Most of the animals that live on earth need sunlight in some way, either indirectly or directly. Koi need sunlight in both ways. Be it in the plants they eat or for their color pigments that they produce. Natural sunlight brightens a Koi’s colors. This is most evident with the Yamabuki Ogon. If a Yamabuki Ogon is kept in an indoor tank with only regular lighting, its yellow color will fade. But, if the Yamabuki Ogon is put in an outdoor pond, its color will return within a couple months. The same applies for Kohakus, Sankes, Showas ect. Koi actually look better in natural sunlight too. There’s something about the broad spectrum of light that the sun produces that brings out the natural beauty of Koi. A good way to see this example yourself is to take two pictures. Take one of a Koi when it’s indoors under a regular light and one of a Koi outside on a nice sunny day. Compare the two photos and it’s easy to tell which one looks better. Natural sunlight also makes Koi healthier. The sun will warm the water up and will also boost a Koi’s immune system. Humans get vitamin D from the sun, fish do not. They must get it from plants or the small organisms that they eat. Vitamin D is essential for good growth and strong bones. Natural sunlight is also beneficial to aquatic plants too. Aquatic plants require sunlight for photosynthesis, which is the process that a plant uses in order to make food and oxygen. The sun poses dangers to Koi too. A pond in direct sunlight can easily overheat in the summer. When the pond temperature goes up, oxygen levels go down. Don’t forget about UV radiation from to sun too. A pond should always have a shaded area. This will provide a place for the Koi to go to during the hottest and brightest parts of the day. The shade will also help keep the pond temperatures down too. Natural sunlight has a compounding beneficial affect on Koi. It gives them food, makes them healthier and it makes them more beautiful. Back to Koi Care.