Depth & Koi Growth
- the original essay
Posted on NI
Hi to every one,
This essay could not be posted as a single one. Too large I see. Please
read part 1 and part 2 together, as part 2 is a direct follow-on.
I was looking over the posts on pond depth below - my goodness but JR
is brilliant at stirring the pot!
Here is the original, un-censored article I wrote on pond depth a few
years ago for the South African Koi Keepers Society News Letter.
This essay was written in response to enquiries that were received after
publication of the article recalling my personal experiences on koi nutrition
in KOISA # 75. Society
members queried the statements that were made on depth and growth. Thank
you for the interest and response. In particular, members asked about
the statement - "It may come as a surprise to some collectors, but
I have never considered depth to be critical in achieving growth."
KOISA readers have asked me to elaborate on this statement. One
of the claims made in koi literature and by some South Africans are that
ponds have to be deep to achieve good growth in koi. Further claims were
and are regularly still made that koi keepers cannot grow koi to a large
size in a shallow pond. Please note the two words that have been highlighted.
The first two questions
I began asking myself, as I made notes of my observations over the years,
1. do all koi grow to a large size in deep ponds? and 2. do all koi remain
small in shallow ponds? The answer to both questions is clearly no. If
the answer to both questions were yes, this essay would end here. We could
then fall into line with so-called world opinion and live happily ever
after. The next two questions I started to ask myself were (no, I do not
always talk to myself, but thanks for asking) 3. how many large koi are
there in South Africa and 4. how many deep ponds compared to shallow ponds
No matter what we
are told or have been led to believe, it is an indisputable fact that
many koi keepers are growing koi to a large size in shallow ponds. When
I observed this fact I tried to find the other factors that must be present
that have a far greater influence on growth than pond depth.
The final straw that broke the camels back and turned me away from common
consensus was that koi are not easy to view in deep ponds. It is of concern
to me that people can pay a fortune for a fish and hardly ever see it
or at the very least see it with difficulty. Rather like an eccentric
art collector hiding beautiful works of art in a dark cellar never to
be seen again.
Koi are bred specifically
to be admired and appreciated. Year's ago I decided I would rather have
koi that were 60cm or 70cm (23 – 27 inches) long in a "shallow"
pond and see them each and every time I walked past, than a deep pond
with possibly slightly larger koi that were hardly ever seen.
Everyone has a different perception of what a "large" koi is
and what a "deep" pond is. We should therefore, define these
two concepts before engaging in debate.
Although we are told
koi can grow to a meter in length there very few koi of this size or even
90cm (35 inches) in South Africa (and the world?). The occasional 80 cm
(32 inches) koi is found. There are a very few genuine 70 cm or longer
koi, especially of high quality.
When we reach the 60cm - 65cm size bracket we find that most koi keepers
would be happy with koi of this length. We also discover that no matter
what we do and irrespective of pond specifications, the vast majority
of koi simply cannot grow much bigger than this size. Genetics becomes
the great leveller of the playing fields and the ultimate limiting factor.
Pond depth also needs
to be defined. A pond 1 meter deep (3ft) is considered shallow by many
enthusiasts. A pond 2 meters deep (6ft 5 inches) is considered deep. A
pond 3 meters deep (10 feet) is considered a tourist attraction. Ponds
below 50cm should not have koi in them. I agree, however, there are many
koi keepers who have ponds and water features that are 50-80cm deep that
have koi living quite happily in them.
We can confidently define a deep pond as a pond that is 2 meters or deeper.
Shallow ponds are defined as 80cm - 1.2 meters in depth. Anything in between
is a medium depth pond.
One finds that statements
on pond depth originate from the UK and from Japan. The main reason for
deep ponds in these countries is their extremely cold and more importantly
- long winters. In parts of Japan and the UK pond water temperatures frequently
drop below 5*C in the long winter months. Some ponds freeze over. Not
only this, they remain very cold for much longer periods than in South
Africa. It is the length of time that ponds remain cold that is problematic
What is a problem
with temperature, and this has been widely published in the UK, is the
length of winters. In order to bring some relief to koi in long, cold
winters, deep ponds are made. At 4*C a peculiar thing happens to water,
an inversion takes place. The "colder" water rises and the "warmer"
water sinks. This is why ice floats. The middle water is then drawn to
keep the lower levels stable and undisturbed. The koi can settle in the
lower regions and wait out the winter months in a state of semi-hibernation.
