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An active preference for higher temperatures within a physiological optimum is beneficial for animal movement. For example, ascending temperatures induce an increase in cyprinid fish metabolism and swimming ability. Spring upstream migrations driven by the search for resources may be related to these increases. Conversely, downstream migrations in autumn follow a decrease in temperature. When fish migrations are driven by a search for resources, for example, food availability and reproduction, or to avoid predators, then the temperature effect can be reduced to approximately the threshold temperatures that induce up‐ and/or downstream movement. To test this assumption, we tracked the seasonal migrations of the common bream Abramis brama between a reservoir and its tributary using radio tags with temperature sensors during a 5‐year period. Upstream migrations of the species into the tributary were not motivated by seeking temperatures different from those in the reservoir, that is, fish body temperatures in both environments were comparable across seasons. However, for long‐distance migrations, increasing temperature did support upstream migrations. Temperature did not determine the direction or intensity of short‐distance migration of the species between the reservoir and the tributary. No significant influence of temperature was recorded for the downstream migrations according to the results of the generalised additive mixed model (GAMM1), which related movement distance as the explanatory variable to the signed fish body temperature as the response. The second model (GAMM2) relating fish body temperature as the explanatory variable to the signed movement distance as the response obtained a threshold value of 19.1°C for the upstream migrations and 1.5°C for the downstream migrations of the common bream. [ABSTRACT FROM AUTHOR]

Owing to their widespread use, pharmaceuticals have become important pollutants of the aquatic environment. Pharmaceuticals and parasites can affect the immunity, physiology and behaviour of target organisms, both singly and through interaction. In this study, we related pharmaceutical concentration, parasite infection and condition in brown trout (Salmo trutta m. fario) collected at localities upstream and downstream of a sewage treatment plant (STP). The sites were separated by a weir preventing fish migration. Pharmaceutical number and concentrations differed significantly between sites. Antibiotics and antidepressants were found at the highest concentrations at both localities. Though fish condition and overall parasite abundance did not differ between sites, there was a significant difference in parasite community composition. A higher abundance of monogenean ectoparasites, along with a lower abundance of endoparasites, was observed at the downstream locality. The adverse effect of pharmaceutical load on ecto- and endoparasitic species on brown trout was further confirmed at the individual level using multivariate analysis. Both the number and concentration of pharmaceuticals in fish tissues reflected their high incidence in the environment, confirming the ability of trout to bioaccumulate pharmaceuticals. This could have important consequences on fish health, particularly in small streams where STP effluent represents a high proportion of stream flow. [ABSTRACT FROM AUTHOR]

The introduction of non-native species and human-altered habitats are currently the main threats to freshwater ecosystems. Due to predation and competition, biological invaders can cause extinctions and imperil the status of native species, and this phenomenon is enhanced by habitat alteration, for example, dam construction. In addition to river fragmentation caused by dam construction, the impact of non-native species migrating from reservoirs on native assemblages in their tributaries should be considered from a long-term perspective. The present study focused on asp (Leuciscus aspius), an artificially introduced piscivorous cyprinid that became established in the Lipno Reservoir (Czech Republic). Asp regularly occur in a tributary, the Vltava River, where twenty-five individuals were captured, radio-tagged, and tracked for five consecutive years. Asp occurrence in the tributary was highest during spring due to the upstream migration of spawning fish, and this was interconnected with a movement activity peak in March when the temperature reached 6 °C. The fish migrated a maximum distance of 31 km, and the probability of asp occurrence in the tributary was sex-dependent, with more females than males. Some individuals occupied the Vltava River not only for spawning but remained until the temperatures dropped below 10 °C. This study shows how non-native predators use reservoirs for wintering but feed and spawn in tributaries. [ABSTRACT FROM AUTHOR]