Fish Tuberculosis

Fish species such as angelfish are particularly prone to contracting fish tuberculosis.

Fish tuberculosis is among the most common fish diseases. This is because the bacteria that cause fish tuberculosis are widespread and can be found in many aquariums. Discover when an outbreak might occur and what actions you should take.

How Dangerous is Fish Tuberculosis?
Symptoms and Progression: How Can I Recognise Fish Tuberculosis?
Diagnosis: How is Fish Tuberculosis Detected?
Treatment: What Can Be Done Against Fish Tuberculosis?
Causes: How Does Fish Tuberculosis Arise?
Prognosis: Is Fish Tuberculosis Curable?
Prevention: Can Fish Tuberculosis be Prevented?

How Dangerous is Fish Tuberculosis?

Caused by bacteria, fish tuberculosis is a frequent health problem in aquariums. In the worst cases, it can lead to the death of affected fish and therefore any suspicion of fish tuberculosis certainly warrants veterinary attention.

Which Fish Are Often Affected?

Nearly any ornamental fish can contract fish tuberculosis – whether they live in freshwater or saltwater. However, the disease often breaks out in fish with weakened immune systems. Guppies, tetras, and angelfish appear to be more commonly affected than, say, catfish.

Is Fish Tuberculosis Dangerous to Humans?

Fish tuberculosis can be transmitted to humans. It is also known as ‘Swimming Pool Granuloma’ and is characterized by painful and itchy skin rashes, especially on the hands and arms.

If you suspect an outbreak of fish tuberculosis in your aquarium, it’s best to protect yourself by avoiding direct contact with the infected water.

Wear gloves and never touch the water if you have open wounds. If you experience symptoms of the disease, seek medical advice from your GP.

Symptoms and Progression: How Can I Recognise Fish Tuberculosis?

Fish tuberculosis can develop slowly or spread rapidly. Depending on their immune status, infected fish may exhibit symptoms, but signs of illness do not always occur.

Based on clinical signs, it is usually not possible for aquarium owners to distinguish fish tuberculosis from other fish diseases. Therefore, consulting with a veterinarian is advisable.

The Acute Progression of Fish Tuberculosis

The acute progression of the disease is characterised by sudden inflammation and can advance within one to two weeks. The following symptoms may appear during this phase:

Lethargy and lack of appetite
A curved spine
Changes to the scales
Pale colour
Exophthalmos (bulging eyes)
Bloated abdomen

Additionally, affected fish develop white-grey nodules, known as granulomas, in almost all organs, but these are only visible after dissection.

The Chronic Progression

In most cases, fish tuberculosis progresses slowly, for example, in a chronic course: only a few fish occasionally develop nodules in their muscle tissue, visible from the outside as dark spots.

Eventually, these nodules burst open, releasing the bacteria into the water.

When Should I Visit the Vet?

As soon as you notice any signs of illness in your aquatic pets, you should scrutinise existing care and feeding conditions. Moreover, you should visit a veterinarian who is knowledgeable in fish diseases early on.

Timely treatment, such as for fish tuberculosis, can save lives or prevent other fish from infection.

Diagnosis: How is Fish Tuberculosis Detected?

To reliably identify fish tuberculosis, a vet typically performs a dissection on a deceased fish. Histological sections reveal the typical white-grey granulomas in the liver, spleen, and kidneys.

The vet can then conduct laboratory tests to directly confirm the presence of the pathogens.

However, the detection of bacteria without tissue changes is not a reliable indicator of a fish tuberculosis outbreak, as the bacteria can also naturally occur in fish.

Treatment: What Can Be Done Against Fish Tuberculosis?

Unfortunately, there is currently no cure for fish tuberculosis. However, with background knowledge on the disease and the right measures, you can slow its progression and protect healthy fish from becoming ill.

Measures Against New Infections

The most important method to prevent new infections is the isolation of sick fish. From now on, you should also avoid introducing new fish to this aquarium to allow the stock to naturally and gradually decline without infecting new inhabitants.

Do Fish with Fish Tuberculosis Have to be Euthanised?

Sometimes it may be necessary to have sick fish euthanised by a vet. By doing so, you spare your sick fish a painful death.

Causes: How Does Fish Tuberculosis Arise?

Fish tuberculosis is caused by bacteria of the Mycobacterium genus. These mycobacteria are estimated to be present in up to 80 percent of all aquariums and adhere to the external mucous layer of the fish. They naturally occur in the substrate or on other materials in the aquarium as well.

The Immune System Plays a Crucial Role

While healthy fish are protected from the bacteria by their intact mucous membrane, this protective mechanism is lacking in sick animals. In immunocompromised fish, the mucous membrane is disrupted, allowing the bacteria to multiply rapidly.

Note: Immune weakness is often the result of poor care or feeding – for example, if your fish do not receive enough nutrients, such as vitamins.

Stress Triggers the Onset of the Disease

Fish tuberculosis often occurs when fish are under stress. Stress can arise, for instance, during pecking order battles.

Other triggers could be the introduction of new fish to the aquarium or incorrect water parameters such as high temperatures.

Is Fish Tuberculosis Contagious to Other Fish?

Fish tuberculosis is highly contagious. Transmission occurs not only from fish to fish but also through indirect contact, such as via contaminated substrate.

For this reason, fish tuberculosis can spread like an epidemic, quickly leading to the entire stock’s death.

aquarium temperature being checked with thermometer. — The water quality in an aquarium greatly affects the health of fish and should be checked regularly.

Prognosis: Is Fish Tuberculosis Curable?

As of the current date (08/2024), there is no medication for fish tuberculosis that leads to a cure. Thus, an outbreak of the disease generally results in death, depending on its form.

How Long Can Mycobacteria Survive in an Aquarium?

Mycobacteria can survive for an extended period in an aquarium, which is why the disease often recurs. The bacteria firmly attach to substrates, aquarium plants, or furnishings.

Note: After the loss of your sick stock, you should disinfect and thoroughly clean the aquarium if you wish to reuse it. This includes all associated items. The substrate and plants should ideally be completely renewed.

Prevention: Can Fish Tuberculosis be Prevented?

Proper prevention is the best way to protect fish from fish tuberculosis. Providing species-appropriate husbandry and feeding, you can ensure a strong immune system in your fish, helping them withstand mycobacteria for an extended period.

Regularly observing your fish for any changes and checking the water quality can help combat infectious diseases like fish tuberculosis.

When Introducing New Fish Into the Aquarium

New fish are potential carriers of pathogens. Therefore, it is essential to keep newcomers isolated in a separate quarantine tank for at least two to three weeks.

Only if they still appear healthy and active after this time should you integrate them into your stock.

set of fish in plastic bags being quarantined — You should initially keep any new additions to your aquarium in quarantine to prevent the spread of fish tuberculosis.

This article from zooplus Magazine is purely informative. If your pet is experiencing discomfort, contact your veterinarian for diagnosis and treatment.

Franziska G., Veterinarian

At the Justus-Liebig-University of Giessen I was extensively trained as a veterinarian and was able to gain experience in various fields such as small animal, large animal and exotic animal medicine as well as pharmacology, pathology and food hygiene. Since then, I have been working not only as a veterinary author, but also on my scientifically driven dissertation. My goal is to better protect animals from pathogenic bacterial organisms in the future. Besides my veterinary knowledge, I also share my own experiences as a happy dog owner and can thus understand and enlighten fears and problems as well as other important questions about animal health.

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