Pond fish diseases

Pond fish diseases

What are the various pond fish diseases and how can you combat them?

A lot of pond owners believe that fish diseases are mainly introduced and passed on by sick fish. Fortunately this is very rarely the case and it’s mostly within your control whether your fish keep well and fit. More than 90 % of the diseases are caused by inappropriate living conditions, such as water values and inadequate nutrition!


On the JBL website you will find the Online Hospital which gives you a complete outline of the diseases (including diseases in the aquarium) with over 500 pictures.

Fish diseases

In case your pond fish fall ill, we will show you which disease it is, and how to combat it reliably here.

Identification of fish diseases

Describing fish diseases is not easy. This is why we have collected hundreds of photos, which can help you to identify a fish disease. Have a look at the Online Hospital . There you can diagnose a fish disease using photos or identify them with the help of an identification key. A click on the photo of the disease will lead you to the corresponding fish disease and refer you to the treatment, as well as to any possible mix-ups.

Triggering factors of fish diseases in pond fish

Although fish diseases in pond fish are caused by parasites, bacteria or other pathogens they are often triggered beforehand by other factors. Thus the fluctuation of the pH level of your pond water (with low pH 6 in the morning and high in the evening) can result in a weakening of your fish, and their weakened immune system makes the infection through pathogen germs or parasites possible in the first place. If we compare it to humans it illustrates the situation well. We are also more vulnerable to illnesses when we are extremely stressed.

Therefore a stable aquatic environment and good nutrition are the best preventive measures against fish diseases. Combat fish diseases with the suitable medication and afterwards check your water parameters to find out the cause. Consider changing the diet of your fish to a high quality food, which exactly matches the fish size and feeding habits.

ProPond® / NEO Index®

Feed your animals all year round with the natural, balanced JBL PROPOND fish food, and keep them healthy and active long-term. All the PROPOND products in this physiological-nutritional concept contain high-quality ingredients in accordance with the NEO Index®.

Outbreaks of disease after adding new fish

Pond enthusiasts sometimes notice that new fish cause an outbreak of disease, and thus assume that the retailer has sold them diseased pond fish. This is not usually the case! Again a comparison with humans serves to illustrate the problem. When the Spanish conquered South America in about 1500 AD, they introduced the “harmless” influenza virus. Since the natives of South America had never been exposed to influenza viruses before, they hadn’t enough resistance to them and died in their thousands. It can be similar in the pond. The newly added fish have harmless parasites, to which they have developed a resistance against. Your pond fish have never been in contact with these germs and are therefore very susceptible. So strengthening your fish’s immune system and also that of your new arrivals (the problem can go either way) with JBL AccliPond is highly recommended!

Outline of pond fish diseases

There are some diseases which occur again and again in pond fish and which can be quickly and reliably treated with special medications. There are only a few diseases where treatment is unfortunately not possible, as, is the case with the koi herpes virus. Here we will provide an outline of the most important pond fish diseases and explain whether or how you can treat them. The Online Hospital gives you the opportunity to diagnose fish diseases using pictures and to get tips for their treatment.


White spot disease (Ichthyo), scientific name: Ichthyophthirius multifiliis, also called Ichthyo or white spots.

This is a parasite from the group of the single-celled animals (Ciliates), which can be killed off quickly and safely with JBL MedoPond Plus *. This parasite has a life cycle with several stages during which it cannot be killed off. Only during a free floating "swarm out" phase is the successful elimination possible. That's why the treatment needs to be carried out over a period of two weeks at a water temperature of 25 °C. With cooler temperatures the treatment time is prolonged.

After the treatment is completed apply JBL AccliPond should be applied to aid the regeneration of the mucous membrane.

Fish leech (Hirudinea)

These leeches can be up to 5 cm long and attach themselves to the fish skin, suck blood and afterwards cause bacterial and fungal infections. You can’t combat leeches with over the counter medicines. Not even prescription medicines can kill off the leeches’ eggs. Manual removal of the leech is possible with pincers. Afterwards you need to add JBL Ektol bac Pond Plus * into the pond water to prevent likely bacterial secondary infections. Alternatively there is the option of bathing the fish for some minutes in a 2 to 3% sodium chloride (common salt) solution. The bath removes the leeches from the fish. A subsequent prophylaxis against bacterial infections is also advisable here.

