Like that of the cartilaginous fishes, blood vascular system consists of a “single circulation.”
It consists of the fluid part, plasma and blood corpuscles. Erythrocytes are elliptical and nucleated with haemoglobin. Besides erythrocytes, nucleated reticulocytes and thrombocytes, as well as coarse and fine granulocytes and various lymphocytes occur. Haematopoiesis occurs chiefly in teleosts in the kidney intertubular tissue and in the spleen.
Heart is placed in the pericardial coelom ventral to the oesophagus and enclosed within thin-walled pericardium. Heart is 2- chambered, consisting of sinus venosus, atrium and ventricle. Sinus venosus is a thin-walled sac placed dorsally over the atrium and ventricle. It receives deoxygenated blood from the entire body by right and left ductus Cuvieri. Auricle lies ventral to the sinus venosus and is a thin-walled single chamber. It receives blood from the sinus through a valved sinu-auricular aperture.
The auricle opens into a thick-walled ventricle by atrio-ventricular aperture guarded by valves. These valves prevent the flow of blood in reverse direction. There is no conus arteriosus.
The proximal end of the ventral aorta is dilated to form a thin-walled elastic bulbus arteriosus. It differs from a conus in being part of the aorta, and not the heart. The bulbus arteriosus in teleosts dilates and contracts as a response to the beat of the ventricle, and by this means pressure through the short aorta to the gills is maintained.
Like elasmobranchs the heart action is regulated by a depressor nerve of vagal origin. Sympathetic innervation is lacking. The heart is called the venous heart since only deoxygenated blood circulates through the various parts of the heart.
There are two types of arteries- afferent branchial arteries carrying the deoxygenated blood from the heart to the gills and the efferent branchial arteries carrying the oxygenated blood from the gills to the entire body.
(i) Afferent Branchial Arteries:
From the ventricle arises a stout ventral aorta whose proximal part is dilated to form the non-contractile bulbus arteriosus. The ventral aorta runs forward along the mid-line of the floor of the pharynx and close to the hyoid arch bifurcates into a first pair of afferent branchial arteries which goes to the first pair of gills. The second, third and fourth pairs of afferent branchial arteries originate independently behind the first pair and enter the second, third and fourth pairs of gills. All these four pairs of afferent branchials carry deoxygenated blood to the gills.
(ii) Efferent Branchial Arteries:
They carry oxygenated blood to the different parts of the body and not to the heart. Like afferent branchial arteries, efferent branchial arteries are also four pairs. The first and second efferent branchials on either side unite to form the anterior epibranchial artery. Both the anterior epibranchial arteries unite posteriorly along the mid-dorsal line to form the dorsal aorta. The third and fourth efferent branchial arteries on either side unite to form the posterior epibranchial artery.
These two communicate with the anterior end of the dorsal aorta. The first efferent branchial artery on either side gives off a cephalic artery which further divides into an external carotid artery that supplies blood to the orbital region, tongue and hyoid arch, and an internal carotid artery goes to the brain. The dorsal aorta runs backwards along the ventral side of the vertebral column and enters the tail as caudal artery.
Along its route, dorsal aorta gives the following arteries:
(a) A coeliaco-mesenteric artery for swim-bladder, stomach, intestine, liver, spleen, etc.
(b) A pair of subclavian arteries, each dividing into a pectoral and a pelvic arteries for pectoral and pelvic fins.
(c) A number of paired segmental arteries for segmental muscles.
(d) A few pairs of renal arteries to the kidneys.
(e) A pair of genital arteries to the gonads.
Veins of the venous system carry deoxygenated blood to the sinus venosus. The blood is carried to the sinus venosus by right and left ductus Cuvieri. Each Cuverian duct is formed by three veins, anterior cardinal sinus, a jugular sinus and a posterior cardinal sinus. The posterior cardinal sinus receive segmental veins, renal veins and genital veins, etc. Ductus Cuvieri also receive pectoral and pelvic veins, and a hepatic vein.
The caudal vein from the tail after entering into the trunk region bifurcates into two branches- right posterior cardinal sinus passes through the substance of right kidney and opens into the right ductus Cuvieri. The left posterior cardinal sinus arises from the capillaries of renal portal veins.
A vein that originates from capillaries and ends up again into capillaries in other organ before going to the heart is called portal vein and the system is called portal system.
There are two Portal Systems:
(i) Renal portal system and
(ii) Hepatic portal system.
(i) Renal Portal System:
The left branch of the caudal vein enters into the left kidney and breaks up into capillaries and forms the renal portal system. These capillaries rejoin forming the left posterior cardinal sinus.
(ii) Hepatic Portal System:
The veins from the various parts of the alimentary canal unite to form the hepatic portal vein. It enters into the liver and breaks up into capillaries and these capillaries reunite forming the hepatic vein that communicates with the ductus Cuvieri.