Most animals need natural light in order to thrive and koi certainly benefit from the sunshine. There are many ways in which sunlight will benefit your fish but it is important to strike a good balance of light and shade. There is much to think about when caring for your koi but their need for light should never be overlooked.
Natural light and colour in koi
Natural sunlight brightens the wonderful colours of koi. This is particularly true of the Yamabuki Ogon. If a Yamabuki Ogon is kept in an indoor tank, its gorgeous golden yellow colour will inevitably begin to fade. However, that gorgeous colour will return within two months of the fish being placed in an outdoor pond. The colour of all koi will be negatively impacted if they are not exposed to sufficient amounts of light.
Koi actually look better when viewed in natural sunlight. The broad spectrum of light that the sun produces brings out the natural beauty of the different varieties of the fish.
Natural light and koi health
Koi are more likely to thrive in a pond warmed by sunlight and boasting good plant growth. Koi need vitamin D just like people but do not get this directly from sunlight as we do. The fish gain the vitamin from the plants and organisms that they eat. Vitamin D is essential for good growth and general health in koi. Vitamin D also promotes plant growth and so is vital for a creating the right pond environment for the fish to thrive.
Day and night cycles
All animals have circadian rhythms and it is important that these are not disrupted. Circadian rhythms are controlled by the natural cycle of darkness and light. It is therefore crucial to ensure that your pond is positioned in such a way that it isn't too shady and will be exposed to natural light in the daytime. The fish need to sense the daily and seasonal changes which influence their metabolisms.
Too much of a good thing
While sunshine is generally a good thing, it can also pose a danger to your fish. Too much direct sunlight can cause your pond to overheat in the summer months and this will result in the oxygen levels in the water falling. UV radiation can present a danger to koi and so it is important that there is a shaded area for them to retreat to during the hottest and brightest periods of the day. A shaded area will also help to balance the water temperature in the summer.
You should also be aware that too much bright light over your pond can encourage excessive bacterial growth and spark algae blooms. You need to get the balance of light and shade just right to provide your fish with all of the benefits of the light and not the downsides.
It is possible to keep koi indoors but they are better suited to life outdoors where they have the space and the natural light that promotes good health.