Fig. 5. Immunohistochemical images of freshwater tilapia gill frozen sections. (A–C) Double labeling for glycogen synthase (GS) and Na⁺/K⁺-ATPase (NaK); (D–G) double labeling (arrows) for GS and glycogen phosphorylase (GP); (H–K) double labeling (arrows) for GS and glycogen. A, D and H are DIC images. GS, GP and glycogen were co-localized in a specific group of glycogen-rich cells (GRC) that are adjacent to mitochondrion-rich cells (MRC; labeled with Na⁺/K⁺-ATPase). White dots indicate the outline of the cells. Scale bar: 10 µm (A–C) and 20 µm (D–K).