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ATBAccueil Etang et bassin Les poissons et koï Oomo - Importance of osmo-regulationATB
Special article celebrating the grand opening of Koi Farm ND
< "Importance of “osmo-regulation” >
( Knowing about “osmo-regulation” can help a great deal in helping koi's health )
Nishikigoi Niigata Direct Ltd.
Niigata, JAPAN
Executive Director: Fujio Oomo
Director: Tamikazu Kobayashi
< Basic knowledge in koi keeping >

There is a Japanese saying, “koi swim up a water fall”, it describes well that koi have very good physical strength. They can live in wide range of environments - rivers, swamps, ponds – they can adopt to water temperature from as low as 3-4 degrees Celsius to 33 degrees Celsius.  It is generally  said that  the water temperature range that Nishikigoi like is between 24-26 degrees Celsius, but the range slightly differ according to their sizes.

From my experience, I'd say, for fry ( from 1cm – 10cm ), 27 – 30 degrees Celsius is the best for them to grow rapidly with best metabolism, this is also the best
Oomo koifarmND
omo koifarmND
temperature fro them to keep away from most diseases. And for koi over 10 – 20 cm, the best temperature range is between 25 – 27 degrees Celsius. For koi bigger than 20cm, the best temperature range is 24 -25 degrees Celsius.

This is my personal opinion based on my experience of koi keeping over 30 years.
< Please watch for stress koi get from a drastic changes in water condition and environment, sudden change in water temperature, or from getting moved from one pond to another. >
Nishikigoi can adopt to a wide range of water temperature and water condition if it doesn't happen too suddenly, but we need to take a great attention for stress from getting moved to one pond to another, or from the stress from transportation, or from sudden changes in environment, such as changes in water condition ( ph / Kh ).

 <Mainly, there are two factors that cause Nishikigoi to lose their condition >

A symptom that is caused by sudden changes of environment as I described before, koi lose condition from a drop down in ability to regulate Osmotic pressure in their system – not able to keep water out of their system efficiently. Let me explain, flesh water fish have organs that work  to pump out water out of their body fluid. Normally, the pump works efficiently to let out water flowing into body. But when koi are exposed to a stress from sudden changes of environment ( water condition, getting tired from transportation , etc... ), the function slows down, then symptom like “dehydration” in humans happen, and koi shows symptoms such as “sunken eyes”, “reddish body”, with blood vessels showing on the skin, or “swollen body”.

This symptom is different from diseases caused by virus or bacteria. This simply happens  when koi's physiological function is not able to keep up with the sudden changes. Although this is not  caused by diseases, it can lead koi to death.

We need to use “salt” to help koi recover from this symptom back to normal health       condition. Koi are freshwater fish, their body fluid salinity is 0.7%. So we need to raise the salinity level up to their body fluid salinity. In this way, it keeps water away from coming into their body. This is caused by “Osmotic pressure” ( water moves from low     salinity level solution to higher salinity level solution when two different solution are put  together. )

In this way, we can help koi to rest their body pump, and help them recover their body   organ functions. It is said that fish uses 30% of their base metabolic energy in “osmo-   regulation”, so we can help them save energy by keeping water salinity close to the salinity level of their body fluid.
In flesh water fish, the organs that have important roles in
  • “Osomo-regulation” ( osmotic pressure control ) are gills and kidnies. At the same time, gills play very important functions of
  • gill respiration ( taking in Oxygen and letting out Carbon dioxide ), and discharging body waste directly from gill  in a form of Ammonia.
So, when gill functions are slowed down, fish loses the functions of their main organ in sustaining life. In this very way, keeping salinity level of the water that fish swim in close to the salinity level of the body fluid of fish helps fish to better function in osmo-regulation, and this is an essential requirement  for fish to recover their condition. ( It is the same in human – when we suffer from heat stroke, or dehydration, we need to take salt and minerals as well as  we need to take water.)

Let me explain more specifically, please prepare 5-6 kg of salt per ton of water. A lot of times I talk with people having difficulty with their koi losing condition, I hear them say that they put salt in their pond, but when I ask in details just how many Kg per ton of water they put salt, they usually have 2-3 Kg per ton of water. It doesn't work at all with only 2 or 3 Kgs of salt per ton of water.
By all means, we need to use at least 5 kgs. of salt per ton of water – 0.5 % salinity.

