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Early Detection and Diagnosis of Koi Fish Diseases

Attention !! Related here is a very brief explanation only. Please check on the technical book for the details of diseases and their treatments.

Introduction - Koi Fish Diseases -

It is said that the optimal water temperature to keep Koi healthy is 24 ~ 25℃.

While, the water temperature that Koi-related bacteria is active and easy to proliferate is also 24 ~ 25℃. It is considered that various kinds of bacteria are living within the range of that water temperature in each season.

Parasites or bacteria are found in any pond water and in any fish, usually coexisting in peace with Koi harmlessly so far as the water is in good conditions.

However, Koi if under gone stress in an inferior environment, reduces its resistance to disease, bringing about an infection with parasites or bacteria outbreak under the bad conditions.

Detachment of scales due to bad handlings of Koi or any wound caused by collision against protrusions may sometimes result in an infection disease that develops by adherence of bacteria on the wound site.

Check Points to Detect Koi Fish Diseases

Watch fishes in whole, at the same time check each fish well on the following points.

If possible, check a fish body one by one everyday in detail to find abnormal in incipient stage.

How is water turbidity related to fish complexion?

Lightly greenish water with water-bloom is favorable to Koi health. But, cloudy water of higher turbidity will disturb appreciation or observation of Koi.
Such grayish, brownish or muddy water is not suited for Koi keeping.

Likely causes may be found in deficient capacity of settling in the tanks or filtration in the tanks, sludge accumulation, shortage of new water, shortage of dissolved oxygen, overcrowding, too much feeding and etc.
Examine water quality carefully (pH, ammonium, nitrite contents etc. )

How is grouping ?

Koi, separate from group into the corner or the bottom of a pond, floating near the water surface, or gathering around the pouring pipe(inlet) or drain outlet, are all in bad shape.

Could be a bacterial cause disease.

Is there any Koi with strange swimming ?

There must be something abnormal with a Koi, that rubs against the wall or the bottom of a pond, flaps up frequently on the surface, collides against the wall, trembles all over or swims crazily.

Suspect parasites.

Have a good appetite ?

Observe whole groups of Koi to check if there is any not coming for feeding.
Also, check if there is any food left uneaten.

Decline of water temperature, lack of oxygen, increase of ammonium or Nitrous acid level, parasites or bacteria origin infection, or visceral disease could be causes of KHV.

How is Koi's dropping ?

Examine Koi's dropping if it is floating on water, or abnormal in color, or transparent or not.
Dropping, of a few millimeter in length, which sinks in no time to melt in water is normal.
Floating dropping, continuous dropping or gelatinous dropping are not normal.

How is body appearance?

Keep careful watch on such symptoms as congested fin or abdomen, abnormal in color, tumor, ulcer, abnormal cloudy body surface, skinny, swell, bend, eyeball pop-up, sunken eyeball, fin's tear or melt, external wound, parasites, abnormal breath, presence or absence of scale- rise and its state, attachment, protrusions, and swell of gill cover etc.

When gill cover is opened sometimes change in color is detectable.

Check it very carefully.

Koi Fish Diseases

Koi Keeping Outdoors

An outdoor garden pond is the ultimate setting for fully appreciating the beauty and elegance of Nishikigoi.

The optimum environment for koi is a recirculating system that has good filtration, both mechanical and biological.

Outdoor ponds can be counstructed with concrete, fiberglass or even vinyl sheeting.

With the development and availability of efficient ready-made filtration systems, it is possible to enjoy koi keeping in any setting, from traditional Japanese style gardens to modern ponds designed strictly for raising koi.

Koi Keeping in an Aquarium

Like tropical fish, Nishikigoi may be kept in the house.

Then, you can be close to them and by viewing them from the side, can appreciate a new charm in Nishikigoi.

Small-sized Koi are particularity suited for keeping in the house, and if they become too big they can be kept outdoor.

Koi keeping on a Veranda

Nishikigoi may also be kept on verandas.

The space is much larger than that available in the house and the Koi can grow much bigger.

The aquarium is equipped with a filter so even if you have no garden, it is possible to keep Koi as if you are keeping them in a pool.

Koi Fish Disorder Discovery

Detection of Koi Fish Abnormality

If the following symptoms are found, check up possible diseases out of the assumed fishery diseases to examine whether they are incipient or terminal disease signs.

