Fig. 3. Light micrographs of the gills from three different sizes of the obligate air-breathing teleost Arapaima gigas: (A) 10 g, (B) 100 g and (C) 1 kg body mass. C is a micrograph of two neighbouring filaments; note the absence of lamellae and extensive proliferation of mitochondria-rich (MR) cells. Scale bars, 20 µm.