Bacterial skin infection in hake
Bacterial skin infection in hake is a skin condition caused by opportunistic bacteria that occur naturally in seawater. This fish, called Merluccius merluccius, lives mainly in the wild but can also be kept in tanks or captured and handled...
What is it?
Bacterial skin infection in hake is a skin condition caused by opportunistic bacteria that occur naturally in seawater. This fish, called Merluccius merluccius, lives mainly in the wild but can also be kept in tanks or captured and handled during research or experimental farming. The infection typically develops when the fish's skin is compromised by a wound, stress, or poor water quality. It appears as visible lesions on the body that can worsen rapidly without treatment.
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:
Early signs are often subtle: the fish swims less smoothly, appears tired, or keeps apart from others. Red or discoloured patches appear on the skin and may progress to open wounds, crusts, or ulcers. The fins may appear damaged or frayed. The hake may rub against the tank walls or bottom, a sign of irritation. Loss of appetite and general lethargy often accompany more advanced cases. In severe forms, lesions can spread and lead to a more widespread infection.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Various opportunistic marine bacteria, notably certain species of the genus Vibrio or Pseudomonas, can colonize the hake's skin when it is damaged. These bacteria take advantage of any break in the skin barrier—whether from trauma, parasites, handling, or significant stress—to multiply and cause a local infection.
Stress from capture, transport, or handling weakens the fish's natural defences. Poor water quality with high organic load or low oxygen levels promotes bacterial growth. Mechanical injuries—for instance from contact with nets, rough surfaces, or other fish—open the way to infection. Overcrowding in tanks and sudden changes in temperature or salinity are also aggravating factors.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis relies on careful observation of skin lesions by a veterinarian specializing in fish pathology or an aquaculture specialist. A skin or tissue sample from the affected area can be analyzed in the laboratory to identify the causative bacterium and guide the most appropriate treatment.
Treatment
Management may include antibacterial treatments suited to the species and marine environment, as well as local care to clean and protect the lesions. Improving farming conditions, particularly water quality, is an integral part of treatment. Any therapeutic decision must be overseen by a professional with expertise in aquaculture pathology.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention focuses primarily on maintaining good water quality and handling fish gently. Minimizing stress during capture or transport, avoiding overcrowding in tanks, and regularly monitoring skin condition help reduce risk. Proper disinfection of equipment and surfaces in contact with fish also helps limit the bacterial load in the environment.
Possible complications
Without treatment, skin infection can spread deeper into underlying tissues. It may also trigger a generalized infection affecting other organs, which significantly worsens the prognosis. Weakened fish become increasingly vulnerable to other pathogens.
When to see a veterinarian
Appearance of unusual lesions, wounds, or crusts on the skin.
Abnormal swimming, lethargy, or isolation from the rest of the group.
Persistent loss of appetite.
Damaged or frayed fins without obvious traumatic cause.
Prognosis
The prognosis is favorable if infection is detected early and environmental conditions are corrected quickly. However, delayed treatment or extensive infection may compromise the fish's survival.
Frequently asked questions
Can this infection be transmitted to humans?
No, this is not a known zoonotic disease. It remains specific to fish and poses no direct risk to humans.
Can hake heal from this infection on its own?
A very mild lesion can sometimes heal on its own if the water is of good quality, but an established infection generally requires intervention to prevent it from worsening.
How can I tell if my pool is prone to this type of infection?
Cloudy water, poor oxygenation, or high fish density increases the risk. Regular monitoring of water parameters is recommended.
Should you isolate an affected hake?
Yes, isolating the affected fish helps minimize additional stress and facilitates monitoring, while reducing the risk of bacterial spread in the tank.
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 23 August 2026
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