Figure 2: A: Section of O.niloticus gills of control group showing normal filaments and lining epithelium, H&E (Bar=100 μm). B: Section of O.niloticus gills of second group showing focal necrosis and sloughing in the covering epithelium of the secondary lamellae with intense lymphocytes infiltrations (arrows), H&E (Bar=100 μm). C: Section of O.niloticus gills of second group showing epithelial proliferations and fused at the base of gill filaments (arrows) besides severe congestion of the lamellar blood capillaries (arrowheads), H&E (Bar=100 μm). D: Section of O.niloticus gills racker of second group showing mucinous degeneration in the lining epithelium (arrow) and edema and EGCs infiltration in the submucosa (arrowhead), H&E (Bar=100 μm). E: Section of O.niloticus gills of third group showing hyperplasia of the covering epithelium in the interlamellar spaces, followed by fusion of the lamellae (arrow), congestion (arrowheads) and hemorrhages (irregular arrow), H&E (Bar=100 μm). F: Section of O.niloticus gills of third group showing severe congestion and focal hemorrhages (arrowhead) besides the hyperplasia in the lining epithelium (arrow), H&E (Bar=100 μm). G: Section of O.niloticus gills of fourth group showing mild hyperplasia in the epithelium of the secondary lamellae and congestion (arrow), H&E (Bar=100 μm).