By now, you understand that “Salt” helps a lot for fish to recover their condition, but it does not mean that 0.5% salinity kills parasites or bacteria as I am going to explain later. So we need to be careful to note this point. The point I'm explaining now about the effectiveness of salt is only to help fish recover their organ functions in time they lose condition.
( The use of salt as disinfectant  is described in a book “Manual to Nishikigoi” published by All-Japan Nishikigoi Promotion Association. )

  * Using 0.7% salt over a long period of time can be harmful to koi's health – it can cause serious damage in koi condition and may cause koi to die. Salt can be very helpful and brings great result when used in proper range of salinity level, but it also can be a “poison” when used beyond the proper range – as we humans, cannot exist without salt in our body system, but too much intake of salt can be very harmful to our health, also.  So if we consider this complicated matter in human terms, it looks more simple.

< It takes 5 -8 days for koi to recover conditions with salt in water treatment >
The days that takes for fish to recover depends on the stages of symptom ( whether the treatment was done  at the early stage, or it wasn't discovered and the treatment was done at     the middle stage, or at the very later stage and the koi were suffering much.)

It takes at least 6 - 7 days,  provided that the water temperature is 24degrees Celsius and the treatment was taken at the very early stage of “dehydration”. If the symptom was not discovered early and treatment was done very late,the rate of deaths raises much higher, and  salt treatment cannot be much effective. We need to be careful that there often are cases of  losing koi in this condition. We need to stop feeding  for 5 to 8 days and wait patiently until koi recover fully.

  < It is most important that we spot the changes in condition at the early stage, and give a treatment at the very early stage. >

In either cases  ( entry 1. or entry 2, which I'm going to explain later ) , it is most important that we discover the changes of koi condition at the early stage and give a treatment at the very early stage. Koi are worn out and there will not be enough energy left for fish to recover, if the treatment was  not given at the right time when the change was not discovered at early stage, or the first aid was not done properly. In this case, koi may die from multiple organ failure.

Therefore, it is most important to consider  whether the cause of the condition is from a  failure of the Osmo-regulation function, or from some diseases, or either a mix of some of the causes  ( Osmo-regulation function failure, parasites, bacterial infections, virus infections... ) and quickly determine how to give treatments.

2. Condition changes ( sickness ) caused by parasites or pathogens ( bacteria, virus)
Fish diseases can be put into three categories;

A)        Parasitic diseases
These are caused by parasites – some of them can be identified by naked eye, some  of them can only be identified by microscopic probe ( 200 x magnification )
  1. Anchor worms; most common parasitic infection. Anchor worms can be seen with naked eye when they are at an adult stage , but cannot be seen with naked eye at younger stages.
?Treatments; remove the adult anchor worms on the body surface of the fish. Then give a treatment with “Dimilin”(R) or “Masoten” ® into the pond water.

*Masoten is not affective with adult anchor worms, so you need ti give another treatment with Masoten 14 days after the first one. Dimilin ( powder ); apply 1g per ton of water – Dimilin kills adult anchor worms

2).  Fish lice (Argulus ); also most common parasite. Adult fish lice can be seen with naked eye. They are shellfish (crustacean) which stick onto the surface, fins and gills of koi.

?Treatments; These are easily killed with Mazoten ®.

3).    White spot, Trichodina, Costia, Dutilogirus , and others. These cannot be seen with naked eye,  need to be identified with Microscopic probe (200 x magnification).

?Treatments; Treatment with a mix of three component of disinfectants ( Formalin, Malachite green and Masoten is most efficient.  

< please do not mix up Formalin with Formaldehyde – I'm referring to Formalin as 40% Formalin. >

*When you use Formalin, please note that you need to check and make sure there is no salt in the water. If Formalin is used with salt in the water, it is very harmful – you can kill koi with this.

?Formula of this treatment is; take 20-25cc of Formalin, 0.2g of Malachite green and 0.5g of Masoten ( powder )  and dissolve into plenty of water and apply evenly to the pond water.

