Diseases in pond Koi fish

Diseases in pond fish

Fish are the best indicator of the health of a pond. When something goes wrong in the pond, pond koi fish multiply at an alarming rate.

So, in this post, we’ll talk about the causes and signs of different diseases, explain some of them, and give tips on how to avoid and treat them.


Let’s begin by looking at the causes of fish disease. Most pond fish diseases can be traced back to poor husbandry parasites.

Some examples of this are:

  • There is a lack of food.
  • The value of water is insufficient.
  • A pond that’s too small.
  • The stocking density is too high.

The fish’s defense mechanisms weaken as a result of the stress. Infectious diseases like parasites and bacteria are more likely to spread. Newcomers often bring diseases with them when they move to a new place.

Because of this, new fish should be quarantined in a separate tank, where they can be monitored for abnormalities before being released into the pond.  Many diseases can be spotted early if pond owners keep an eye on their fish on a regular basis.

You’ll be able to more easily identify anomalies.


If you know what to look for, it’s often not that difficult to spot diseases in their earliest stages. To begin, there is a behavioral shift:

for example, there is a loss of the ability to flee, a lack of hunger, or a lack of desire.

standing or lying on the ground for an extended period of time. Stumbling and standing on your head are two signs of swimming problems that are easy to spot.

If a fish is rubbing its body against the ground or the edge of the pond, it is more likely to be overlooked as a sign of  illness.

Fish, like humans, can get itchy and jump out of the water from time to time.

In a normal pond, it’s hard to see fast gill movements, but it’s easier to see emergency breathing on the surface of the water.

The physical changes that occur as a result of disease are numerous. Skin pigmentation, emaciation, and changes in body shape are all examples of these changes. This is not an all-inclusive list. Because, of course, other symptoms may emerge depending on the disease.

Waterborne pathogens can rapidly multiply and spread. So if you notice any of the early signs of a disease, don’t hesitate to take action!


In the case of a disease, you may be able to treat your fish at home with salt baths or over-the-counter medications from your local pet store.

Subtle changes in water temperature can be very beneficial. When treating a disease, a diagnosis that is as accurate  as possible is essential!

It’s impossible to find a “one-size-fits-all” drug that can treat a wide range of conditions. It’s a waste of time and money to give your fish medicines they don’t need, which can cause them to become resistant.

Consequently, we recommend that you seek the advice of a fish veterinarian if your pet becomes ill. He can treat your fish specifically and give you sound advice.

Pond koi fish diseases you should know about

The following examples illustrate fish diseases and their treatments:

Prior to beginning any treatment, we recommend consulting with a fish-only veterinarian.

For your fish’s sake, unnecessary and incorrect therapies should be avoided at all costs if you want to make a precise diagnosis.

(Ischthyophthirius multifiliis) The White Spot Disease

The typical white spots on the mucous membranes of its hosts are caused by this one-celled parasite.  In rare cases, the fish’s eyes can also be infected.

Shortness of breath is a symptom of gill disease.

The lengthy Latin name for a single-celled organism is frequently shortened (“Ichthyo”).  Ichthyo is exploding in numbers.

From time to time, the white pocky growths fall to the bottom of the aquarium.

Swarmer-infected fish become infected again after about 24 hours, depending on water temperature.

The sooner you begin treatment, the better.

Even though it is possible to use malachite green as a therapy, it must be done over at least five days. A longer treatment period may be required in some cases.

Costia (Ichthyobodo necator)

These cloudy skin parasites are typical of those who are weak. There is very little chance of unicellular organisms  causing harm to healthy adult fish.

In contrast, flagellates have an easier time infecting pond dwellers that are still young or have been infected by other diseases.

Pests thrive in water that has cooled to less than 15 degrees Celsius. It is at this point that the parasites irritate the mucous membrane and cause swelling.

A white-blueish shimmering opacity develops as a result. They open the door to additional infections, such as fungi, by causing damage to the mucous membrane.

As a result, a large-scale infestation is often fatal.

Treatment with salt baths can be sufficient in some cases.

They aid in the fish’s metabolism, which in turn stabilizes their immune systems.

However, research into the underlying causes must be conducted prior to any drug treatment. Because it is very important in Costia to treat and get rid of the root cause of an immune deficiency,

If you don’t get rid of the parasites, you’ll only inflict more pain on yourself. Your trusted fish veterinarian should be contacted if you have any questions. Flukes ( Gyrodactylus spp., Dactylogyrus spp. )

These minuscule worms can be a real pain for the fish in your pond. They are generally invisible to the naked eye.

