The Annual Cycle of Nishikigoi

The Annual Cycle of Nishikigoi


From Toshio Sakai

“Spring / Summer Annual Cycle

There is an annual cycle in the life of Nishiki Koi. During the months of May and June, the female Koi tends to direct her stored nutrition and energy towards the development of her eggs. This is a natural and instinctive behavior for producing offspring. The caretaker must be particularly careful with increasing the food volume during this season.

It must be stated here, that while the water temperature is still low in May and June, the Koi does not utilize nutrition for body development. To an untrained observer, the fish might appear to have gained in its size, but in reality, it is filled with eggs in the fat stomach. It looks as if it had developed its body, but the body would be lacking in its basic physical strength.

If the Koi lives through this spawning season and the condition she is in, in the month of July, eggs turn into white empty shells. The more the spawning timing passes by, the more infertile eggs. After the spawning season it is natural instinct for the Koi to direct all its nutritional intake towards own body development. Hence, it should be known that body development can start only after the spawning period. Selected Koi are brought to Niigata mud pond from the concrete ponds of Isawa for their optimal development. It is important to decrease the water temperature gradually and prepare the body condition before introducing the Koi into the cooler mud pond. It is a challenge to feed Koi optimally during these three months. Depending upon how well the food was provided during these three months, there will be difference in the basic body strength. When the body grows, color becomes lighter; however, it is more important to build up the basic body strength, and if the body is solid, the luster will eventually develop.

If the fish can be fed properly and successfully during this period, then as the desired stage of growth and development approaches, the Koi will developed a highly lustrous skin. By feeding plentifully during the summer time, one can also develop Koi with graceful appearance in the way it swims in the water. Our experience has been that in the summer months, the saturation level of oxygen in the water is important for the Nishiki Koi health.? When water temperature rises near 86F (30C). Nishiki Koi food consumption diminishes.

In order to accommodate the increased food consumption and aid in the digestion, additional oxygen need to be provided. For the reasons stated above, well-mixed water with plenty of aeration is important. Often, pond water appears to be circulating well, but dead spots are not uncommon for any irregularly shaped pond; especially if they are deep. To summarize then, the ideal pond water for Koi health can be achieved by the infusion of a substantial volume of air, and generation of counter currents in the circulating water.”



Mr. Sakai has spent a lot of time experimenting with the growth, and development of his Koi. What he has discovered, I think, applies to all Koi. Developing a cycle is very important but what your goals are, with your Koi, will determine whether or not this is really something that you want to try.
Koi are four season, cold blooded, animals and to have them reach their full potential it is important for you to understand what they need through out the year to achieve it. I have said before that most of the issues, with growth, other than basic genetics, comes from feeding them the wrong amount of food at the wrong time and not being consistent. I think most people actually underfeed their Koi but also don’t understand when it is most important to feed. Temperature is very, very important for this to work though as Koi DO NOT process food in colder water. 70% of what Koi should consume comes in a period of the warmest months. This is usually from July to October.

One of the most important things Mr. Sakai points out is that female Koi can not direct any energy towards growth until the spawning season is over. This is at the end of June. Therefore, if you over feed your Koi, from April to June, then they will just develop eggs. A female Koi that has developed eggs will not grow well that growing season as she will develop eggs and then turn all of her energy towards absorbing the eggs.

It is important to feed very lightly from March to the end of June. If you feed you Koi enough to survive they will not develop eggs. If they do not develop eggs then they will grow very well from July to October. During these four months it is very important to increase the oxygen level in your pond and to feed them often. It would be best to feed them many times during the day rather than feeding them a lot a few times a day. They can only process so much at one time and the rest is just waste.
The growing season for Koi starts in July and is determined by the end of the spawning season.

From Mr. Sakai


“Autumn / Winter Annual Cycle

Water temperature in the pond varies from region to region. Nonetheless, for all regions one can expect the water temperature to go down starting in mid-September. Coinciding with this time of the year and drop in water temperature, Beni starts to increase its intensity. A large Koi is not known to develop well simply by the continued practice of usual feeding methods from winter to early spring.

What is most remarkable is that even if a large Koi is kept in a heated pond during the winter time, and then transferred to a mud pond to spend the spring and summer months, at the harvest time in autumn, the effect of such pampering on the fish will not be particularly impressive. The change of seasons, the natural environment, are all responsible for the development of a healthy and beautiful fish.

The natural environment with its seasonal changes, especially the cold winter, develops toughness and natural survival instinct in the Nihsiki Koi. These experiences will elicit habits of eating in the summer to store energy and strength to survive through the winter months. Moreover, it learns to develop the appropriate body mass for its age, again, in preparation for the winter. A critical point here to remember is, when the water temperature is low, it is best to provide food with reduced protein content and the total quantity restricted.We will talk more about it in the future.

Animals that hibernate instinctively know how to prepare for the winter and store energy to survive. They are all occupied to consume food in the summer to store enough reserves to survive the winter. A proper winter experience for the large Koi is very important for its development. For a cold-blooded animal such as the Koi, water temperature is of particular importance. The Nishiki Koi must sleep or less active in the winter. This is determined by nature. To go against it, and keep the fish in a very warm pond in the winter, will upset its bodily functions and balance.

The overprotected Koi is certain to disappoint the hobbyist in the fall harvest. If resourceful enough, one could experiment to see the differences between a Koi that experienced cold winter and a koi that did not. Even if these two differently cared fish are kept in the same mud pond over the summer and then their development compared at the harvest time in the fall, results will be as explained above.

In terms of Tosai, however, it does not have eggs and it is good to keep them in warm water and develop its size quickly. By doing so, one can see its potential quickly. Good Koi becomes beautiful and becomes very attractive quickly.”


I think it’s important to note that one of the things Mr. Sakai is saying is Koi will do better, with luster and growth, if given the four seasons rather than being kept warm and fed all year round. There is something about exposing them to the cold that helps with their strength and beauty that they can’t get from constant warmth and feeding. He has grown Koi both ways to study what happens. Koi kept warm and fed all year can put on good growth but over a long period if time they never exceed what there siblings achieve and, he states, that the siblings that are allowed to experience the four seasons do much better in the long run.
This brings up an intersting question. What do you do if you live in a warmer climate? I have recently been asked this by several of my customers and will ask Mr. Sakai when I see him in a few weeks.

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