Fig. 2. (A,B) Light micrographs of gills from crucian carp kept in normoxic (A) or hypoxic (B) water at 8°C. Note that the lamellae are present in both conditions but that a regression of the interlamellar cell mass (ILCM) during hypoxia makes the lamellae protrude, thereby greatly increasing the respiratory surface area. A filament arteriole (with blood clots) is seen running vertically in the center of each micrograph. Scale bar, 50 µm (from Sollid et al., 2003).