Czech Standard 75 7701 (PERLA) and is, therefore, designed to evaluate wadable streams and rivers on the basis of multihabitat benthic macroinvertebrate samples of standard size taken at an appropriate site under normal hydrological conditions. Multimetric index has been derived for 6 wider stream types determined on the basis of stream size and altitude categories. It is composed of 6 to7 differently weighted metrics and B index that is calculated by prediction model PERLA. Presented method has been successfully subjected to the intercalibration exercise in Central Baltic and Eastern Continental Geographical Intercalibration Groups.
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Papers by Matus Maciak