Lumenized caudal fin sprout displays oscillatory blood flow. Time-lapse confocal imaging of Tg(kdrl:EGFP)s843; Tg(gata:dsRED)sd2 double transgenic embryos, where all ECs are labelled in green, and all erythrocytes are labelled in red in lateral views anterior to the left, 56hpf. Note oscillatory blood flow. Scale Bar: 20 μm.