In addition to the main source of heat loss at the gills, there is a significant amount of heat lost to the lower temperature water through the body surface. The southern bluefin tuna, being considered a large fish, has a relatively low surface-area-to-volume ratio. This low surface-area-to-volume ratio explains why there is a more significant amount of heat lost at the site of the gills compared to the body surface. As a result, the rete vascular system is located mostly at the site of the gills, but also at several other organs in the tuna. Specifically, due to the high metabolic demand of the southern bluefin tuna, the stomach is an organ requiring a high demand of thermoregulation. It is only able to digest food at specific temperatures, often much higher than the temperature of the surrounding water. Since the food is ingested along with a large amount of seawater, the contents must be heated to a temperature that allows the food to be digested and the nutrients and ions taken up. The southern bluefin tuna seems to increase blood flow to the stomach at times of increased digestion, by increasing the diameter of blood vessels flowing to the stomach, allowing more warm blood to reach the organ at a quicker rate.