Structural and circulatory responses to hypoxia in the secondary lamellae ofSalmo gairdneri gills at two temperatures

The first gill arch ofSalmo gairdneri was fixed from normoxic (O2 saturation of the water >90%) and hypoxic (O2 saturation 25–30% for 5 days) fish at 10 °C and 18 °C, and from fish after one-day recovery from hypoxia at 18 °C. The secondary lamellae of the gills were analysed with morphometric methods for structural, haemotological and circulatory changes. During hypoxia a marked vascular distension took place at both temperatures. At both temperatures the vascular distension coincided with a shortening of the diffusion distance (36% at 10 °C and 21% at 18 °C) and a swelling of the erythrocytes (60% at 10 °C and 42% at 18 °C). The effects of these changes on the oxygen uptake of the gills are discussed.