Features of the structure of the circulatory system of fish.

Fish are cold-blooded aquatic vertebrates that can be found in both salt and fresh water. Like humans, they have a closed circulatory system in which blood is always contained in a chain of blood vessels. In other words, the blood never leaves the blood vessels or fills the body cavities. A closed circulatory system can have one or two types of circulation. Fish have one pattern of circulation, in which blood passes through the heart only once during each complete circuit. Gaseous exchange takes place inside the gills and the oxidized blood from the gills circulates throughout the body.