In South Africa we
do not experience water temperatures as low or for as long as in the UK
and Japan. As a matter of fact many overseas visitors have made the comment
that South Africa has ideal conditions for growing koi - long hot summers
and short mild winters in most parts of the country.
The other information
regarding depth and growth is split into camps of different opinions.
One claims that the vertical swimming provided by depth is very important
for growth and body shape. Another camp claims that it is the increased
water pressure of deep ponds that influences body shape during growth.
And another opinion is that the air bladder needs depth - i.e. pressure.
There is one further theory I have come across about depth - koi need
depth because they have to stand on their tails to feed. The exponents
of this latter theory claim that because koi cannot stand on their tails
in shallow ponds they cannot feed properly and consequently do not grow
Depth will affect
body shape to a certain degree, as the muscles exercise against the pressure.
Depth will possibly strengthen the air bladder but can someone please
explain the theory of vertical swimming having an influence on body shape
and growth? Exactly how does swimming vertically improve body shape? Even
in the east there does not seem to be consensus on depth amongst enthusiasts
as Takayuki Izeki made a statement in Nichirin - " if water is deeper
(2 meters) the water pressure hinders growth and a good body shape cannot
be hoped for."
Another factor not mentioned with regard to pond depth is that, in some
countries, it is much cheaper to dig down an extra meter to increase water
capacity than it is to extend the surface area for the same purpose.
Perhaps we should
reach common ground. Is water temperature essential for growth? Yes. We
know koi do not grow in low water temperature. It is easy to see that
there will be no growth in a deep pond with a water temperature of 5*C.
However, there will be growth in a shallow pond with water temperature
of 25*C. Common ground has been reached. Temperature is essential for
Is oxygen essential for growth? Yes. The examples in the above paragraph
apply here as well. I have come across an interesting claim that it is
very difficult to grow jumbo koi on the high veldt in South Africa (6,000
feet above sea level). If I recall correctly, this persons definition
of a jumbo koi was 75cm or bigger. It was maintained that we cannot get
enough oxygen into the water. About 20% less oxygen can be dissolved into
water on the high veldt than at the coast. Couple this with the high water
temperatures we get in our ponds and he could very well be right. (both
altitude and temperature affect oxygen levels in water).
Is water quality
essential for growth? Yes. If the water quality is poor your koi will
probably not be growing because they are dead. Jokes aside, water quality
is applicable in all circumstances.
Is food, or more specifically nutrition, essential for growth? Yes. A
group of koi in a deep pond that never receive any food will not grow.
Koi in a shallow pond that do receive food will grow.
Nutrition from birth
is possibly the most critical factor in achieving growth other than genetics.
Plus the closely interconnecting factors of oxygen, water quality and
temperature. I request readers to re-read some of the statements I made
in the article on koi nutrition. One of the most important was - people
are underfeeding their collections on quality food, which is one of the
main reasons why they do not get growth.
It is a fact that koi keepers are growing koi to 70 and 80cm, with very
reasonable body shapes, in "shallow" ponds of about one meter.
It is a fact that jumbo koi of above 70 - 75 cm are rare, both here and
in Japan. Yes, some society members have visited very wealthy koi keepers
in the east with ponds full of high quality jumbo koi, but relative to
the total numbers of koi in the world and relative to what we can afford
in South Africa, jumbo koi are rare. Recent personal discussions with
Takeda san produced the following reply to the question - how many good
quality jumbo koi are there in Japan? The reply - maybe a thousand.
This brings us to
the crux of the matter - my statement - I have never considered depth
to be critical in achieving growth (size). Depth may have a minor influence
on body shape of some koi. Depth may have a minor influence on the rate
of growth in some well-fed koi. But a deep pond cannot and will not guarantee
you size. In most cases depth can easily be compensated for by exercising
the koi against a current to achieve the ideal body shape. While it is
wonderful to have the best - i.e. a pond of 2 or 3 meters deep, is this
pond depth critical to the growth of the fish? The answer is no. There
are other factors that can be classified as critical to growth.
At some point we
must ask ourselves - do we want to attract people to the hobby with reason
and reality? Not everyone wants or can afford a tourist attraction. Not
everyone wants a pond with hundreds of thousands of litres of water. We
therefore, have to weigh up the pros and cons of recommendations on pond
specifications from a practical point of view that will accommodate the
wishes, needs and budgets of the vast majority of koi keepers.
Kind Regards, Chris