Animals that are exposed to a stressor enter in a state of emergency. The response to acute stress consists of a set of physiological and behavioural changes that aims to keep the allostatic balance of the animal and maximize survival. In this condition the body activates a series of adaptive processes. The brain, after the recognition of a real or perceived threat, initiates the response integrating several factors like experience, memories, expectation, and re-evaluation of needs in anticipation of physiological requirements. As primary response, the sympathetic nerve fibres, which innervate the chromaffin cells, trigger the release of catecholamines via cholinergic receptors. Because catecholamines are stored in the chromaffin cells, their release following stress is rapid and the circulating levels of these hormones increase immediately with stress.</p><p>Here we describe changes and the timing of the stress response of freshwater Atlantic salmon after being exposed to a strong acute stressor, consisting on netting all fish from their holding tanks and , transfer to new holding tanks. The fish were sampled sequentially (plasma ACTH, cortisol, metabolites, mucus cortisol and head kidney for transcriptomics) to obtain a time-course response. Subgroups of fish were also subjected to the same stressor ring them in a common transport tank and their redistribution in new tanks until being sampled at different time points. Finally, a group of fish will be subjected to the same stressor for a second time to assess their capacity to respond the same challenge again within a short timeframe. to a new challenge in a relatively short time. By sampling salmon parr at several time points post-stress we will attempt to unravel the dynamic changes on plasma levels of ACTH and cortisol hormones, plasma metabolites and mucus cortisol levels. We will also attempt to display the main transcriptome pathways modulated follow acute stress. The manuscript gives We believe that this study will add new insight on the for all the researcher that study mechanisms of stress response in Atlantic salmon and could form the basis for particularly a useful guideline for sampling protocol.