The ability of x-cell affected fish to swim was determined using a swimming tunnel closed box respirometer and measuring maximum oxygen consumption and recovery post exercise. In severe cases of x-cell disease infection, fish are chronically hypertensive. The extent of hypertension was assessed by measuring dorsal and ventral aortae blood pressures, heart rate and determination of oxygen tensions ... of the blood. ECG electrodes also allowed measurements of the function of the heart, while filtering the signal allowed simultaneous measurements of ventilation. How the disease affects oxygen uptake and transport was assessed by measuring blood oxygen tension and distribution of blood through the gills. In addition, samples of the heart were collected for morphometric work on the heart to allow a quantitative determination of how the hypertension has affected its structure.