Hypoxic water had 5 mg/L of Dissolved Oxygen (DO) and normoxic water had 11.5 mg/L DO. 40 immature rainbow trout (about 100 g) were housed for 7 days under these conditions (20 fish in each treatment). Then fish were anesthetized with 100 mg/L MS-222, and blood was sampled using caudal puncture with heparinized syringes. The blood was centrifuged at 10 000 x g for 4 minutes in Heraeus Fresco 21 centrifuge (Thermo Fisher). Plasma was removed from this using a pipette, and placed in cryotubes, flash frozen in liquid nitrogen, and then stored at -80oC until preparation for proteomic analysis.