Fig. 5. The influence of feeding on (A) the osmolality and (B) the urea concentration of the fluid phases of the gastrointestinal contents in stomach-1 (cardiac stomach), stomach-2 (pyloric stomach) and intestine in the dogfish shark. Simultaneously measured values in the blood plasma are also shown. Means ± 1 s.e.m. (N=6–8 at each time point). As points of reference, the dark bars represent the measured values for ambient seawater (SW) (N=4), and the light bars represent the estimated value for the ingested food [N=5; value for osmolality from Holmes and Donaldson (Holmes and Donaldson, 1969)]. Significant differences are not marked in A so as to avoid clutter; the only significant differences (P<0.05) within compartments are in plasma osmolality, as indicated by means not sharing the same letter in the following series: a=6 h, 30 h, 360 h; b=20 h, 120 h, 360 h; c=20 h, 60 h, 120 h. In B, within a compartment, means not sharing the same letter are significantly different (P<0.05). For clarity, x,y refers to stomach-2 and a,b to stomach-1.