Features of blood circulation and respiration in fish.

Fish have a closed circulatory system, and there is only one circle of blood circulation. The bicameral heart consists of one atrium and one ventricle. The heart contains venous blood. From the ventricles, blood enters the abdominal aorta and then into the branchial arteries. Gas exchange takes place in the capillaries of the branchial lobes. Arterial blood enters the spinal aorta and through the arterial system – to tissues and organs, where it releases oxygen through the walls of the capillaries. Venous blood flows through the cardinal veins into the atrium.
The respiratory system contains gills, which consist of gill arches, on which on one side there are gill petals, which are penetrated by blood capillaries, on the other side there are gill stamens (filter apparatus).
In cartilaginous fish, gill covers are absent, and water circulation is ensured by constant movements.
In bony fish, the gills are covered with gill covers, the movement of which, including the mouth cavity, creates a constant flow of water.