Fish have a closed circulatory system which means the blood flows around the body in tubes, unlike insects who have an open circulatory system where blood flows freely in the body to bathe the tissues. They also have a single circulatory system, whereas humans have a double one. A single system means that blood is pumped to the gills to get oxygen and then to the rest of the body. On the other hand a double system pumps blood to the lungs, then back to the heart after which it pumped to the rest of the body.
