Fig. 7. Electron-microscopic immunocytochemistry of gill chloride cells in tilapia adapted to freshwater (FW; A,B) and seawater (SW; C,D), incubated with anti-tilapia AQP3 (A,C) and with pre-immune serum as controls (B,D). Intense immunoreaction for AQP3 is observed along the membrane of the tubular system (arrowheads) continuous with the basolateral membrane in chloride cells of FW- and SW-adapted tilapia (A,C), but not in controls (B,D). m, mitochondrion. Bar, 200 nm.