Hippocampus, exocetus and anabas belong to the family of fishes. Fishes have 2 chambered heart, one atrium and one ventricle. Blood is pumped to the gills by heart to be re-oxygenated, from where the blood flows to rest of the body parts and returns back to the heart in just one circulation. Fishes have low blood pressure in body capillaries due to single circulation.