Molecular regulation of chronic stress responses in European sea bass, .

INTRODUCTION

This study examines the effects of predictable repeated chronic stress on the stress response and cortisol metabolism in European sea bass.

METHODS

Fish were exposed to daily stress for 11 days and sampled the next day before or after an additional stressor. Chronically stressed fish showed an attenuated acute cortisol response and altered circulating cortisone levels.

RESULTS AND DISCUSSION

Gene expression analyses revealed stress-induced regulatory changes. In the brain, and mRNA expression was affected by chronic stress, while c by acute stress. In the head kidney, was affected by both stress types, whereas and responded only to acute stress. Neither , encoding the ACTH receptor, nor , responsible for cortisol inactivation, were affected. In the liver, and were upregulated under chronic stress, suggesting an adaptive mechanism to regulate cortisol metabolism. In contrast, gill receptor expression remained largely unchanged, except for acute stress-induced , , and downregulation in chronically stressed fish, potentially modulating cortisol signaling. These findings suggest that chronic stress alters neuroendocrine regulation, desensitizing the HPI axis and impairing the acute stress response. Understanding these mechanisms provides insights into chronic stress adaptation in fish, with implications for aquaculture and stress physiology research.