Q Do fishes present an closed or open circulatory system? How many chambers does a fish heart have? How does blood flow throughout the fish body?
As in every vertebrate the circulatory system of fishes is closed that is blood flows only within blood vessels.
The fish heart has only two consecutive chambers: a muscular ventricle and a thin-walled atrium. The arterial (oxygenated) blood comes from the gains and gills arteries towards tissues, and then venous blood is collected by veins and reaches the atrium of the heart passing to the ventricle that pumps the venous blood towards the gills to be again oxygenated.