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.
Solid wastes leave the body through the anus.
Ripe eggs pass out of the ovaries into the general body cavity and can completely fill the space. The eggs leave the body through the urogenital opening. Female fishes lay hundreds, or even millions, of eggs. The male releases milt containing sperm, over the eggs. Only a few eggs hatch to become adults.