A microscope is the only tool that can reliably detect it. Skin eye worms (Gyrodactylus spp.) and gill eye worms (Gyrodactylus spp.) are distinguished (Dactylogyrus spp.).

In most cases, this worm lives on the outer layer of the skin. In addition to causing damage to the mucous membrane layer, it also serves as a trailblazer for other issues.

Algae and fungus can grow in the scaly pockets, causing irritation. Animals with affected skin may appear cloudy when they scrub or jump.

Gyrodactylus does not lay eggs, unlike Dactylogyrus, which lays eggs in its eggs. Most of the time, but not always, the egg-laying gill suctionworm can be found on the fish’s gills.

The irritated and swollen gills of infected fish make it difficult for them to breathe.

Flukes are well protected against them.

Simple salt baths often help with mild infestations.

Using products from pet stores (after consulting the package insert) is an option once a definitive diagnosis has been made. Or the veterinary medicine prescribed

Avoid using antiparasitic medications that aren’t absolutely necessary. Otherwise, the promotion of resistance will  take place!

Carp louse ( Argulus sp. )

Carp lice are crustaceans, despite their name. It is possible to see these parasites up to a diameter of 13 millimeters with the unaided eye.

They’re often spread by waterbirds. They cling to the skin and the pockets of flakes. A reddening of the skin as a  result of bleeding or inflammation could be one of the side effects of an infestation.

Itching is a common occurrence. As a result, afflicted fish may, for example, scrub themselves or shoot through the pond completely.

It is possible to collect individual carp lice. If the infestation is severe, medication must be used to treat it.

In-store remedies and medications from your fish-savvy veterinarian are both options.


Fish mold ( Saprolegnia parasitica )

This disease is almost universal. As a general rule, healthy fish with functioning immune systems can’t be harmed by this. When the immune system is weakened, things can go away. For instance, as a result of the winter’s extreme cold.

Saprolegnia can also get into the fish’s mucous membranes if they are irritated and scratched. It’s not uncommon for this fungus to take hold of wounds that have been infected for a long time.

Cotton-like coverings are the most common form.  At first, they’re white, but over time, they develop a greenish-gray coloration.

In addition, fish spawning grounds are particularly vulnerable. Fish mold is a common problem, and it frequently results in large financial losses.

Fish mould can be treated with commercially available malachite green remedies. Shorter, more frequent salt baths can provide relief.

Bacterial diseases

Bacterial diseases in the pond can manifest themselves in a wide variety of ways and progress at varying rates.
Bacteria, which can infect fish, are practically nonexistent in this environment. Bacteria found in ponds are the most  common source of bacterial diseases, and they usually do no harm.

It is possible for these bacteria to cause disease if the stable system is disrupted. The symptoms of the diseases that  result from this are used to name them.

“hole sickness”

A common cause of “hole sickness,” also known as erythrodermatitis, is a bacterial infection. As is so often the case, other pathogens and inappropriate environmental conditions are to blame. On affected animals, large, ulcer-like skin holes can be seen. The caudal fin is located at the back of the animal’s trunk or a little further back.

The diseased fish’s muscles are sometimes visible from the water’s surface. The disease can spread quickly, depending on the cause and the surrounding conditions. It’s not impossible for people to die suddenly and terribly. Consult a fish veterinarian right away if you suspect anything is wrong with your fish. With the help of a smear, he can find the pathogen, test for resistance, and start the right treatment. “Fin rot”

Fin rot is evident by the appearance of frayed or discolored fins, as well as a milky or red discoloration on the fin tips. The fact that this illness is common shows that living conditions are not up to par. Individual fish may be affected only in a small area on occasion, and this is usually due to a wound.

This disease necessitates a veterinary examination and treatment. Before choosing a treatment method, it’s important to do a thorough diagnosis to make sure that other pathogens aren’t to blame. You can’t fight the disease unless the causes are fixed and living conditions are made better.

Viral Infections

Koi herpesvirus (KHV)

A disease caused by the Koi herpes virus has been documented for the past two decades.

It must be reported as a contagious disease. Massive damage to the gills is the most obvious sign of this disease’s presence.

In addition to the central nervous system, the virus has the ability to infect the skin, digestive tract, and kidneys. Invisibly, the fish become infected.

As a general rule, the disease is brought on by stress and temperatures between 16 and 28 degrees Celsius.

