Protein changes as robust signatures of fish chronic stress: a proteomics approach in fish welfare research

Abstract

Background: In order to have a greater understanding of fish welfare, sensitive technological tools, such as proteomics, may assist the aquaculture industry as it allows an unbiased approach for the discovery of potential biomarkers for stress monitoring. Stress is characterized by a cascade of physiological responses that end-up inducing further changes at the whole-animal level that might either increase fitness or impair welfare. Monitorization of this dynamic process, up till now relies on indicators that are only a snapshot of the stress level experienced. Within this scope, using G ilthead seabream ( Sparus aurata ) as model, three chronic stress conditions, namely overcrowding, handling and hypoxia, were employed to evaluate the potential of the fish protein-based adaptations as reliable signatures of chronic stress, in contrast with the commonly used hormonal and metabolic indicators. Results: A large spectrum of biological variation regarding cortisol and glucose levels was observed, which values rose higher in net handled fish. In this sense, a potential pattern of stressor-specificity was evidenced since the magnitude of response and tolerance varied markedly from a permanent (crowding) to a repetitive stressor (handling). Gel-based proteomics analysis of the plasma proteome also revealed that net handled fish had the highest number of differential proteins, compared to the other trials . M ass spectrometric analysis, followed by gene ontology enrichment and protein-protein interaction analyses, characterized those as humoral components of the innate immune system and key elements on the response to stimulus. Conclusions: Overall, this study represents the first screening of more reliable signatures of physiological adaptation to chronic stress in fish, allowing the future development of novel biomarker models to monitor fish welfare.