Check for abnormal grouping and swimming

Unnatural behaviors are observed in grouping and swimming, when something abnormal affects their physical conditions.

Hang out at water inlet

Hole disease, White spot disease, Myxobolus koi infection, Gyrodactylosis, Dactylogyrosis, Chilodonellosis, Scale Extrusion disease, Ichthyobodosis, Columnaris disease, Dropsy, Apiosoma

Gather around drain outlet

Chilodonellosis, Dactylogyrosis, Gyrodactylosis, Dropsy, White spot disease

Fall away from grouping and stay still in a corner

Gill disease, Argulosis, White spot disease, New gill disease, Columnaris disease

Not going for food

Argulosis, Scale Extrusion disease, Hole disease, Ichthyobodosis, White spot disease, White cloud disease, Chilodonellosis, Dactylogyrosis, Gyrodactylosis, Myxobolus koi infection, Columnaris disease, Intestinal thelopanellosis , Apiosoma

Motionless in the pond bed

Argulosis, Hole disease, Myxobolus koi infection, Gyrodactylosis, Dactylogyrosis, Chilodonellosis, Trichodinosis, Ichthyobodosis

Lying down dormant in the pond bed

Sleeping disease, Common cold

Inactive and standing still

Argulosis, Myxobolus koi infection, Chilodonellosis, Dactylogyrosis, Gyrodactylosis, Columinaris disease, Apiosoma, Dropsy, White cloud disease, Common cold, Intestinal swell

Floating on the surface

Argulosis,, White spot disease, Myxobolus koi infection, Gyrodactylosis, Dactylogyrosis, Chilodonellosis, Trichodinosis, Ichthyobodosis, Columnaris disease, Dropsy, Apiosoma

Rubbing against an object

White spot disease, Anchor worm infection, Argulosis, Epistyliasis, Myxbolus koi infection, Gyrodactylosis, Chilodonellosis, Ichthyobodosis, Columnaris

Jiggling pectoral fins and dorsal fin

Anchor worm infection

Violent erratic swimming

pH decline, Argulosis, Anchor worm infection, White spot disease

Madly and unbalanced swimming

White spot disease, Bubble disease, Dropsy, Columnaris disease, pH decline, Electric leakage

Abnormal jumping up above the surface

Anchor worm infection

Healthy Koi usually sleeps pectoral fins opened, but closes them if any disorder with it.

Check the way of Koi Fish Death

When Koi is found dead, make a due examination of its gills, mucosa and outer appearance. Discoloration of the gills will occur in an hour after death.

Therefore, the examination should be made not on the dead Koi but on the other one on the verge of dying.

Sudden death of Koi in bulk

Lack of Oxygen, Poisonous substance, Columnaris disease, Red spot disease

Several fishes die every day

Columnaris disease, White cloud disease, Water molds, Other parasite or bacteria

Not noticing of on the day before, but a few fishes dying daily

Columnaris disease, Gill rotten disease

Dies in frantic state

Columnaris disease

Koi hang out at water inlet and dies

Columnaris disese, Myxobolus koi infection

Koi gathered at a drain outlet and dies

Gyrodactylosis, Dactylogyrosis

A slight reddish discoloration of the body surface occurs before dying

Columnaris disease

The bigger and fatter ones die first

Shortage of oxygen

How to Check Diseases of Each Koi Fish

Every fish disease assumes different symptoms in incipient, middle and terminal stages.

Of course, the disease at incipient stage is easy to recover, while Koi in the terminal stage not recover easily,and are not worthy of admiration, even after full recovery.


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Abnormal Koi Fish Surface Checkup

Abnormal symptoms appearing on the body surface vary ranging from opaque, hyperemia, parasitization, pine cone surface, hole surface and many others.