The skin can be damaged. Other diseases are more likely to affect animals. The most obvious sign that your gills are damaged is that you have trouble breathing often and very badly.

The fish use the water’s surface or the filter vent as a source of oxygen. It is possible for large numbers of people to  die. It is not possible to conduct a causal analysis.

The only option for sick fish is to keep them in isolation while the conditions in the tank are optimised.

The veterinarian takes a small piece of tissue from the fish’s gills to test for the Koi herpes virus with PCR.

Except for the carp, all the other fish in the pond appear to be unaffected by the virus.

Carp pox (CHV-1)

Occasionally, carp pox or koi pox can be seen in ponds where the temperature has fallen. They can be seen as white, waxy deposits on the skin or fins, depending on the species.

Whenever an infected animal’s immune system weakens, especially in poor environmental conditions and in water  that is too cold (12 ° C), the small growths on their bodies multiply.

Due to the fact that the infected fish are constantly shedding the virus, there can be no true “cure.” However, it is possible that smallpox will be eradicated.

If you have any of these, don’t worry about it. They’re just blemishes. They only cause serious harm in rare and  exceptional circumstances.

Other Health Issues

Swim bladder infection

The most obvious sign that a fish has swim bladder inflammation is that it can’t control its buoyancy.

The worst-case scenario is that the animal remains motionless on the pond’s bottom. Fin power is all it has to get it to go up and down. It soon develops callouses as a result of this constant exertion of force.

Individual animals are usually the only ones affected. It is common for infections to be caused by parasites, bacteria, or metabolic disorders. A qualified veterinarian must determine the appropriate treatment method based on the underlying cause.

Increasing the water temperature to around 25-27 °C and adding iodine- free table salt to support kidney function usually helps, regardless of the cause of the swim bladder infection.

Animals that have been sick before are more likely to get swim bladder problems again.

Energy Deficiency Syndrome (EMS)

An energy deficiency syndrome is a common spring illness.

It happens when there is a difference between how much energy is needed and how much is actually available. The lack of energy could be due to a lack of food in the summer or early feeding in the winter months.

The development of EMS is also aided by water with a low concentration of oxygen. Animals that are severely  malnourished and emaciated are particularly vulnerable.

Because they can’t use their fat stores when it’s cold, fat animals are more likely than lean ones to get the energy deficiency syndrome.

The EMS-infected fish display an uncoordinated swimming style, slowed reactions, and shallow breathing.  Your kidneys are unable to perform at their full capacity, resulting in water retention in the body cavity. It’s not  uncommon for affected animals to appear bloated and swollen during examinations.

Protruding like a pinecone are the scales. It’s as if his eyes are protruding from his face. Slowly warming the water by no more than 2°C per day and adding moderate salt helps animals with EMS.

The fish can be fed a high-digestibility diet as soon as its behavior returns to normal. There’s no time to waste when it comes to EMS!

Prevent fish diseases

Deaths happen frequently. Eliminate fish pathogens. It’s better to be safe than sorry!

Because, as previously stated, the disease can quickly spread throughout the pond and even be fatal in some cases.  To avoid this, make sure your fish have the best possible living conditions.

Keep an eye on the water quality and the filtration system to ensure that it is safe. The pond’s size should correspond to the number of fish kept and the specific needs of the fish you intend to keep there.

Maintain a healthy weight by following a well-balanced diet. Food should be stored in a place that is cool, dry, and free of odors.

As a result, it will not go bad before it has a chance to. Adding vitamins to the diet may be beneficial in some cases. Make sure to get in touch with a reputable fish vet as well.

There’s no need to waste time looking for a veterinarian if you already know his phone number and email address.

Preventive pharmaceutical treatment of your fish is not recommended.

Unnecessary treatments put the fish at risk and may even cause the pathogen to develop resistance. This must be avoided at all costs! On the other hand, routine preventive exams make perfect sense. Several fish veterinarians offer spring and fall check-ups for their clients.

When you’re in transition, you have a clearer picture of your patient’s health status and thus feel more secure.

Then again, you can and should keep an eye on the water levels on a regular basis yourself.

You can take preventative measures early on if you notice changes in the negative. Aeration of the pond can be accomplished by using air pumps or the filter vent.

It improves the fish’s ability to deal with unexpected stressors. Temperatures below 32 degrees Fahrenheit should be avoided at all costs, unless absolutely necessary.

Keep an eye on your fish at all times. The more you learn about their natural behavior, the more quickly you can identify signs of illness.

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