The circulatory system of bone fish of any kind, as well as cartilaginous fish, has a single structure. In their body there is only one circle of blood circulation. Schematically, the divisions of the circulatory system of fish represent the following chain of successive components: heart, abdominal aorta, arteries on the gills, dorsal aorta, arteries, capillaries and veins.
The heart of fish has only two chambers and is not adapted, like other creatures, to perform the function of separating the flow of blood enriched in oxygen from blood not enriched in oxygen. Structurally, the heart consists of four chambers located one after another. All these chambers are filled with special venous blood, and each of the departments of the heart has its own name - venous sinus, arterial cone, atrium and ventricle. The departments of the heart are separated from each other by a valve, as a result of which the blood during contraction of the heart muscles can move only in one direction - in the direction from the venous sinus to the arterial cone. The circulatory system of fish is designed in such a way that the blood flow is carried out exclusively in this direction and nothing else.
The role of channels for the distribution of nutrients and oxygen throughout the body of the fish is performed by arteries and veins. Arteries perform the function of transporting blood from the heart, and veins to the heart. The artery contains oxygenated (oxygenated) blood, and the veins contain less oxygenated (deoxygenated) blood.
Venous blood enters the special venous sinus, after which it is electrocuted to the atrium, ventricle, and abdominal aorta. The abdominal aorta is connected to the gills through four pairs of efferent arteries. These arteries break up into many capillaries in the region of gill lobes. It is in the gill capillaries that the gas exchange process takes place, after which these capillaries merge into the efferent gill arteries. The carrying arteries are part of the spinal aorta.
Closer to the head, branches of the dorsal aorta pass into the carotid arteries. The circulatory system of fish involves the separation of each carotid artery into two channels - internal and external. The internal carotid artery is responsible for supplying blood to the brain, and the external one performs the function of blood supply to the visceral part of the skull.
Closer to the back of the body of the fish, the roots of the aorta merge into a single dorsal aorta. Unpaired and paired arteries branch sequentially from it, and the circulatory system of fish in this part supplies blood to the somatic department of the body and important internal organs. The spinal aorta ends with the caudal artery. All arteries branch into many capillaries, in which the process of changing the composition of the blood occurs. In the capillaries, the blood turns into venous.
Blood purification and its further current is carried out according to the following scheme. In the head area, blood is concentrated in the anterior cardinal veins, and in the lower part of the head it collects in the jugular veins. Passing from head to tail, a vein in the back is divided into two parts - the left and right renal portal veins. Further, the left portal vein branches, forming a system of capillaries, which form the portal system of the kidney located on the left. In most bony species, the circulatory system of fish is arranged so that the right portal system of the kidney, as a rule, is reduced.
From the kidneys, the circulatory system of fish drives blood into the cavity of the posterior cardinal veins. The front, back, and cardinal veins on each side of the body merge into the so-called Cuvier ducts. The Cuvier ducts on each side connect to the venous sinus. As a result, blood moved by current from internal organs enters the portal vein of the liver. In the region of the liver, the portal system branches into many capillaries. After this, the capillaries merge again and form the hepatic vein, which is connected to the venous sinus.