Koi in mud ponds

I am about to start building my first ever koi pond but wanted to ask some advice first on which style to have.

My garden has a lot of clay in the soil and is very rich in minerals and nutrients (I’ve had it tested), so I am toying with the idea of building a natural mud pond Japanese style. Because this is my first pond I’m not sure how difficult this would be, so do you think it would be best to go for a standard lined pond.

I would need to know any benefits and downsides to having a natural pond against a man-made pond then this may help me make up my mind.

Hope you can help?

Thanks for the opportunity of giving you some advice on a topic that is very hotly debated amongst koi keepers. In fact, it is very refreshing to receive an inquiry from someone who is contemplating constructing a natural mud pond in their garden rather than the traditional highly filtered, recirculating, gin-clear koi pond. You are obviously very wisely thinking about your pending project from a koi’s perspective, motivated by what you think will be best for your koi, rather than yourself.

By even raising the possibility of digging either a natural or lined pond, you have already given it some serious thought, gravitating towards the koi’s requirements rather than settling on somewhere in between. By realising that as koi keepers, we are in a constant quandary, deciding between what is best for our koi and what is best for us as koi keepers who also view and maintain the koi pond. I strongly believe that we are too keen to provide what we want, willing to compromise what our koi need, often paying for it throughout the life of a pond with various koi health problems and ailments through the years.

So ingrained in the koi keeper’s psyche is the belief that filtered, clear and recirculating water constitutes a perfect pond, that we can overlook the pond conditions that our koi would actually prefer – namely a mud pond.

Why even consider a mud pond?

Putting it bluntly, if we kept koi for their benefit (rather than ours), then we would keep koi in a mud pond. A mud pond offers koi all of the environmental conditions they require and allows them to live and thrive in the environment for which they were created. Let’s not forget that koi are ornamental carp and consequently require the environment in which carp thrive in the wild. These fish prefer slow or still water bodies that have a high suspended organic and inorganic element.

They are regarded as the aquatic pig of a lake, where they use their sense of smell as their primary sense for locating food – rooting their snout deep into a soft and nutrient-rich silt (hardly achievable in a lined or fibre-glassed pond). We can choose to keep our koi in clear and filtered ponds but really that is taking advantage of their adaptable nature. Furthermore, so inbred are these ornamental carp, being intensively selected for their colour and pattern that their natural vigour and resistance to disease is greatly reduced; all the more reason for keeping them in natural, stress-free conditions.

The Japanese koi farmers of Niigata fully recognise the ultimate koi-rearing resource they have in their mud ponds and use them to their full potential. They rear their fry right through to their jumbo koi in self-sufficient naturally protective ponds. One of the greatest challenges that we as koi keepers face is to retain the vibrant colours and vitality at the levels we witness the day the koi were harvested from the Niigata mud pond. Our biggest problem is that our own clear and filtered ponds just don’t provide the same quality of environment as a natural mud pond and the colours and health tend to deteriorate as result.

What are the benefits of a clay pond?

There are many benefits to both koi and koi keeper if choosing to build a clay pond.

Easy to build. Firstly, a mud pond is easy to build, especially if as you say in your letter, your plot of land is clay-rich. A minimum clay content of 40% is required to make a clay pond watertight. The pond itself should be dug as large as possible, with at least three to four feet of depth. You must bear in mind that besides a little added aeration, the pond will be a still water self-sustaining ecosystem with no filtration. The larger you make it now the more stable it will be and the more koi you will be able to keep. Furthermore, think of the thousands of pounds you will be saving on pond equipment and other hardware.

Running costs. Even though the running costs of a traditional filtered koi pond are not prohibitive, in comparison, the running costs of a clay pond are negligible. You may have to use an air pump in the warmer months, but besides that you can leave Mother Nature to do the rest. There will also be considerable time-savings with pond maintenance, enjoying a very hands-off approach with a mud pond, something that can’t be said for a filtered koi pond.

Superior water quality. Even though the water in a mud pond may not have the appearance of what we would expect from high quality water, rest assured that the water quality in a natural and stable mud pond is ideal for koi. The minerals that are available through the clay substrate help to produce unsurpassed water quality that will support the life of all other aquatic organisms in your pond. With the addition of a little organic (pelletised chicken manure) and inorganic (super phosphate) fertiliser from time to time you can easily stimulate your pond to produce green water that will go on to support other live food organisms on which your koi will thrive. These are some of the practices used by Niigata koi farmers to enhance the productivity of their own mud production ponds. In fact the principles and practices of koi farming are the complete opposite to koi keeping in a traditional koi pond as we actively encourage green water by adding manure and there is no filtration or water circulation – Yet the results speak for themselves. The only significant cost for producing koi in such natural conditions is the poor water visibility. Even though the koi will be in the best possible condition, you will find them difficult to see ( but so will the heron!)

Superior quality koi. The completely supportive environment of a mud pond work together to produce koi in unsurpassed condition. The combination of the mineral and algae-rich water and the stress-free stable conditions all work together to produce growth and skin quality of the highest standard. We try to close the gap between a natural mud pond and our own filtered koi ponds by adding clay periodically and feeding foods supplemented with Spirulina (dried green water) but we rarely do we succeed at replicating what a mud pond can achieve for our koi quite naturally.

Breeding koi. If you are anticipating breeding and raising some of your own koi from fry, then by far the most effective way again is to harness the naturally supportive characteristics of a mud pond. The most challenging obstacle to breeding koi is not stimulating a koi to spawn, but to raise your fry up to fingerling size. The mistake that we all too often make is to remove the eggs to another pond or into an aquarium for hatching. This leads us to encounter problems such as finding the fry sufficient food of the right size and quantity so that they will grow naturally. Why work against what nature has already provided? The best resource for raising fry is to leave it to Mother Nature to feed them in a pea-green, organically rich, natural clay based pond. These are the conditions in which fry ‘expect’ to be raised and to which they are best adapted – so why try and work against it?

Clay or filtered pond?

We keep koi to look at and to marvel at their beauty. Hardly an argument for keeping koi in a mud pond. So if you have the space, why not utilise both methods for raising koi?

In this way, you will have the ideal resource in a clay pond for raising koi in their best condition, but also a clear and filtered show pond for displaying the beauty you have achieved in a mud pond in collaboration with Mother Nature. Your clay pond would also double up as a fry-raising pond as well as a rehabilitation pond for any koi that may be off-colour or have developed localised tissue damage. You will be amazed by the recuperative abilities that keeping koi in a mud pond can have on wounds or infections that would have otherwise warranted formalin and malachite treatment or hands-on remedial action. This is a phenomenon that I have witnessed myself when farming koi. The brood fish would be brought inside from a mud pond from February through to June until they spawned. By this time, even in the best possible clear and filtered koi ponds, the broodfish would start to look a little off-colour with the odd bruise or localised piece of inflamed tissue. After spawning, from June onwards through to January, they would be returned to an outside mud pond so that they would deposit eggs ready for next year. Upon netting the brood stock mud pond in January, those koi that were previously ragged or looking a little rough would be retrieved from the dark, thick water in the very best of condition – all courtesy of the mud pond.

The choices clearly yours, and your decision will reflect the extent to which you want to compromise between what his best for you and what is best for your koi.

Kill blanketweed and string algae.