Dissolved oxygen levels vary with temperature. Beware ...

Dissolved oxygen concentration

Q: At various times this summer I have seen my Koi gasping at the pond surface and around my waterfall.

A: Thanks for your letter which details your koi-watching observations, and provides your own helpful suggestions as to the cause of your gasping koi.

• Understandably, you may be surprised by an apparent DO (dissolved oxygen) deficit as you are already adding supplementary oxygen via aeration and a waterfall.
• Before being able to confirm whether your pond is sufficiently aerated during hot weather, it is first worth considering other factors that could lead to similar gasping behaviour in your koi.
• Nitrite: Besides a drop in DO (which is the most likely cause of the gasping behaviour you have observed) another cause could be that your koi are suffering from poor water quality, specifically nitrite toxicity.
• If for some reason, toxic nitrite is not being broken down and detoxified effectively by your biofilter, then it will cause a build up of nitrite in your pond water and then subsequently within your koi's blood and tissues.
• When nitrite reacts with the oxygen-carrying haemoglobin within the blood, it forms a stable non-oxygen carrying form of haemoglobin, which will in turn cause your koi to gasp.
• For this reason, the next time you observe your koi gasping (I hope you don't once you've read this reply), it would be prudent to carry out a water test to eliminate nitrite as the cause.
• The DO requirements of other organisms in your pond such as bacteria and other organisms will also increase.

pond oxygen-carrying koi water organisms aeration nitrite gasping weather medication "air pump" plants health reason "high temperatures" click for full article