Anchor worm = Lernaea crustaceans

Although this parasite, which can grow to about 20 mm long, is termed a „worm“, it belongs to the crustaceans. The juvenile stages of these parasites can survive for about 5 days without a host. JBL ArguPond Plus * makes a quick and safe treatment possible. Afterwards we recommend the application of an antibacterial remedy, such as JBL Ektol bac Pond Plus *, in order to prevent a bacterial infection of the “wound”. The infection with Lernaea crustaceans weakens the host fish and harbours the risk of a fungal or bacterial infection.

Carp louse (Argulus)

The carp louse Argulus is easily recognised on affected fish. It is a parasite. It can grow up to more than one centimetre long, and has a round, flattened body. The carp louse belongs to the fish lice (Branchiura) with about 70 crustacean species which live parasitically. They bore into the fish’s flesh to suck blood. Inflammations and infections can occur from the bite. If heavily infested, the fish will also lose weight. Treatment:

JBL ArguPond Plus * has been especially developed to combat carb lice and copepodes. Sodium chloride or potassium permanganate baths do not have any noticeable effect. Carp lice can also be removed from the fish using pincers. Afterwards an application of an antibacterial remedy, such as JBL Ektol bac Pond Plus * is advised, in order to prevent a bacterial infection of the “wound”.

Skin and gill flukes (Trematoda)

The pond fish’s most frequent worm diseases can quickly and effectively be combated with JBL ArguPond Plus *. Skin flukes (Gyrodactylus) can be seen by looking closely at the fish skin with the naked eye. Gill flukes (Dactylogyrus) can only be diagnosed reliably by means of a gill smear. For the egg laying gill flukes a second treatment is required.

Skin flukes
Gill flukes under the microscope

The active substance praziquantel helps for tapeworms (Cestoda), but in most countries it only is allowed to be prescribed by veterinarians. For this reason the JBL medication JBL GyroPond Plus (with praziquantel) is also not allowed to be sold in all countries.

Fungal infections (Achlya)

Fungal infections are easily recognisable on fish with their cotton wool-like formations. By adding JBL MedoPond Plus * fungal infections can quickly and reliably be combated. It is very important to start the treatment quickly because the fungus deposits poisonous metabolic products into the fish metabolism. This poisoning is the main problem. The fish can easily regenerate the destroyed fish skin and the surrounding tissue during the healing process. The visible fungal infection is often a secondary infection. The primary infection can be of a bacterial nature, or some such. In such cases a combined treatment is advised:

JBL Ektol bac Pond Plus * for the bacterial primary infection, complemented by JBL AccliPond which rebuilds and sustainably protects the destroyed mucous membrane of the fish.

Mouth and fin rot (Aeromonas, Pseudomonas)

This disease can be recognised by the fraying, rotting off and later by the complete loss of body parts. By adding JBL Ektol bac Pond Plus * the disease can be stopped quickly and the fish is able to completely regenerate the body parts affected. To build up sufficient energy reserves for the fish we recommend adding JBL Atvitol to the food twice a week. Mouth or fin rot is caused by water quality problems, even if the pathogen is of a bacterial nature. The causative bacteria of the Aeromonas and Pseudomonas group reproduce in the pond alarmingly quickly if the water quality is not right. Not only the right remedy but also an improvement of the water quality is necessary. The most important values, which need to be checked and if necessary corrected, are: carbonate hardness (KH), pH (pH value), ammonium (NH4)/ammonia (NH3) and nitrite (NO2). All you need to know about these water values and how to improve them can be found in the Online Hospital and in The water tests – all parameters .

Open wounds, ulcers etc.

Bacterial Infections: Internal and external bacterial infections can take on a wide variety of appearances, which can quickly and reliably be combated with JBL Ektol bac Pond Plus *. Whitish coatings often appear on the fish skin. However, bloodshot spots can also be discerned or completely different symptoms can occur. A clear diagnosis is only practically possible with a microscope. We often assume it is a parasitic infection, choose a suitable medicine, such as JBL MedoPond Plus * and if it doesn’t get better we use JBL Ektol bac Pond Plus *, which is effective against bacterial infections. This needs to be followed by JBL AccliPond which rebuilds and sustainably protects the destroyed mucous membrane of the fish.

