Fig. 5. Ultrastructure of the filament epithelial cells in normoxic control carp viewed by scanning electron microscopy (SEM; A), and transmission electron microscopy (TEM; B–E). A is the surface of the filament epithelium possessing the `wavy-convex' MRCs with highly ramified microvilli (white arrows) and short and slightly branched microvilli (white-headed arrows), PVCs with complex patterns of microvilli, and a few MCs discharging secretory granules. B is the apical surface of an MRC with highly ramified microvilli, C is the apical surface of an MRC with short microvilli, D is the perinuclear area of an - (`light') MRC, and E is the perinuclear area of a β- (`dark') MRC. M, mitochondrion; MC, mucous cell; McV, microvilli; MRC, mitochondria-rich cell; MV, microvesicle; N, nucleus; PVC, pavement cell; RER, rough endoplasmic reticulum; TR, tubular reticulum. Scale bars: (A) 10 µm; (B,C) 1 µm; (D,E) 0.5 µm.