Goldfish get their oxygen from water. As a fish swims, it gulps up water. The water which has oxygen goes through an opening in the fish’s throat that leads to the gills. Gills have many blood vessels within them. Oxygen moves from the water to the blood as the water flows over the gills. The blood vessels gather and store the oxygen that travels over the gills. At the same time, carbon dioxide moves out of the blood and into the water. Now, the water flows out of the slits beneath the gills. These gills are located under the operculum.