Fig. 2. (A–D) Chloride cells in the yolk-sac membrane of intact tilapia embryos (A,B) and yolk-ball preparations (C,D) incubated in fresh water (A,C) and sea water (B,D) for 48h. Chloride cells were detected by whole-mount immunocytochemistry with FITC-labelled anti-Na⁺/K⁺-ATPase. (E,F) Chloride cells in the yolk-sac membrane of yolk-ball preparations incubated in fresh water (E) and sea water (F) for 48h, double-stained with FITC-labelled anti-Na⁺/K⁺-ATPase and propidium iodide. Chloride cells in sea water form multicellular complexes with accessory cells (arrowheads), as demonstrated by the presence of more than one propidium-iodide-labelled nucleus. Scale bars: A–D, 50µm; E,F, 50µm.