Lying in the curvature between the stomach and the intestine is the spleen , which helps to removes waste products from the blood. The gills lie on either side of the pharynx and are thin-walled filaments which contain many tiny blood vessels. As the water moves over the filaments in the opposite direction of the blood flow, oxygen moves in and carbon dioxide moves out. Fish have many gill filaments that look like 'feathery' structures which can be seen when the operculum is pulled back, exposing the branchial chamber . The respiratory system works in conjunction with the circulatory system.
Blood is enclosed in vessels throughout the body and carries oxygen to the body tissues.
The fish has a two-chambered heart consisting of one auricle and one ventricle and is located beneath the pharynx. The heart pumps the blood to the gills, where carbon dioxide from the tissues is diffused outward and oxygen is taken in. The blood then travels to the body tissues where oxygen is taken in by the cells and used in several chemical reactions. The blood is under low pressure since the it travels through a single circuit, and not a double circuit as found in reptiles, birds and mammals. Excretory System Fish remove wastes from their body via the kidneys which are located above the stomach, just beneath the backbone.