Rearing koi fish

Rearing koi fish

Koi fish are among the loveliest sights in a pond, especially if the garden is themed around the Japanese tsukiyama garden theme. These fishes represent wealth and abundance in traditional Chinese Feng shui beliefs, and it is believed by rearing koi, more wealth, health, and abundance will flow to the owner. Little wonder that koi fish are often extolled in many Chinese and Japanese art paintings.

Originating from China, but introduced to Japan and thus developed there (much like bonsai), koi fish rearing and breeding is now a high level art form, and many varieties and hybrids of koi have been developed in the past couple of hundred years.

Pond size

Many of the rules for a conventional aquarium apply to a koi pond; it is no different. A koi pond is just basically a water garden that you manage so that the koi fishes thrive. Decide where you want to position your pond. Decide on the size too. A modest size is adequate when first starting out, but remember koi can grow huge. Nonetheless, I have seen many ponds that would be considered small by purist standards; it is presumed the koi will be limited by the space, and not grow too large. A rule of thumb is to rear one koi fish per 250 gallons.

For ponds, something at least 150-200 square feet with a depth of 3 feet at least, to accommodate the koi which can grow to a size of about a meter, but more commonly, around 2 feet. The pond capacity should ideally be at least 1000 gallons. Choose a location that is safe from water runoff and has shade, because they need to take refuge from the sun. An indoor koi pond has many advantages over an outdoors one, but is obviously much harder to construct.

koi carp fish


Proper filtration is important because koi are “dirty” fish, much like goldfish (which they are related to). While you can certainly build your own filtration system, if you are a novice, it is better to leave most of the details to a koi pond stockist, who can recommend what sort of filter capacity is suitable for your pond. A koi pond filter is not really different from a typical aquarium filtration system; the difference is in the capacity. Different filters have different flowrates, but the filtration rate should be at least 50% of the pond volume per hour.

Do note there are basically two kinds of filtration in all full fledged filtration systems – A mechanical and a biological filter. Water first passes through the mechanical filter which filters out large sized debris and waste matter, and then proceeds through the biological filter, which contains bacteria to break down waste matter. The bacteria can be obtained from prepackages and seeded into the biological filter.

koi carp fish

Water pH

A water pH of 6-8 is acceptable for many fishes, including koi. A high pH reading means the water is too alkaline and can make your koi ill; lime leaching into the water from cement or bricks can cause this. Adding a pH buffer solution can help stabilize the pH level, because fluctuating pH levels are not well tolerated by all kinds of fish.

Koi need good water movement, which can be achieved with proper aeration. If the pond is large, several pumps may be needed. The air should be circulated from an airstone at roughly half the depth distance, minimally.

koi carp fish


Koi should be fed a high protein, high carotene diet, to promote their color and growth. Some of the best koi food products come with yeast to help with their digestion. Avoid foods with additives or artificial coloring/dyes that purportedly intensify fish color, as these are all bad in the long run. Give them chopped vegetables, like crushed peas or lettuce. During winter time, do not feed your koi, as they are go into hibernation mode, and will not eat anything.

Koi fish generally get hardier the larger they get, so it doesn’t really take too much effort to keep them happy and well fed. Worth noting, there have been many examples of long lived koi fish in Japan, whose owners did not have the high tech equipment that we have today; and yet, some examples of koi lived for many decades (in some cases more than 200 years)!

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