Arctic charr were allowed to interact in groups of three for 5 days. Skin darkness was quantified by measuring the mean brightness of individual fish before and after social interaction. Brain levels of monoamines and monoamine metabolites and plasma concentrations of cortisol, adrenocorticotropic hormone (ACTH), N-acetyl-(beta)-endorphin and alpha-melanocyte-stimulating hormone (alpha-MSH) were analysed. The results show that social subordination resulted in a significant skin darkening. Furthermore, plasma concentrations of alpha-MSH, ACTH and cortisol were elevated in subordinates, and these fish also displayed elevated levels of 5-hydroxyindoleacetic acid (5-HIAA) in the telencephalon. The ratio of [5-HIAA] to serotonin [5-HT] was increased in several brain areas. In addition, the ratio of 3-methoxy-4-hydroxyphenylglycol (MHPG) to norepinephrine (NE) concentrations was significantly increased in the optic tectum of subordinate fish. Skin darkness following social interaction showed a significant positive correlation with plasma levels of alpha-MSH. Plasma levels of ACTH and alpha-MSH were both positively correlated with that of cortisol. Brain [5-HIAA]/[5-HT] ratios were positively correlated with circulating plasma levels of ACTH, and a similar positive correlation was seen between [MHPG]/[NE] ratios in the optic tectum and plasma levels of ACTH, alpha-MSH and N-acetyl-beta-endorphin. In contrast, hypothalamic [MHPG]/[NE] ratios displayed a negative correlation with plasma alpha-MSH concentrations. The present study demonstrates that social stress induces skin darkening in Arctic charr and that this effect could be mediated by a stress-induced increase in the levels of alpha-MSH in the circulation. Furthermore, the results suggest that 5-HT and NE in the central nervous system could be factors regulating the pituitary release of ACTH and alpha-MSH.
Recognising our community as we approach JEB's centenary
In this Editorial, Craig Franklin, Michaela Handel and Kathryn Knight reflect on recent developments at JEB and acknowledge the support of the community during what has been a particularly challenging year. Looking forward, they discuss the journal’s centenary celebrations in 2023.
Our Transformative Journals have exceeded their OA growth targets
In the field: an interview with Roger Hanlon
Roger Hanlon talks about his fieldwork experiences diving all over the planet to understand cephalopod camouflage and communication.
How climbing parrots achieve pitch stability while ascending
Climbing parrots push and pull with their feet on ladder rungs and push with their tails to prevent themselves from toppling backward as they ascend.
Towards understanding the neural origins of hibernation
Madeleine Junkins, Sviatoslav Bagriantsev and Elena Gracheva review the role of the nervous system in hibernation, arguing that it actively promotes and supports the hibernation process rather than simply enduring it.
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