Fig. 4. Typical changes in red blood cell perfusion in zebrafish under chronic hypoxic (A,C) and normoxic (B,D) conditions. Red blood cells were counted per minute at every position of the tissue, and represented in colour according to the calibration bar on the right. d.p.f., days post fertilization; a, anastomosis; an, anus; b, brain; da, dorsal artery; dv, dorsal vein; e, eye; g, gut; h, heart; iv, intersegmental vessel; sb, swimbladder.