Individualities mediate divergent stress responses and appetite regulation in CNS of olive flounder, Paralichthys olivaceus

In farmed animals, individualities have demonstrated links to health and welfare. However, differential modu-lation of orexigenic, anorexigenic neuroendocrine and endocrine factors in different individuals with different individualities remain unclear. Therefore, we investigated the contribution of the hypothalamic-pituitary-interrenal (HPI), anorexigenic and orexigenic signal molecules to the regulation of appetite in different in-dividuals of adult olive flounder exposed to social isolation stress. We employed behavior assays to separate flounder into three behavioural types (proactive-14%, intermediate-30% and reactive-56%). We found marked elevation in plasma corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and cortisol, and a stronger suppression of feeding post-stress in reactive than other groups. Reactive also had significantly higher CRH and urotensin (UI) mRNA levels in the preoptic area, hypothalamus, hind brain, spinal cord and caudal neurosecretory system (CNSS) than the rest of the groups. Similarly, brain anorexigenic cholecystokinin (CCK), serotonin (5-HT1A) and glucocorticoid receptor (GR) mRNA levels in the preoptic area, telencephalon, hypothalamus, hind brain and CNSS were all higher in reactive than other groups. Contrary, reactive had lower neuropeptide Y (NPY), ghrelin and prolactin mRNA levels in the preoptic area, telencephalon, hypothalamus and CNSS than other groups. There was no significant difference between proactive and intermediate in all measured parameters. Overall, the results demonstrate that social isolation stress is differentially modulated in different individuals and those CRH-related peptides, anorexigenic and orexigenic signalling molecules contribute to divergent stress response and regulation of appetite in P. olivaceus.