This time of the year, as the ambient temperature drops for
winter, and the water in our koi pond gets colder, we are once again
made aware of the effect of temperature on our fish.
Our koi are cold-blooded creatures and their bodies function
at the temperature of the surrounding water. In fact, temperature has a
most profound effect on almost all the life forms in the pond. The fish
and plant life, micro organisms and even the bacteria in the biofilter.
It affects the rate of chemical activity within their body cells.
Consequently, as the water temperature drops koi will tend to eat less,
be less active, breathe slower and consume less oxygen. Food will move
slower through their gut as their metabolic processes slows down. At 11oC
it can take five days for food to move through their intestines. At
around 10oC the immune system of the koi effectively becomes
inhibited. The biofilter will also be ineffective and the bacteria in a
state of rest.
Because seasonal variations in weather may vary greatly from
place to place, koi keepers should be guided by the actual water
temperature and behaviour of their koi. Do not follow the prescriptions
of text books blindly.
As the temperature drops algal growth will slow down and the
pond water will become crystal clear. Oddly, the colours of the koi will
intensify and become brighter in cold water. Feed the fish an easily
digestible food such as wheat germ pellets. Do not feed too much. Below
12oC circulate the water less vigorously. If possible only
the top water in deep ponds should be circulated, leaving the bottom
water still and warmer. Water falls and venturi's will cause the water
temperature to drop more rapidly during cold spells. Flush bottom drains
Below 10oC koi go into a state of virtual
hibernation and will gather motionless in the deepest parts of the pond.
They should not be disturbed or offered any food, even when begging.
Written for Animal Talk magazine --
© Servaas de Kock & Ronnie Watt