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Nishkigoi by Jim Reilly

Updated: Fri, 9 Mar 2018

Nishkigoi by Jim Reilly

Nishikigoi by Jim Reilly

The Mission

To keep Japanese fancy colored carp, (aka Nishikigoi), in a way that allows the fish to meet its full long term genetic potential. The focus will be fixed on nutrition and husbandry techniques that blend with carp physiology, natural history and be consistent with the Japanese approach for rearing true tategoi. The result should produce colorful, healthier, longer living koi, with fine luster to the skin and conformation consistent with the standard for Nishikigoi.

The Natural History

We know that Nishikigoi are a mix of sub races of the common carp. The forbearer of the modern koi was a fish of temperate water conditions- not a true cold water species and certainly not a tropical species. The Chinese stock, the early domesticated Roman stock and the resulting European domestic carp, the wild European and Asia foundation sub races all have one thing in common. They experience seasonal change as part of their natural life cycle. The home of modern Nishikigoi is of course Japan. There, the mix of all the races mentioned as well as the gene pools created by released and recaptured feral carp were selectively bred in the mountain areas of Japan. The natural history of Nishikigoi then, is one of a temperate water species that has evolved with its seasonal surrounds. And these surroundings put a demand as well as a rhythmic cycle in place as an imperative for carp survival.

The carp is NOTHING if not a survivor! Blessed with an iron constitution, the domestic carp has an optimal range and a very broad and widely overlapping survival range. The optimal range is of the greatest interest to us because that is were the koi will flourish. The survival range is acceptable for food fish and survival of the species but puts little value on the individual well being. So the survival range is expressed as the minimal requirement for the SPECIES to survival while the optimal range is one in which the INDIVIDUAL will flourish.

The Physiology

Koi are very well tuned to their environment. As a primitive vertebrate, and being a cold blooded creature, its body temperature and metabolic system are much more influenced by surrounding temperature and other external parameters than say, mammals. This is why it is always a mistake to carry over dietary examples from dogs, cats and people to try and make intricate/integral points about diet and physiology of koi.

The koi’s metabolic rate in turn influences the dietary intake of koi. And of course, in the wild environment the availability of dietary items in both abundance and mix, are linked to temperature and seasons. This all comes down to metabolic demand at different temperatures. And that is made up of a series of hormonal shifts that open and close metabolic pathways as temperature changes. In concert with that, the shifting ratio of protein/carbohydrate intake acts as a feedback mechanism on those hormones. And so the battleship is turned. Slowly we see koi go from a period of rapid growth and high protein intake (animal protein) readily available in summer water to a lower intake of animal protein as the source or at least the quantity of protein begins to slacken. The winter is characterized by a starvation period in which the internal organs provide energy and the muscle layers provide amino acids. In spring, the dietary intake begins and the ratio of protein/carbs stimulates yet another hormonal surge and shift of metabolic pathways. This in effect, orders the body to divert energy towards gonad development. Once the breeding cycle has passed protein AND plant material intake moves the koi away from egg production and towards growth dedication. It is important to understand, that this is not a light switch but a gradual overlap in metabolic bias towards a primary survival function. Many of these survival functions emphasize the continuation of the species (i.e. breeding) and others enhance the survivability of the individual (growth and winter survival). Obviously we are interested in focusing on individual periods in the hormonal time cycle and less on future generation production.

The Japanese have an excellent handle on the rhythm of koi metabolic demands and in fact, call carp – FOUR SEASON fish. This means that koi are recognized as being different” beings” during each season in the mountains. This may be a little too “feely, Zen” for the scientific minded in the bunch but this idiot savant approach is strongly backed up by biochemistry and physiology. Every serious hobbyist in Japan understands this age old grounding of koi physiology to seasonal water temperatures/conditions. It seems to be lost on the majority of koi keepers in the West? Now most of the west, like my friends in the other Parish, are busy challenging the survival range of new imports and better adapted domestic stock. The more advanced hobbyists are moving in another direction.

