Skin mucus proteome of gilthead sea bream: A non-invasive method to screen for welfare indicators

• The Top-100 proteins in the skin mucus of gilthead sea bream are analysed.
• Mucus included structural, metabolic and protection proteins.
• Mucosal proteins as targets to characterise physiological status.
• The proteome of epidermal mucus is a tool for non-invasive studies.

In teleosts, the skin mucus is the first physical barrier against physical and chemical attacks. It contains components related to metabolism, environmental influences and nutritional status. Here, we study mucus and composition based on a proteome map of soluble epidermal mucus proteins obtained by 2D-electrophoresis in gilthead sea bream, Sparus aurata. Over 1300 spots were recorded and the 100 most abundant were further analysed by LC-MS/MS and identified by database retrieval; we also established the related specific biological processes by Gene Ontology enrichment. Sixty-two different proteins were identified and classified in 12 GO-groups and into three main functions: structural, metabolic and protection-related. Several of the proteins can be used as targets to determine fish physiological status: actins and keratins, and especially their catabolic products, in the structural functional group; glycolytic enzymes and ubiquitin/proteasome-related proteins in the metabolic functional group; and heat shock proteins, transferrin and hemopexins, in the protection-related group. This study analyses fish mucus, a potential non-invasive tool for characterising fish status, beyond defence capacities, and we postulate some putative candidates for future studies along similar lines.