Bacterial skin infection in turbot
Bacterial skin infection in turbot encompasses several skin diseases caused by opportunistic or pathogenic bacteria present in seawater or farming tanks. It mainly affects turbot raised in intensive aquaculture, in tanks or cages. The bacte...
What is it?
Bacterial skin infection in turbot encompasses several skin diseases caused by opportunistic or pathogenic bacteria present in seawater or farming tanks. It mainly affects turbot raised in intensive aquaculture, in tanks or cages. The bacteria most often involved belong to the genera Vibrio, Aeromonas, Pseudomonas, or Tenacibaculum. This disease is a major concern for aquaculture farms because it can cause significant economic losses 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:
Affected fish display visible skin lesions: redness, small wounds, ulcers, or areas where scales and skin are sloughing off. These lesions often appear on the flanks, head, or near the fins. The skin may appear opaque or discolored around the wounds.
Sick turbot swim abnormally, sometimes at the surface or in a disorderly manner. The fish may rub against the tank walls or bottom, as if relieving itching or discomfort.
A decrease in appetite is often seen, along with lethargy, and the fish may remain motionless at the bottom of the tank. In advanced cases, the belly may appear swollen and internal complications may develop.
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 is caused by bacteria naturally present in the marine aquatic environment, which become pathogenic when the fish is weakened or its skin is damaged. The bacterial genera most frequently identified are Vibrio (notably Vibrio anguillarum and Vibrio splendidus), Tenacibaculum maritimum (responsible for tenacibaculosis), Aeromonas salmonicida, and Pseudomonas. These bacteria enter through a wound, skin abrasion, or through the gills, then multiply in the skin and sometimes in deeper tissues.
Poor water quality, overstocking of fish in tanks, sudden changes in temperature or salinity, stress from transport or handling, and skin wounds caused by farming equipment or fighting between fish promote the onset of disease. A weakened immune system due to inadequate diet or another infection also increases risk.
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 clinical observation of skin lesions by a veterinarian or specialized aquaculture technician, supported by collection of lesion samples for bacterial identification in the laboratory. This analysis determines which bacterial species is responsible and allows selection of the most appropriate treatment.
Treatment
Treatment involves the use of antibiotics targeted to the identified bacterium, usually given orally through medicated feed or by bath immersion, according to the aquaculture veterinarian's recommendations. Local wound care and improvement of farming conditions accompany the antibiotic treatment.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention relies primarily on good farming practices: maintaining optimal water quality, avoiding excessive stocking densities, limiting stressful handling, and regularly disinfecting equipment and tanks. Vaccination against certain bacteria such as Vibrio anguillarum is available and can be used preventively in some farms. Regular monitoring allows early detection of the first signs and isolation of affected fish to prevent spread.
Vaccination
Vaccines are available against certain bacteria responsible for the disease, particularly Vibrio anguillarum, and are sometimes used preventively in intensive turbot farms, especially when introducing juvenile fish.
Possible complications
Without treatment, the infection can spread deeper and cause generalized septicemia, often fatal. Open skin lesions also favour secondary infections by fungi or other bacteria. Significant mortality can occur in the tank within a few days if the disease is not controlled.
When to see a veterinarian
Appearance of skin lesions, redness or ulcers on one or more fish in the tank
Abnormal swimming behaviour or fish rubbing against the walls
Loss of appetite or unusual lethargy in several individuals
Unexplained mortality or increasing mortality in the tank
Prognosis
The outlook is good if the disease is caught early and treated promptly with appropriate antibiotics and improved farming conditions. However, if the infection progresses to septicemia or spreads to large numbers of fish, the outlook becomes guarded and economic losses can be substantial.
Frequently asked questions
Can this disease be transmitted to humans?
No, the bacteria responsible for this skin infection in turbot are not considered transmissible to humans under normal handling or consumption conditions.
How to know if my turbot farming is affected?
The appearance of skin lesions, abnormal swimming behavior, or unusual mortality should raise concern. Only laboratory analysis of a sample can confirm the bacterium responsible.
Can this disease be prevented without a vaccine?
Yes, good water quality management, reasonable stocking density, and stress reduction significantly lower the risk of disease occurrence.
Can the affected fish heal completely?
With appropriate and prompt antibiotic treatment, as well as improved husbandry conditions, recovery is possible, especially if the lesions are still superficial.
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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