Fig. 1. Variability of the Root effect in haemolysates of selected African fishes. The magnitude of the Root effect is measured as the difference in percentage Hb O₂ saturation between the two plateaus at high and low pH. Presence and absence of choroid and swimbladder retia mirabilia are indicated for each species. Hb O₂ saturation of functional Hb was determined using diluted, air-equilibrated samples (5–15 µmol l^–1 [Hb₄]) by spectral deconvolution between 500 and 700 nm (Völkel and Berenbrink, 2000). Measurements were performed at 25°C without removal of organic phosphates in 50 mmol l^–1 Tris HCl buffer (pH 8.0–6.5) and 50 mmol l^–1 citrate buffer (pH 7.0–5.0) in the presence of 0.1 mol l^–1 KCl (M. Berenbrink, unpublished). Fish line drawings modified after: Lehrbuch der Speziellen Zoologie. Begruendet von Alfred Kaestner. Band II: Wirbeltiere, 1991©Elsevier GmbH, Spektrum Akademischer Verlag, Heidelberg.