Blood viscosity and blood parameters were studied in striped bass, Morone saxatilis (Walbaum) under various fish hatchery conditions. Twenty-seven adult striped bass weighing between 1040 g and 1800 g were divided into four groups: (1) healthy fish; (2) short-term hypoxia, fish exposed to oxygen concentrations of 4 mg/L for four hours; (3) simulated transport, exposed to crowding with oxygen concentrations of approximately 8.4 mg/L; and (4) diseased fish, infected with henneguya causing inflammation of the gill surface leading to hypoxemia in these animals. Plasma and apparent (whole) blood viscosity measurements were made using a Wells-Brookfield cone/plate viscometer at ten different shear rates. At packed cell volumes (PCV) of 30% and 40% and at high shear rates (75 s⁻¹ and 150 s⁻¹) the hypoxic group had a significantly higher apparent blood viscosity when compared to healthy fish, likely the result of a significant increase in the total plasma protein concentration in this group. The diseased group had a significantly higher PCV than all other groups resulting in a significant increase in blood viscosity. No significant difference was observed among the four groups in mean cell volume, mean cell hemoglobin, and mean cell hemoglobin concentration. The increase blood viscosity noted in the hypoxic and diseased groups could lead to a decreased blood flow and oxygen delivery to the tissues.