Morphometric partitioning of the respiratory surface area and diffusion capacity of the gills and swim bladder in juvenile Amazonian air-breathing fish, Arapaima gigas

► The respiratory organs of Arapaima gigas were evaluate using stereological methods. ► Swim bladder surface area exceeded that of the gills by a factor of 2.79. ► Swim bladder morphometric diffusing capacity was greater than in the gills. ► Low gill morphometric diffusion capacity restricts O2 uptake.