Fig. 3. (A) Haematocrit (%), (B) plasma osmolality (mOsm kg^–1) and (C) plasma angiotensin concentrations (pmol l^–1) of river lampreys acclimated to freshwater at 15 mOsm kg^–1. Control lampreys (non-injected; black bars) were held under light anaesthesia for 15 min (N=8) and 30 min (N=4) in the absence of further manipulation. Experimental lampreys were blood sampled at either 15 min or 30 min after an i.p. injection of 1% body mass with either isosmotic saline (white bars; 120 mmol l^–1 NaCl; 233 mOsm kg^–1; N=5 at each time point) or hyperosmotic saline (cross-hatched bars; 4 mol l^–1 NaCl; N=5 at 30 min; N=8 at 30 min). Different letters above error bars signify groups that differ significantly (ANOVA and post-hoc multiple comparison tests).