Opaque mucus on the surface, that appears covered with thin white cloud

White cloud disease, Chilodonellosis, Ichthyobodosis, Incipient white spot disease, Trichodinosis, Gyrodactylosis

Removal of mucus occurs exposing the coarse surface

Chilodonellosis, Gyridactylosis

The surface is opaque and cloudy

Gyridactylosis, White spot disease, Cold

Abnormal secretion of mucus causing to appear cloudy

Bacterial white cloud disease, Gyrodactylosis, Columnaris disease

Numerous white spots as small as a needle's eye can be seen on the surface

White spot disease

Hyperemia and bleeding

White spot disease, Chilodonellosis, Ichthyobodosis, Trichodinosis, Gyrodactylosis, Argulosis, Scale extrusion disease

Scales are worm-eaten, with small white spots on the body surface


Red congestion with fins and whitish discoloration occurs from the top of the fin, melting like a broom

Columnaris disease

Detachment of scales and mucus occurs, making the fish appear as if covered in white rags

Columnaris disease

Fungus attached over the body surface

Hole disease, Fungus disease

Fungus are noticeable at the dorsal of the body


Heavy hyperemia in a small area


Scales appear like pine cones

Scale extrusion disease, Hole disease, New hole disease, Epistyliasis disease, White cloud disease, Common cold, Intestinal swell

Holes are found in the fish body

Hole disease, New hole disease

Hemorrhagic reddish splotches and ulcer appear on and under the skin

Hole disease, New hole disease

Juvenile fish body is swollen, looks transparent

Dropsy, Columnaris disease

A piece of scale-sized flesh protruding

Parasite prints flaw

Body surface bleeding of juvenile fish


Swollen abdomen

Scale extrusion disease, Intestinal Thelohanellosis of koi, Common cold

Tumor of white or pink-tinted wax is observed


Discoloration and protuberance is noticeable only in red patterns

Hi-kui disease

Translucent and rod-shape parasites, 5~10mm in size are sticking

Anchor worm disease

Transparent and disciform parasites, 5mm in diameter are sticking


Bleeding at anus, appears red

Too much feeding, Intestinal swell

Slight skin protuberance of 1~2mm high observed

Dermal thelopanellosis of koi

Tiny bubbles are formed in the fins, head and around the eyes

Bubble disease

Erosion of surface skin exposing flesh

Common cold

Faded in color

Intestinal swell


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Abnormal Koi Fish Figure Checkup

The body form changes is apparent to the naked eyes, resulting in easy and early detection.

Abnormal swell of abdomen

Intestinal swell

Abnormal pectoral swell, with hanging belly which is partly constricted

Breast swell, Two-tied abdomen

Losss of flesh at the dorsum and very slim appearance

Chilodonellosis, Intestinal swell

Deformed Koi in S-shape, Shachihoko-form or akimbo


Eyeballs pop-up

Scale extrusion disease, Intestinal swell

Sunken eyes

Dropsy, Sleeping disease, Columnarisis disease

Eyes are rotten and festered

Hole disease, Columnarisis disease

Showing necrosis in mouth, gills, and fins, rottening and tattered

Columnarisis disease

Abnormal shape, with convulsion and windingl swimming

Atropheid loin

Abnormal Koi Fish Gills Checkup

The gill does not allow easy checking of the inside, except possible speculation about the presence of anomaly judging from movement of gills cover.
Besides, erratic form of gills cover can be seen outside.

Whitening around the gill

Chilodonellosis disease, Dacylogyrosis

Abnormal secreting of mucus causing discoloration of gills and whitening

Gyrodactylosis, Dactylogyrosis, Ichthyobodosis, Chilodonellosis, Trichodinosis, Myxobolus koi infection

Discoloration of the root of gills and whitening

Columnaris disease

To open the operculum, the gills look whitish

Columnaris disease, Apiosoma

The gills become partly gray white and center part is gray or yellow and degenerated, or disintegrated

Columnaris disease

White gelatin-like substance appearing at the peripheral part of the gills

New koi-disease

The gills appear swollen

New koi-disease

White-flecks or white spots are visible on the gills tissue

Myxobolus koi infection

The operculum remains open

Myxobolus koi infection

Discoloration of the gills into reddish black

Myxobolus koi infection

Discoloration of the gills into snow-white

Herbicides Damages

Abnormal Koi Fish Body Surface

There are various kinds of abnormal body surface. Pick some mucus on the surface to study by using a microscope. Start examination at lower magnification ratio, then raise the ratio little by little.

Abnormal Fins

Check for congestion of the pectoral and abdominal fin, i.e. presence or absence of red lines.

Abnormal Gills

Open the gil1s to examine.

When mucus on the surface is normal, cut off a few pieces of gills to examine by using a microscope. Apply a light anesthetic at the time of cutting.

But, the gill will discolor into white within one hour after death. No cause of death be detectable after discoloration.