Instead the slightly more advanced types are trying to beat the laws of nature. They’re doing things like, providing a perpetual summer, hiking protein rates to mimic the food fish production industry and judging success by how large a nissai can get in the shortest period of time. Those are all fun and interesting experiments, but at this point the “been there, done that, have the tee shirt” response can be muttered by most of the veterans. This always backfires but it can take impacted females, rugby shaped monstrosities, abnormal numbers of choman ( tumors) and washed out three year olds to humble most of us! The Japanese have it right, reduce the survival range to the optimum range. Match the diet to the koi’s natural hormonal cycle. Use temperature and diet to accomplish – not a perpetual summer, but rather, a stable spring, a long summer, a stable autumn and a muted short winter. Then match the food amount and mix to the metabolic demands of the season.

The Philosophy

If we understand the natural history and the physiology of the domestic carp we begin to appreciate that all the internal metabolic activity is designed and adjusted by, the seasons and diet. And that this is a feed back arrangement in the wild and in captivity/domestication. The domestic koi is very much “like” its fellow races of Cyprinus Carpio, but NOT exactly. There are differences in blood composition, shape of swim/air bladders, length of the gut, abilities to metabolism certain ingested material unique to domestic carp, storage of the amounts of certain vitamins and more. For the koi hobbyist that is all interesting but amounts to one practical observation. Nishikigoi are weaker versions of their “can’t kill’em with a bull dozer” cousin wild carp but ruled by the same environmental and dietary rhythms. The philosophy then, is an acceptance that koi are evolved to experience seasonal dietary and temperature change and in fact, NEED this change for normal metabolic cycling. Further, this philosophy will focus in on the optimal range of koi and avoid the broader survival ranges.

Let me give some examples: We can keep koi under ice, three months a year, feed them cheerios and brown bread and expect the majority to live. It’s true. Most will live. Some percentage will die- probably in a periodic fashion over the years, aeromonas and parasites will be part of the koi keepers experience on and off and the koi will be generally smaller than average adults over the same period of time. The koi might show small erosion marks on the face and head, the abdomens may be slightly distended and dropsy may show up now and then in the spring. Or we could heat koi to a constant 78-80 F all year round and feed high protein (40%) animal protein 365 days a year. All koi will live. Some bacteria infections will pop up here and there. Egg binding and miss shaped koi by the fourth year will be common. Koi will be large but not have strong conformation. Colors may look wasted out or exhausted compared to “seasonal koi”. And studies show that koi raised in this manner will not live as long as “seasonal koi”. You see this same thing with koi raised indoors in aquariums.

Under this philosophy we will envision carp as the Chinese and Japanese masters do. We will recognize that forced rearing is an industry tool for getting fish to the table or the consumer pond and is therefore an efficiency and economic approach. NOT evil in philosophy, just focused on short-term goals.

We will strive to first create the temperature change necessary to induce metabolic change and then match the food intake and mix to the metabolic demand of the koi at that time. A long summer, a stable autumn, a short and stress free winter, and a stable spring. Nishikigoi are four season fish.

The Technique The hobby has always pegged important temperature points that hint at, or identify “changes” in koi. Some of these points are parameter related (dissolved oxygen) and some are stress related (edges of the species survival ranges or term of exposure). So we often see the numbers in F as – 32F – death occurs if exposure is long enough 35F – the bottom of the survival range for the “unheated”! 45F- the bottom temperature recommended by many keepers 50F- the imaginary point where koi don’t digest food well 55F- the recommended bottom range by advanced keepers 88F- the range where adult koi show real metabolic stress

But if you look at the real world, these numbers attempt to reflect a linear decline or increase in temperatures. In truth, the real world is made up of peaks and valleys or swinging ranges of temperatures that trend downward or upward as the seasons come and go. The idea that a koi obtaining a pellet of protein food will keel over dead if that pellet is fed at 49 F is kind of comical when you think about it. But the idea that feeding below even 55 degrees has any beneficial effect on resting koi is also a bad joke.

