An Interactive Atlas of Zebrafish Vascular Anatomy

3-3.5 Days Post-Fertilization
The trunk and tail SE are relatively unchanged at this stage, the basic pattern having been established by approximately 2.5 dpf, as noted above. The DLAVs in the caudal trunk and tail are just beginning to form a simpler single plexiform vessel. Two additional types of trunk vessels newly sprout at about this time, extending horizontally (along the A-P axis) from some of the SE in both directions (sprouts are apparent in [3.5 dpf overview], also see [trunk section] for positions of these vessels in a trunk cross section at 5 dpf). The more dorsal vessel is the primordial vertebral artery (VTA). A pair of VTA form on either side of the base of the spinal cord, adjacent to the myotome. The more ventral vessel is the parachordal vessel (PAV). A pair of PAV form lateral to the notochord, adjacent to the myotome, at the level of the horizontal myoseptum. Both sets of vessels begin to sprout in the trunk at approximately 3 dpf, and in the tail at approximately 3.5 dpf. Most of these sprouts remain very short and the majority do not begin to progress to span the somite until 4-5 dpf. D-V separation between the axial vessels (DA and PCV) continues to increase, and the CV plexus continues to slowly condense down into a single more ventral channel. Beginning at approximately 3.5 dpf, a profusion of short vessels appears in the trunk between the DA and PCV (see [4 dpf overview] and [4.5 dpf overview]). Most of the vessels are transient, and have largely disappeared by 4.5-5 dpf. The nature of these vessels is not at present understood, and awaits further (histologic) analysis.

The CCV continues to narrow and move to a more cranial path as it swaths across the yolk ball. The right PCV is by now almost completely dominant, with the left PCV draining SeV from only the first 1-4 segments [later 2.5 dpf head lateral]. The AMA and its branches in the ventral-cranial trunk are very difficult to visualize by fluorescent microangiography but more readily observed in Berlin-blue injected specimens [AMA & derivatives]. As already described briefly above, the AMA takes off ventrally from the DA just caudal to the pronephric glomus (P). Paired vascular loops for the glomus are visible draining into the AMA. Shortly after it exits the DA the AMA branches into the SBA and the SIA. The SBA runs directly caudally, then branches to form the simple plexus on the right and left sides of the swim bladder at 2.5 dpf. The left plexus drains into the left subintestinal vein from its cranial end, but we have not been able to identify this connection on the right side yet. By approximately 3 dpf the plexus has elongated across the full A-P length of the swim bladder, and has formed multiple loops by approximately 3.5 dpf. The SIA also continues caudally, forming numerous connections to the two SIV on either side of the gut wall [3.5 dpf overview]. The most cranial connections on the right side represent the vessels vascularizing the pancreatic anlage on the right intestinal wall [AMA & derivatives]. The SIVs run cranialwards along the yolk or the ventral walls of the intestine on both right and left sides where they still serve to absorb the yolk. They drain into the liver independently via separate primary hepatic portal veins (HPV). These embryonic HPV are different from the secondary hepatic portal vein that detours across the gut at the dorsal boundary between fore- and a mid-gut in adult vertebrates (see discussion).

The connections between the aortic arches and cranial arteries are detailed in [3.5 dpf arch-head]. Although the aortic arches are in a similar configuration to that found at 2.5 dpf, sprouts first begin to appear on the caudal four aortic arches (AA3-AA6) at approximately 3 dpf, usually on their caudal-lateral surfaces [3 dpf arches]. These sprouts will give rise to the branchial laminar arteries (ALB) of the future gills. By 3.5 dpf the third, forth and fifth aortic arches have started to divide into afferent (proximal to the ventral aorta) and efferent (proximal to the lateral dorsal aorta) branchial arteries (ABA and ABF, respectively). This process, which proceeds in a rostrocaudal direction from AA3 to 6, continues for the next several days (see [3.5 dpf arch-head] and [4 dpf arches]. At this stage there is still a direct connection between the end of the ABF and the ABA. By 3.5-4 dpf the vascular sprouts that first appeared at 3 dpf on the four caudal aortic arches are now starting to become short loops [3.5 dpf arch-head], [3 dpf arches], [4 dpf arches, ventral], and [4 dpf arches]. Eventually they will form loops with the two ends entirely disconnected, one end linked to an ABA and the other end linked to the corresponding ABF. At this stage of development, ALB sometimes still have a single "stem" proximally even if there is a loop at the distal end. The afferent (proximal to the ABA) portion of each loop is called the afferent laminar branchial artery (ALBA) and the efferent portion (proximal to the ABF) is called the efferent laminar branchial artery (ALBE). Another new vessel associated with the aortic arches also appears at this stage, the hypobranchial artery (HA). A pair of HA are initially present, one taking off from each AA1 [3.5 dpf arch-head], [3 dpf arches] and [4 dpf arches, ventral]. They run rostro-medially until at the extreme rostro-ventral midline the two vessels merge and then run straight caudally along the ventral midline until they reach the rostral end of the VA. There, the single HA passes just dorsal to the rostral end of the VA, and then immediately splits again into a pair of HA. The paired HA continue caudally just to either side of the ventral midline, passing dorsal to AA1, ORA and AA3, and then ventral to the more caudal arches AA4, AA5, and AA6. The HA provide blood supply to the ventral branchial region and the heart.

In the cranial vascular system, the connection between the caudal end of the PHBCs and the DLAVs becomes a connection primarily to the BA during the approximately 3-4.5 dpf time period [3.5 dpf head dorsal multiulayer composite]. The BA had been connected to the PHBCs at their caudalends by 1.5-2 dpf, so this circulatory route was already present. But with the PHS coming on line and becoming the primary route for venous drainage from the head, the caudal PHBCs now drain rostrally into the PCeVs, and a vascular feed for the head-DLAV vascular link must come entirely from the BA. These changes are displayed diagrammatically in [head-trunk connections]. Although many additional cerebral capillaries continue to form in the head through these stages, and exiting vessels may be significantly remodeled, the basic wiring plan of major vessels established by 2.5 dpf is still maintained at this and later stages.