Arterial and Venous System of Teleost

Teleost is a diverse group of ray-finned fishes which belongs to largest infraclass Teleostei under the class Actinopterygii. The group teleost includes 40 orders and 448 families with over 26000 species. They are the most advanced fish among the bony fishes. The world`s important sport and commercial fishes include this group. The length of the teleost ranges from 6.2 mm to 7.6 m or more. In this case, the giant oarfish (Regalecus glesne) grows up to 7.6 meter in length or more with over 1 tons in weight while the male angelfish (Photocorynus spiniceps) grows up to just 6.2 mm in length.

In the blood circulatory system, the arterial system is the higher-pressure portion. In this case, arteries carry oxygenated blood (exception the pulmonary artery) away from the heart. All the arteries contains a thick tunica media than veins.

Arterial System of Teleost

The ventral aorta moves forward and gives off four pairs of afferent branchial blood vessels of which third and fourth pairs originate from the same common location of the ventral aorta and supply blood to the third and fourth gills. These blood vessels travel to the holobranchs on each side and reach to the paired blood capillaries of the gill lamellae. In gills, blood is oxygenated and blood is collected through four pairs of efferent branchial arteries.

Each gill arch contains one efferent blood vessel, the first two of these originate dorsally from  the gills and connects to form the first epibranchial blood vessel. The epibranchial arteries on both sides runs the posteriorly and join to form the dorsal aorta. The third and fourth efferent branchial blood vessels originate from the corresponding holobranch and join to form a short second epibranchial blood vessel which opens into the dorsal aorta.

A short common carotid artery originates from the first efferent branchial blood vessel, protrudes and divides somewhat to form an external carotid and an internal carotid artery. The carotid artery near its base receives blood from an efferent pseudobranchial artery coming from the pseudobranch. A cerebral artery is generated from the common carotid artery and supplies blood to the brain. The external carotid artery divides into numerous branches and supplies blood to the operculum, auditory region, and muscles of the jaw.

The internal carotid artery supplies blood to the snout and optic region. A small branch is formed from the internal carotid artery and goes along the midline towards the front and joins with the branch coming from the other side to form the circulas cephalicus. The dorsal aorta extends posteriorly below the vertebral column. The subclavian artery arises from the dorsal aorta just behind the second epibranchial artery and supplies blood to the pectoral fins.

The coeliaco-mesenteric artery arises from the dorsal aorta just behind the subclavian artery and progresses a little further, splitting into two branches called the coeliac and mesenteric arteries. The coeliac artery supplies blood to the anterior region of the intestine. On the other hand,  mesenteric artery gives off branch and supplies blood to the liver, spleen,  gonads, and to the rest of the alimentary canal.

The dorsal aorta reaches through the kidney and produces a few pairs of renal arteries on its lateral side. One of these pairs reaches into the two pelvic fins, and then the dorsal aorta continues posteriorly, becoming known as the caudal artery along the middle of the haemal canal, and gives off a few pairs of segmental arteries that expand into the muscle during its course.

The above description represents an ideal arrangement of arterial system in teleost. However, some variations in the arteries can be observed in different species of freshwater, such as the four pairs of afferent branchial arteries arise in the Catla catla that originate independently. However, in Mystus aor, Rita rita, Tor tor, Clarias batrachus, Heteropneustes fossilis, Wallago attu, Chitala chitala, the third and fourth arteries on each side originate from the same common place. In a very small number of species of fish, such as Rita rita and Heteropneustes fossilis, the second pair of afferent arteries originate in the same common way from the ventral aorta.

In some species, such as the Catla catla, Tor tor have a pseudobranch which arise from first efferent branchial artery and receives blood supply through the afferent pseudobranchial artery. Blood is collected through the afferent pseudobranchial artery that connects to the internal carotid artery. Mystus aor does not have a pseudobranch. In this case, the base of the internal carotid artery is swollen to form a labyrinth.

The alimentary canal and its associated glands receive blood supply from the branches of the coeliaco-mesenteric artery. The gonads receive blood from the coeliaco-mesenteric or the posterior mesenteric arteries.

Venous System of Teleost

Blood is collected from the head through the external and internal jugular veins which combine on each side to form the anterior vein. The internal jugular veins receive blood supply from the premaxillary, nasal, and eye regions. External jugular veins, on the other hand, collect blood from the maxillary and mandibular regions.

The anterior cardinal vein receives blood from the opercular and subclavian veins before opens into the ductus cuvieri. A single inferior jugular vein collects blood from the ventral surface of the pharynx and is exposed to the sinus venosus.

There is a single posterior cardinal vein in the teleost that reaches to the right kidney. The renal veins coming from both kidneys are exposed to the posterior cardinal vein and runs forward and is exposed into the sinus venosus.

The blood coming from the tail is collected through the caudal veins which gain some segmental veins and are exposed to the kidneys. Hepatic portal veins collect blood from different regions of the alimentary canal, spleen, swimbladder, and gonads and reach to the liver. Later, two hepatic veins are generated from the liver and supply blood to the sinus venous.

In Tor tor, this venous system represents the ideal venous system of teleost. However, some variations in the venous system can be observed in different species of freshwater fish.

The inferior jugular veins are usually unpaired. But in some fish, such as Clarias batrachus, have two inferior jugular veins. In Tor tor, Catla catla, Wallago attu, the posterior cardinal veins are unpaired. However, in Clarias batrachus it is paired. Although the right posterior cardinal vein is more developed in this species.

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