Fig. 2. General view of the scaleless carp gill filaments viewed by light microscopy (LM) in fish exposed to normoxia (control; A), following exposure to 0.3 mg O₂ l^–1 hypoxia for 12 h (B), 24 h (C), and following 12 h recovery in normoxia (D). Note that in A, the filament is thick and there is an interlamellar mass, in B and C there is a thinning of the filament and lamellar epithelium, and protrusion of the lamellae. In D, there is a thickening of the filament and lamellae, with the reappearance of the interlamellar mass. Scale bars, 20 µm.