Anatomy of finfish and shellfish

Unit 5 - Circulatory System

5.2.1.Blood Circulatory System
Cyclostomata
The largest number of seven to fourteen branchial arteries occurs in the lamprey – hag fishe group (cyclostomata) and depend on the number of gill pouches to be supplied. The branchial artery leads into gill filaments where it breaks up into capillaries in the lamellae, the capillaries reform into efferent vessels. In lamprey and hag fish the efferent branchial vessels rise dorsally one by one to join the mediam aorta. The first efferent branchial artery largely provides the blood supply for brain and head regions, although some arterial vessels principally the hyoid artery arise from the first afferent gill vessels.
The Dorsal aorta is the main route of blood transport from the gills to the body it is unpaired behind the gills to the trunk region, it runs behind the notochord.
The numerous branchial vessels that arise from he aorta and the corresponding veins are arranged/more or less to match the body segments. Lamprey and hag fish uniquely have valves to prevent back flow of blood to dorsal aorta.
The venous systems in cyclostomes have elaborate sinuses the systems in the hag fishes also have secondary heart in the form of contractile bulbs along the way as in the veins of the tail.
In lamprey posterior part of the digestive tract is supplied by vessel which have an artery placed in the lumen of a vein the blood from the intestine returns to the heart via the cardinal veins through suprearenal venous sinus.