The system through which blood circulates in the body is called circulatory system. The blood circulation of cotton fish is closed. It shows unicyclic or unicyclic blood circulation. Circulation in which O2-rich or CO2-rich blood circulates through the heart in one cycle is called unicyclic or unicyclic circulation. The circulatory system of roe fish consists of four parts. Heart, Arterial System, Venous System and Blood. Dr. Siddiq Publications