Spring viraemia, SVC/virämia/Erythrodermatitis

This is a viral disease in fish (especially in carp-like fish like koi). The trigger is a virus by the name of Rhabdovirus carpio (RNA virus). This disease usually occurs in the spring in ponds with water temperatures between 10 to 20 °C. The symptoms are: bloodshot spots on the skin (at the edge of the fin), apathetic behaviour, sometimes pop-eyes and swollen abdominal cavities. Fish that survive the disease may remain carriers of the disease all their life without exhibiting symptoms themselves. Direct treatment with medication is not yet possible. It is important to improve the keeping conditions of the fish. The addition of vitamins in the food with JBL Atvitol is very helpful and might be combined with JBL AccliPond which rebuilds and sustainably protects the destroyed mucous membrane of the fish. Raising the temperature to above 20 °C has also been reported as helpful (Dr. Sandra Lechleiter: Krankheiten der Koi, DATZ aquarium books).

Ulcerous proliferations on the body, skin ulcers

The triggers for ulcers and open wounds on the body of the fish are bacteria, which are always to be found latent in the water or on the body of the fish. In a bad environment they can reproduce at great speed and cause problems. An antibacterial remedy such as JBL Ektol bac Pond Plus * is highly effective against the bacteria but not against the cause. It is essential that a cause study is carried out: water load, fish stock, planting, feeding and oxygen concentration need to be checked. In the garden pond it is noticeable that these problems always occur in spring. Increasing temperatures, combined with increasing fish activity and missing energy resources are the main reasons for the outbreak of the disease. The remedy and even more so the prevention are quite simple: As soon as the fish come out of hibernation and start to feed, they need the right low-temperature food ( Spring ). A weekly addition of JBL Atvitol provides the fish with strengthening vitamins to prevent an outbreak of the disease.

Koi herpes virus, KHV, koi pox

This often occurs in summer, even in the best fish keeping conditions, and is highly infectious. The pathogen is a virus which only reproduces above 10 and below 30 °C and which mostly affects only koi. The fish show massive mucous membrane changes and they die within a few days. In the gills you can detect a significant necrosis (fading and decay). The result is often that the fish stay near the water surface to gasp for “air”. Often you see their eyes are sunken. There is no really effective method of treatment. Any surviving fish are carriers of the virus and therefore infectious all their lives.

Popeyes (Exophthalmus)

One or both eyes stand out of the head oddly. The causes of this clearly visible disease can be varied. In most cases the cause is a deterioration of the water quality. An examination of pH, KH, ammonium, nitrite and nitrate is strongly advised. It has also been observed that vitamin deficiency in the nutrition can cause popeyes. Please check if a varied diet is being fed to the fish and whether opened food containers are being used up within 3 months at most. 3 months after opening the food tin there are hardly any vitamins present in the food. A subsequent adding of vitamins with JBL Atvitol is then required. If only a single fish is affected it can possibly be a bacterial infection. In this case the rapid use of JBL Ektol bac Pond Plus is required to combat the disease and to prevent its further spread. But it could also be the incurable fish tuberculosis.

Pop eyes on marine fish

* For information about risks and side-effects please read the pack insert and ask your veterinary surgeon or pharmacist.

Reduce risk of disease from the start with UV-C water clarifiers

A UV-C water clarifier not only ensures crystal clear water, but also reduces the bacterial count in the water. The amount of pathogenic germs is absolutely decisive for the risk of infection. If someone sneezes and coughs in your living room, the number of germs flying around is low and your risk of infection low. But if you are having a party with flu patients, it is almost guaranteed that you will also have flu the next day. With the help of a UV-C water clarifier it is possible to drastically reduce the amount of pathogenic germs in the water and thus effectively reduce the risk of infection for your pond fish. When using a UV-C water clarifier, it is always important to adjust the water flow rate to the strength of the UV-C water clarifier! If the pump output is too high, the water will flow past the germ-killing UV-C radiation too quickly without being sufficiently “sterilised." It is therefore essential that you adhere to the recommended pump outputs for their respective wattages:

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