Changes in muscle and blood plasma proteomes of Atlantic salmon (Salmo salar) induced by crowding

Crowding is a well-known stressor for fish and may, depending on its severity and duration, induce several physiological changes to the organisms. The present work aimed to identify changes in muscle and blood plasma proteomes of Atlantic salmon induced by crowding (> 200 kg fish/m3, 40 min). A total of 27 and 17 proteins showed altered abundance in muscle and blood plasma, respectively, from control and crowded salmon. The main changes in muscle were related to structural proteins (actin, myosin heavy and light chains, tropomyosin) and enzymes involved in energy production (creatine kinase, enolase, phosphoglycerate kinase), while apolipoprotein A-I, angiotensinogen and complement component C3 were found to change in the blood plasma. All these proteins are involved in different secondary and tertiary stress responses, including altered energy metabolism, osmotic regulation and immune function. The changes observed in energy metabolism indicated a shift towards anaerobic energy production. Moreover, the changes observed in proteins of the immune system indicate that short-term exposure to crowding may induce changes in the immune system of salmon. In conclusion, the changes observed in muscle and blood plasma proteomes not only correspond with the physiological stress response in fish, but also highlights the mechanisms causing an accelerated muscle pH decline and rigor mortis contraction in crowded salmon.