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In our wonderful hobby of Koi Keeping we tend to fall into a deadly trap - overstocking our Koi ponds. Chris Neaves explains the effects stocking densities have on the water quality of our koi ponds.
Chris On Koi
Fishy stories, facts and myths as told at the edge of the koi pond by Chris Neaves.
Koi Pond Stocking Densities
In our wonderful hobby - koi keeping - we all tend to fall into a deadly trap, the trap of over stocking our ponds. Koi keepers often keep every koi they buy for as long as possible. Often the quality deteriorates but we still keep them and they keep on growing.
One of the fundamental principles of good koi keeping is good water quality. Look after the water and the water will look after your koi. As we add koi so the pond environment deteriorates as koi are continually feeding and growing. This in turn means that the oxygen is continually extracted from the water and toxic ammonia is added. Consequently the number of koi that can be safely kept in a koi pond (given volume of water) is limited.
It is very important to keep this in mind - each koi needs a minimum amount of water to live a healthy life and grow to its full potential.
Water has a limited koi carrying capacity. The oxygen that is dissolved into pond water being one of the main considerations for life is limited. Further as koi excrete toxic ammonia directly into the water there are limits as to the amount of ammonia koi can tolerate in a given volume of water - even with filtration.
Then from an aesthetic point of view it is far better to have fewer high quality koi than many poor quality koi. Try it one day - if you are over stocked remove the poor quality koi or the koi which are the poorest quality in your pond and then have a good look at your collection again. Suddenly the better quality koi will look better!
Lets us look in detail as to why are stocking densities are so important in koi keeping?
Quick Info
- Stocking densities have a direct influence on the overall health of your Koi and the quality of the pond environment.
- Heavily stocked ponds have a higher chance of disease out breaks.
- Heavily stocked ponds are stressful to Koi.
- The higher the stocking densities the faster you have to remove the impurities and the faster the clean water should be returned to the pond.
- As Koi grow they take up much more space, consume much more oxygen and add much more ammonia into the system.
Facts You Must Know
Every time a Koi doubles in length it has about 8 times more body mass. Than when the fish was half the size
This has severe implications on your pond and filter system.
8 times the body mass = 8 times more oxygen consumed + 8 times more ammonia added to the pond.
Higher stocking densities run a greater risk of the collection suffocating in the event of the pump being of for some time.
The graph of the estimated mass of koi as they grow illustrates the influence grow and stocking densities have on a koi pond. We have the same pump and the same filtration system but the koi are increasing in numbers as we add more koi AND they are influencing the pond water quality because of their increasing size.
- weight increases disproportionably with body length.
- a doubling in body length does not produce a doubling in mass -
- note the 7 - 8 fold mass increase as the length doubles from 20cm to 40cm
- each Koi can double in length in about two years, this would mean a 7 - 8 fold increase in the load on the biofilter and the oxygen demand - plan ahead
Decision Time
After a year or two, if your Koi have doubled, in length it may be decision time -
The effects of growth and body mass are illustrated below.
The Effects of Koi Growth on the Pond System.
Would you have originally stocked your pond with 640 x 10 cm Koi?
So the pond has suddenly become over stocked when the koi have grown and this is without any new additions.
There are other implications with stocking densities. Have you ever wondered why growing on dams and some ponds get very good growth? It's to do with low stocking densities and water quality.
Many Koi enthusiasts have great success with growing koi to a large size in relatively small ponds. Regular water changes are inevitably linked to good growth as as high turn over rates, large biofilters and reugular feeding of a good quality koi feed. Naturally temperatures have a direct bearing on growth.
An experiment by Andy Moo
A number of years ago Andy Moo wrote in Koi USA that he achieved 23cm of growth in his koi in 6 months. What was fascinating in his article is that he stumbled upon the growth by accident. Initially, Andy kept seventeen 10 - 13cm koi in a 1500 litre show tank. He noticed that the fish always appeared hungry so he gave them a light feed every time he walked past. Much to his surprise these fish grew from their original size to 25 - 33cm in less than five months.
Excited about his "discovery" he followed the initial results with several other tests. He chose 45 x 10 - 13cm "leftover" koi from his opening sale. These koi were placed in to his lily pond that is only 30cm - 60cm deep and has 5000 litres of water. Central to his experiments was the fact that he fed a good quality food and at estimated 2% body weight per day. This was increased up to 4% body weight per day as the temperature increased in summer. He increased the frequency of the feedings from four times a day up to twelve feeds per day.
Also central to the experiment was a high water turnover rate plus a large and efficient filter. At the end of just 166 days the average length of the 45 koi was 36cm. These tests were done in what we would consider a limited pond size and shallow depth. Andy observed that overall body conformation was excellent with none having potbellies, and with a few exceptions their colours did not fade but had actually improved.
If Andy can achieve growth like this in a relatively small pond, so can the rest of us.