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 (Oncorhynch us mykiss) acclimated to hyperoxic (130%), normoxic (100%), or hypoxic (65%) dissolved oxygen concentrations for 10 weeks. Acclimation to su persaturated dissolved oxygen resulted in lower blood haemoglobin, hae matocrit, and total red blood cell concentration. Within 6 h of a conf inement challenge in their respective oxygen regime, fish acclimated t o 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 condit ions which acclimatized to the confinement stress. The stress of the c hallenge imposed an oxygen demand that was met by separate compensator y strategies to increase oxygen-carrying capacity in the blood. Hypero xic and hypoxic fish utilized cellular swelling as evidenced by the in crease in mean corpuscular volume, and normoxic fish responded with ce llular recruitment as evidence by the increase in total red blood cell concentration. The implication of supplemental dissolved oxygen usage in intensive aquaculture is discussed.