Fig. 1. Anatomy of the zebrafish trunk and its blood vessels at 3 days post-fertilization. At this stage, there is active flow through the dorsal aorta, (DA), posterior cardinal vein (PCV) and most intersegmental arteries (ISA) and intersegmental veins (ISV). The ISA and ISV are linked together dorsally via paired dorsal longitudinal anastomotic vessels (DLAV). All of these vessels are shown relative to adjacent tissues and structures in the mid-trunk including the gut (G), myotomes (M), notochord (N), neural tube (NT), left pronephric duct (P) and yolk mass (Y). In addition to the functioning vessels noted above, parachordal vessels (PAV) run longitudinally to either side of the notochord, along the horizontal myoseptum. The parachordal vessels are linked to the posterior cardinal vein and intersegmental veins (arrows), but generally not to intersegmental arteries. At 3 dpf, the parachordal vessels do not yet carry flow. Anterior is towards the left and above the plane of the page, and dorsal is upwards.