I prefer to use the arrival of ‘zone of readings’ as the trigger to shift diet. Alternatively, the more casual keeper can choose a date each year to trigger the shift in the amount and mix of food realistically offered at that time of year. This is much more reliable in the unheated pond where quick chills, early frosts and warm Indian summers can really confuse both keeper and koi.

Of course, the person that heats has a huge advantage. There, a controlled decent in temperatures and an early control of spring temperatures is absolutely a quantum leap into state of the art koi keeping. Cooling with properly designed degassing units such as TTs is the technique on the flip side of the survival/optimum range for our warm weather keepers.

The size of a pond and its depth also plays in here. Large/deep ponds have more water volume and therefore don’t change as quickly as small shallow ponds. Calorie (heat) loss is huge at the ponds surface. Tenting is a valuable technique to slow this loss. The actual technique I recommend is to always assure a MINIMUM spread of 20 degree points F from the high point in summer water temps to the low water temperatures of winter. This must also hit a zone of low numbers that reflects a true slowing of the koi’s metabolism. That low would be a minimum of 55-60 F for six to eight weeks. The summer temperature for koi should not stay above 86F for any extended period. If you chart this 20 degree spread suggestion you will see where the bottom number becomes too high for true metabolic change and fasting. If you find that the highest top temperature is ONLY a 20 degree spread from a good resting number- say, 45F in winter and 65 in summer- you will sacrifice growth in the summer months and burden the filters with undigested protein. Please NOTE- I am not saying, repeat, NOT SAYING, that 20 degree swing is a target range! I am saying that a 20 degree swing is the MIMIMUM number to “reach” the koi’s internal clock. In a perfect world, all koi would have a 5 month “summer”, a 2 month” mild winter” and a short and stress free spring and autumn the balance of the year. The temperatures would be 76-80 F all summer, 60-68 in the spring and summer and 45-55 in the winter.

The withholding of food in an unheated pond is then linked to the level of koi keeping you pursue. We have already established that” most” koi will get by within their survival range. Water below 55 should signal the event of reduced feeding and 50F should signal the end of feeding. This has a practical aspect and a physiological aspect.

The withholding of food in a heated pond can be done at the “floor” temperature you prearrange as long as that absolute number represents a true starvation effect on the koi’s metabolism. I feed no food to my koi for six-eight weeks and keep the outdoor temps in the 45-50F range and the indoor temps in the 55-60F range. I feed very little (mostly Hikari wheat germ and my wheat germ paste food) in the stable autumn and Spring Periods.

A) The survival range for koi is 32F- 88F or 35F-86F depending on conditions and age of the koi

B) The optimum range for koi is more like 55F-82F

C) Most people with unheated ponds will overlap the optimal range and find themselves in the survival range. No problem, koi are tuff and can manage. You will notice that I let my outdoor koi stay as low as 45F which I admit is a bit too cold! And I never allow my temps to go above 78 F! The late Tom L must contend with temps in the very high 80's and even tickling the low 90s! The koi live! But if we don't understand the range limitations we all face from time to time, we miss the point/concept of metabolic change and metabolic demand within the koi.

D) So the seasonal extremes you mention represent wanderings of temperatures from a koi's ideal seasonal optimal range into their seasonal survival range. Once outside the optimal range do expect some problems once in a while. This is that population survival vs. individual’s survival model I mentioned in this series of posts. Within the optimal range expect very little in the way of sick koi. Living outside the optimal range continuously will likely result in real problems. Living outside the survival range continuously will result in 100% death, 100% of the time. All of us are blessed at one end of the optimal range and cursed on the other end. Too hot or too cold is the reason that advanced hobbyists have turned to heaters and coolers a long time ago.

E) Finally match the mix of food and the amount of food by the seasonal swing. The swing, ideally being a minimum of 20 degrees from seasonal high and seasonal low. With the final recommendation being that the winter low is at a level (45-55F) that slows the koi for a minimum of six weeks.