Fig. 1. (a-f) Scanning electron micrographs from the second gill arch of crucian carp and goldfish kept at different temperatures. At 15°C (a) and 20°C (b) the crucian carp gills do not have protruding lamellae. However, after respirometry at 20°C (c) crucian carp gill filament exhibited protruding lamellae, a response probably induced by the hypoxic period in the respirometer. At 25°C (d) the crucian carp developed protruding lamellae in normoxia. Goldfish gills at 15°C (e) showed protruding lamellae; however after 5 days at 7.5°C (f) the gill morphology of goldfish started to resemble that of normoxic crucian carp at 10-20°C. Scale bar, 50 µm.