Koi, like other fish, can survive for extended periods without eating. The actual period they can survive without food, however, is determined by several factors, including water temperature, the size and health of the fish, and their overall living conditions. Koi can usually live without food for about a week without any ill effects. However, if the water temperature falls below 50°F (10°C), their metabolism slows and they may be able to go longer periods without food, possibly up to two weeks.