PHYSIOLOGICAL AND HEMATOLOGICAL RESPONSES IN RAINBOW-TROUT SUBJECTED TO SUPPLEMENTAL DISSOLVED-OXYGEN IN FISH CULTURE

Growth and food conversion did not differ in rainbow trout (Oncorhynchus mykiss) acclimated to hyperoxic (130%), normoxic (100%), or hypoxic (65%) dissolved oxygen concentrations for 10 weeks. Acclimation to supersaturated dissolved oxygen resulted in lower blood haemoglobin, haematocrit, and total red blood cell concentration. Within 6 h of a confinement challenge in their respective oxygen regime, fish acclimated to 10 weeks of hyperoxic and hypoxic dissolved oxygen exhibited similar stress responses in duration and magnitude (plasma cortisol, glucose, osmolality, blood lactate) compared to fish in normoxic oxygen conditions which acclimatized to the confinement stress. The stress of the challenge imposed an oxygen demand that was met by separate compensatory strategies to increase oxygen-carrying capacity in the blood. Hyperoxic and hypoxic fish utilized cellular swelling as evidenced by the increase in mean corpuscular volume, and normoxic fish responded with cellular recruitment as evidence by the increase in total red blood cell concentration. The implication of supplemental dissolved oxygen usage in intensive aquaculture is discussed.