Visceral Koi Fish Abnormality

If you are well-acquainted with the normal entrails of Koi through your experience, dissect Koi to check for visceral abnormality.

If not experienced, try dissection on both Koi, sick and healthy ones at the same time just for comparison.

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Koi Fish Disease

~ "Salt-Bathing" Recommendable ~

Let carps free in the water for 4 to 7 days, wherein 6-kgs salt and 5-grams "Elvarjyu Ace" are mixed up per 1-ton water. (Adhere to the ratio of water, salt and medicine)

After 4 to 7 days bathing, release them.

Do not feed while bathing in salt water.

*Carp producers or traders do carry out this salt bathing carp without fail, even in case of transfer under the same facilities. Advisable to effect salt bathing whenever undergo changes in circumstances.

Koi Carp

Pond Water Preparation for Nishikigoi

People say "Make water before breeding Nishikigoi"

It may be said that water for Nishikigoi means more than air for man.

To let Nishikigoi lead a long life in good shape, it is inevitable to make water just suited for it.

Those who are intending to participate in the Show, or take Nishikigoi as a kind of art are invited to study for the best water-making just for Nishikigoi, to bring out its features of its own.

Water in Nishikigoi ponds is very important. Please pay your best attention.

Koi Fish Disease

First-Aid Against Koi Fish

You might have to make an immediate disposal or absolute quarantine of Koi, depending on the kind of disease infection, for all-out.disinfection of the disease origin.

Some diseases have still no cure due to unknown causes.

Abnormal with one or two fishes only, while others are normal. In that case, you may set them apart from others and guess a likely disease to take proper measures.

Sooner of later, however, almost all diseases are infectious, so it is desirable to give medication to a pond as a whole.

First-Aid for Whole Koi Fish in Abnormal State

Once you have seen something abnormal with the whole fish, take the following tentative measures for a pond.

The pond installed with filtration devices

1. Change the pond water by 2/3 or 3/4.

2. Lightly clean the filtration tank just by watering.

3. Stop feeding or new water supply or both.

4. Keeping no new water supply, put 25cc formalin and 0.5g Mazoten-powder to 1-ton water and allow circulation. At that time, do not fail to give thorough aeration.

5. After the elapse of full two-days, disperse 6kg salt and 50g Terramycin(or 100cc BarazanD) to 1-ton water.

6 .If no recovery signs come out even after 7-days, again change the pond water by 2/3 and put another 4kg salt additionally. Since the old water already contains 2kg salinity, the total volume of salt will come to 6kg to 1-ton water.

7. In case no recovery signs are seen even after 7-days, please consult a dealer or specialist.

The pond, water pooled and no filtration devices installed

1. Change the pond water as a whole.

2. Stop feeding.

3. If about 3-days seclusion of Koi is possible, first conduct disinfection by chlorine, then fill the pond with new water, where Koi is released. In case such seclusion is not available, clean the pond thoroughly, and refill it with water immediately. Please do not fail to adjust the water temperature prior to fishifying.

4. Perform medicine-bathing treatment as per the procedures for "The pond installed with filtration devices".

The pond, with no filtration devices installed but incessant water flow available

1. Change the whole pond water .

2. Stop feeding.

3. Conduct medicine-bathing treatment following the procedures for "The pond with filtration devices".

First-Aid for Unknown Koi Fish Disease and Its Checkup

When a disease name is still unknown, take the following tentative measures. After implementation of measures required, please check the following points.

First Aid

Stop feeding.

More new water supply than usual.

Increase the amount of oxygen supply.

Checkup Items

Back to the basics of feeding, reflect on the food if new or not, or feeding volume was proper or not, or suited for water temperature or not.

Also, restudy if the pond is overcrowded or not, taking into consideration the volume of pond water, oxygen supply level, and filtration efficiency.

Check the filtration devices or settling tanks if they are stained badly or not.

Additional Measures for Poor Koi Fish Curative Effect

If no good results are obtained even after one(1) week, take another steps for treatment, assuming a disease of like kind or complicated.

First, change the old water by around 2/3.

Add salt in proportion to the volume of water disposed, if needed to keep salt-bathing effect.

If necessary, give an additional treatment of medication with several kinds of drugs duly combined, subject to a prior checking of drug combination.
Some drugs may not be dozed together.


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