Water Temperature koi sturgeon pond

Koi are a very hardy fish having the ability to survive in a wide temperature range of 2-30 degrees C ( 36-85 degrees F ). In their native Japan the winters are very cold however they are also relatively short.
In Northern Europe and Northern America conditions can become extreme and are often a very long season of winter conditions. It is then under the extreme conditions that most problems may become present.
Temperature in winter is more easily controlled than in the summer, by use of a water heater. Many koi keepers run their heaters to maintain a water temperature of around 6-10 degrees C during the winter. This water temperature will remain constant should the ambient temperature be fluctuating widely. Every country can have warm days in the winter, ambient temperatures will rise during the day and considerably drop at night, with a heater in place the water will be maintained at a steady set temperature.
Sturgeon have a lower temperature threshold, they will feed in the lowest temperatures and the most common problem with sturgeon come in the summer months when temperatures are high and oxygen levels are low. A water temperature of 24-26 degrees C is at the top of a sturgeons limits, If temperatures rise above this and remain above for a period of time a 10 - 15% water change should be made using a fine mist hose spray to top the pond level back up. This chills the water slowly, adds important oxygen and will also defuse the chlorine from tap water as it hits the air. An air pump in a pond with sturgeon is vital, you should be aiming for an oxygen content of 6mg per litre minimum.