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The following are excerpts from the Water Quality Seminar hosted by Olympic Koi Club on February 19, 2000 featuring Tony Prew (noted filter specialist) and Dick Benbow (noted water quality expert.) The article is written from notes recorded at the seminar by Tim Putaansuu who is more knowledgeable in web site design and fluid systems than water quality and filtration, so no guarantees of accuracy of this information are given.
As the temperature falls past 60°F towards 52°F, start cutting back the feeding to once every 3 days with a wheat germ food with no animal products. This caters to the slower digestion rates seen at these lower temperatures. When the temperature falls below 52°F, it is time to stop feeding altogether and let the fish go dormant. The fish cannot digest food below 52°F and the food rather rots in their system.
It is desired that the water temperature fall to less than 45°F at depth but not below 41°F due to concerns of frostbite and infection. Temperature at depth is usually figured by taking the temperature at the surface and adding 1°F for every foot of depth. The time spent between 52°F and 45°F should be minimized. The Koi's immune system is essentially shut down at these temperatures while parasites are still very active therefore giving the parasites an unfair advantage. Below 45°F, the parasites are no longer active.
Maintain flow and filtration 24 hours a day throughout the winter. The fish still need the clean water and oxygenation. Although most of us would wish for heated ponds to keep our fish active throughout the year, dormancy is sometimes a necessary cycle, especially for females greater than 3 years of age. The cold, dormant period forces the females to re-absorb the eggs she has that were not used in spawning. Otherwise the eggs will harden in place. Successive seasons with these hardened eggs building up would certainly lead to health complications and necessitate surgery to remove the petrified eggs. Besides helping to avoid this problem with females, the dormancy period is good for all fish in helping to set their color pigments.
Be careful with feeding too early. If the temperature drops below 52°F while the Koi have food in their system, they will not be able to digest the food and it will rot in their stomachs.
As the temperature rises to 55°F the fish's immune system starts coming online at about 25% effectiveness. At 60°F, 60% effective. At 70°F, fully effective. At 55-60°F, food with some white fishmeal may be introduced. Dick says a favorite staple for this temperature range is pearl barley cooked for 3 hours with a touch of garlic.
Springtime is another good time to catch your fish and examine them for any problems developed during their dormancy or from the warm up and treat them accordingly. Take this spring time examination as an opportunity to measure, photograph, and take records of your fish. Clean out any organic debris that has collected in the pond over the winter and clean out your filter system.
A warmer summer season allows for more active fish and higher growth rates leading to larger fish. However, considering the expense and the advantages of dormancy mentioned above, most of us will not elect to heat our ponds year round. Some advantage could be seen in installing a heater but using it mainly to help define the transition from activity to dormancy and back again. This helps prevent the false spring problem of having the temperature rise above 52°F where you start to feed the fish only to have the temperature fall back below 52°F and risk having all that food rot in their stomach. One can instead dust off the heater and turn it on for the next week or so to keep the temperature above 52°F and maybe even to 55°F where the immune system is more effective.
In fall, one can forestall the drop below 52° until the weather is cool enough that you know that the pond will smoothly sale through to 45°F to minimize the time spent in the parasite friendly zone. Manipulation of your pond's temperature should be undertaken with care. Rapid temperature changes are stressful to fish and may be fatal if the change is great enough.
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