The activities of certain genes as a consequence of exposure to stressors related to typical handling procedures in aquaculture have not been studied in sufficient detail in fish. A stress trial with koi carp was, therefore, conducted, aiming at identifying relevant gene expression patterns in different brain regions during stress responses. The following stressors were selected: tank manipulation, distress caused by exposure to air and eustress due to feed rewards. Responses to these stressors were evaluated 10, 30 and 60 min after their application. The exact determination of gene expression profiles in the carp brain required the comparison of several suitable reference genes, which is also highly recommended for other studies focusing on the fish brain. Moreover, and as expected, the mRNA expression of a number of early immediate genes indicated activity in different brain regions as a response to changes in rearing and experimental conditions. In addition, the mRNA expression of metabolic genes was investigated, since increased brain activity may also increase the metabolic demands of certain brain areas. Furthermore, genes related to the stress axis were included in the study. The mRNA expression patterns of genes belonging to the stress axis revealed that negative stress caused by exposure to air had broad‐ranging effects on the gene regulation patterns in the fish brain, even if the fish were only treated for 1 min. This parallels the effects that have been observed on blood cortisol and glucose. In contrast, a limited number of genes allows discrimination of eustress and distress, which indicates that further research is needed in the future. Finally, the use of different control groups is highly recommended for fish experiments to correct for typical experimental procedures such as lid openings or social isolation.

Our understanding of the timing of stress responses and specific roles of different regulatory pathways that drive stress responses is incomplete. In particular, the regulation of appetite genes as a consequence of exposure to different stressors has not been studied in sufficient detail in fish. Therefore, a stress trial was conducted with koi carp, aiming at identifying typical effects of stress on regulation of appetite genes. The stressors tank manipulation, air exposure and feed rewarding were chosen. The responses to these stressors were evaluated 10, 30 and 60 min after the stressors were applied. Orexigenic and anorexigenic genes were investigated in four different brain regions (telencephalon, hypothalamus, optic tectum and rhombencephalon). The results show that, apart from the typical appetite regulation in the hypothalamus, the different brain regions also display pronounced responses of appetite genes to the different stressors. In addition, several genes in the serotonergic, dopaminergic and gaba-related pathways were investigated. These genes revealed that rearing in pairs of two and opening of the tank lid affected anorexigenic genes, such as cart and cck, which were not changed by air exposure or feed rewarding. Moreover, distress and eustress led to limited, but distinguishable gene expression pattern changes in the investigated brain regions.

Mobbing is an anti-predator strategy initiated by one or more members of prey species aiming at driving away a predator that is not undertaking an attack. Because of a continuous dispute as to whether mobbing of a top predator may indicate species richness, we tested the correlation between the number of species engaging in mobbing and avian community richness. In the boreal forest of central Norway, we conducted a series of 83 bird census trials in 2014 and 2015. Each census trial consisted of two 5-min phases. In the first phase an ordinary point count was performed as a control; in the immediately following second phase either a stuffed Eagle Owl or Capercaillie female decoy was presented to study mobbing of a top avian predator and non-predatory species. Mobbing was more likely to occur, and the number of species that engaged in mobbing was higher, in habitats richer of bird species. Our study showed that the cumulative effects of being mobbed increase with richness of the local avian community. We did not find any support for the notion that mobbing is triggered by mobbing activity of the two most active and abundant species. No support was provided for an assertion that using an owl decoy would result in higher number of detected species during a census. Our study urges the need for identification and quantification of costs of mobbing for an avian predator.

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