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Prague, Czech Republic

Slavik O.,Water Research Institution Tgm Prague | Horky P.,Water Research Institution Tgm Prague
Journal of Fish Biology | Year: 2012

Twenty individuals of the largest European freshwater predator, the European catfish Silurus glanis, were tagged with electromyogram (EMG) physiological telemetry sensors. The fish were observed during diel cycles during the spring and summer in the Elbe and Berounka Rivers, Czech Republic. The purpose of this study was to determine whether diel dualism in the activity of S. glanis occurs naturally or is induced by the laboratory environment and by the conditions occurring in aquaculture. The results obtained from the riverine environment tended to show dualism in the use of the light and dark phases of the day because 35% of the individuals varied from a site-specific common diel activity pattern. The EMG values increased in accordance with the mass (M) of the fish. To eliminate the influence of M on individual energy consumption, the EMG records were analysed in terms of the EMG:M ratios. High individual variability was found in these ratios. The diel activity pattern of the individuals with relatively high energy consumption differed from the common diel activity pattern. In contrast, the fish that adopted the common diel activity pattern displayed relatively low energy consumption. The results of this study indicated that dualism and energy consumption are related. The EMG values also varied with the values of the environmental variables. Increasing temperature was associated with high EMG values, whereas the EMG values decreased with increasing flow. © 2012 The Fisheries Society of the British Isles. Source

Slavik O.,Water Research Institution Tgm Prague | Maciak M.,Water Research Institution Tgm Prague | Horky P.,Water Research Institution Tgm Prague
Applied Animal Behaviour Science | Year: 2012

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. © 2012 Elsevier B.V. Source

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