*<CAUTION> When giving treatments with Masoten, Dimilin and other disinfectants, cut feeding for three days - the day before, and the day of treatment and the day after. Also do not use Formalin in a pond with salt in the water.

B)             Bacterial infections, fungus and others;

You need to do microscopic probe ( 200 – 400 x magnification ) to identify the cause.
1)      Flavobacterium Columnaris, Aeromonas Hydrophyla, new hole disease, water fungus, carp pox, sleeping disease, etc...

?Treatments; for columnaris and  Aeromonas, can be treated orally with Oxytetracycline ( Terramycin ®  )

Water fungus can be treated with Methylene Blue or Malachite Green

Carp pox can be treated with Potassium permanganate (KMnO4) – apply Potassium permanganate solution to affected area.

Sleeping disease can be treated with raised water temperature (24 degrees Celsius) with salinity level of 0.5 % .

It seems there is no effective  medicine for new hole disease at the moment.

C)    Koi Herpes Virus disease (KHV)
There is no effective cure for this disease. Therefore, precaution is the most effective way to prevent this disease. Do not introduce koi from natural river or pond, when you buy Nishikigoi, it is strongly recommended that you buy from breeders,  shops, or dealers that takes KHV tests  periodically

(Nishikigoi Niigata Direct Ltd., takes KHV tests  every 6 months at a specialized institution.We have taken tests for over 10 years  - there have been no test results that came out positive .)
< There are cases which koi lose condition by eating too much >

In this case, stop feeding immediately and add salt to the pond water – 5kg of salt per  ton of water. It usually takes about a week for koi to recover a healthy condition. Please keep cutting the feeding until koi fully recovers the condition.

Nishikigoi are heterothermic animal ( animals that adopt to the temperatures of its environment and changes body temperature) and their  metabolism can go active or less active according to the water temperature they live in. Their metabolism go active in warmer temperature – about 24-28 degrees Celsius the metabolism stay at the top, and below 24 degrees, the metabolism gradually go down. So, it is better for koi's digestion to give less and less food as water temperature goes down below 24 degrees Celsius.  
(Koi have no stomach – they digest food and absorb the nutrients in their intestine. )

At water temperature 24 degrees Celsius, food they ate would be completely digested in about 5-6 hours (duration differ according to food to food). When water temperature goes down, as koi are heterothermic animals, metabolism goes down and digestive function also goes down, digestive enzyme also go down, and it takes longer for koi to digest food. So at 20 degrees Celsius, you'd want to give 20% less food than at 24 degrees. And at the water temperature of 18 degrees Celsius, better with a bit less food, then at 15 degrees, it is better to stop feeding completely – or give little food that is more digestive ( pellets with wheat germ, etc... ), for instance, once in every two days, give as much food as not to let them go skinny... when you try and find better ways, it makes koi keeping much more enjoyable.

Now that greenhouse pond facilities where you can control water temperature during winter are available, but for those who keep koi in outside ponds, during fall, when water temperature goes below 15 degrees Celsius, you'd want to cut feeding completely and wait until spring when water temperature goes up over 15 degrees and become stable, to start   feeding again, slowly and gradually. It is most adequate way for koi's health. Nishikigoi eat most amount of food in summer time when water temperature is high, and then September comes, and as water temperature goes gradually down, they store in fat in their body to prepare for winter hibernation. So after they come back from hibernation of the previous year, they eat a lot and store in fat in July, August and September to prepare for hibernation in the next winter.
  • This is an example for your reference -  water temperature and time of the year would somewhat be different from place to place, between climate zone you are in. But I would be most happy to give you some idea for your reference with these.
So these are a brief explanation about physiological functions, “Osmo-regulation” (control of osmotic pressure ) function, and treatments of fish diseases. In most cases, koi are easily affected by the stress from transportation, adopting to a new environment and lose condition after they get moved from place to place, in this case, please observe carefully and find the condition change as soon as possible and give adequate treatments quickly. In most cases, when koi lose condition, it helps koi to recover condition greatly to use salt in water as first aid – 5kg per ton of water.
Oomo in koifarmND
Oomo in koifarmND

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