Fig. 3. Effect of hypotonic and hypertonic saline infusion (75 and 500 mmol l^–1 NaCl, respectively) on (A) plasma and (B) urine potassium concentration and (C) their ratio (Urine:Plasma) in freshwater (open symbols) and saline-acclimated (filled symbols) mallards Anas platyrhynchos (circles), canvasbacks Aythya valisineria (triangles) and Barrow's goldeneyes Bucephala islandica (squares). The period of 500 mmol l^–1 NaCl infusion was subdivided into two parts: the period prior to secretion (–) and the period of secretion (+). Values are means ± S.E.M. (N=4 ducks per treatment).