Furunculosis in catfish
Furunculosis is a bacterial disease affecting many freshwater fish, including catfish (Silurus glanis). It is caused by bacteria of the genus Aeromonas, often Aeromonas salmonicida or closely related species. The disease causes furuncles—ab...
What is it?
Furunculosis is a bacterial disease affecting many freshwater fish, including catfish (Silurus glanis). It is caused by bacteria of the genus Aeromonas, often Aeromonas salmonicida or closely related species. The disease causes furuncles—abscesses beneath the skin—which can progress to open wounds. This condition is particularly known in fish farming and can cause significant losses in affected populations if not treated promptly.
Key point
This disease can cause significant mortality in farmed populations if not detected and treated promptly.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Infected catfish develop swellings under the skin, sometimes visible as firm lumps that may later open into sores. These lesions can appear on the body, head, or near the fins. Fish often become less active, refuse to eat, and may swim abnormally, near the surface or on their side. Belly swelling linked to internal infection is sometimes observed. In severe cases, rapid death may occur without prior visible signs, especially in young catfish.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease results from bacterial infection, mainly by bacteria of the genus Aeromonas. These bacteria occur naturally in water and become pathogenic when the fish is weakened or stressed. Infection develops through skin wounds, stress from transport or handling, overstocking, or poor water quality.
The main risk factors are poor water quality (low oxygen levels, high temperature, organic matter buildup), overcrowding of fish, repeated stress (transport, handling, abrupt environmental changes), and pre-existing skin wounds. Catfish weakened by other diseases or poor nutrition are more susceptible. Rapid fluctuations in water temperature also promote disease development.
Transmission
The bacteria spread chiefly through contaminated water, by direct contact between fish, or via non-disinfected farming equipment. Introduction by an asymptomatic carrier fish is also possible.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is based on observation of typical skin lesions combined with laboratory analysis by a veterinarian. Sampling from lesions or affected fish allows isolation and identification of the responsible bacterium. Water analysis from the pond or tank is often performed at the same time to identify contributing factors.
Treatment
Treatment uses appropriate antibiotics, prescribed only by a veterinarian specializing in fish disease, typically given through feed or as medicated baths. Improving water quality and reducing stress are essential measures that accompany treatment. In some cases, isolating affected fish helps limit spread.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention centers on maintaining good water quality: adequate oxygen levels, appropriate filtration, and regular monitoring of water parameters. It is important to avoid overstocking in ponds or tanks and to limit stressful handling of fish. Quarantine of any new fish introduced to a farm or pond helps reduce the risk of bacterial introduction. Balanced feeding strengthens the natural resistance of fish.
Possible complications
Without treatment, the disease can progress to deep lesions affecting muscle tissue, or even generalized infection leading to death. In farmed populations, failure to control the disease can result in significant losses affecting a large proportion of the population.
When to see a veterinarian
Appearance of lumps or unusual wounds on the catfish's skin.
Decreased appetite or behavior change in one or more fish.
Abnormal swimming, lethargy, or a fish withdrawing from the group.
Unexplained deaths in a pond or tank.
Prognosis
The outlook depends on how quickly treatment is started. Early detection combined with improved farming conditions and appropriate treatment usually leads to good recovery. Without treatment, the condition may worsen, especially in young catfish or when farming conditions are poor.
Frequently asked questions
Is catfish furunculosis contagious to other fish in the pond?
Yes, the bacterium responsible can spread through water and affect other fish, especially if environmental conditions are unfavorable.
Can you eat a catfish that has had furunculosis?
It is recommended to consult a veterinarian before consumption, especially if the fish has been treated with antibiotics, in order to comply with safety withdrawal periods.
Does this disease affect only catfish?
No, furunculosis can affect many freshwater fish species, particularly in fish farming.
How can I tell if my pond water is promoting this disease?
Regular monitoring of water parameters (oxygen, temperature, ammonia) by a professional makes it possible to identify risk factors before symptoms appear.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 22 August 2026
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