Bacterial infection in lobsters (Vibrio and Aeromonas)
Bacterial infection in European lobsters (Homarus gammarus) is a disease caused mainly by bacteria of the genera Vibrio and Aeromonas, which occur naturally in seawater. These bacteria often take advantage of shell damage or significant st...
What is it?
Bacterial infection in European lobsters (Homarus gammarus) is a disease caused mainly by bacteria of the genera Vibrio and Aeromonas, which occur naturally in seawater.
These bacteria often take advantage of shell damage or significant stress in the lobster to develop and cause infection, sometimes spreading throughout the entire body.
This disease mainly affects lobsters raised in tanks, holding systems, or transported in poor conditions, but can also occur in the wild.
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:
Signs are often subtle at first and may go unnoticed.
The lobster may appear abnormally soft or unresponsive, remaining motionless in a corner of the tank.
Dark patches, lesions, or small wounds on the shell may appear, sometimes accompanied by an unusual odour.
In more advanced cases, the lobster may stop feeding, show disorganised swimming or abnormal movements of the legs and antennae, and eventually die with no obvious external signs.
The haemolymph (the lobster's "blood") may become cloudy instead of clear, which is a sign observed by professionals during handling.
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 the proliferation of opportunistic bacteria, mainly Vibrio spp. and Aeromonas spp., which occur naturally in seawater and sediments.
These bacteria become pathogenic when the lobster is weakened: shell injury, handling stress, poor water quality, or overcrowding in holding tanks.
The main risk factors are shell damage (scratches, recent molting, bites from fighting), poor water quality (excessive temperature, lack of oxygen, organic matter buildup), stress from transport or handling, and overcrowding in holding tanks.
Lobsters that have recently molted, with still-soft shells, are especially vulnerable.
Transmission
Transmission occurs mainly through contaminated water, which naturally contains these bacteria and allows them to enter via shell damage or a weakened area. Overcrowding in a tank can promote spread if water is not properly circulated.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is difficult to make on your own because signs are nonspecific.
A veterinarian specializing in aquatic animals or a crustacean pathologist can confirm infection through hemolymph sampling and laboratory bacterial analysis, making it possible to identify the causative bacterium or bacteria.
Additional testing on tissues or shell may also be performed if visible lesions are present.
Treatment
Management relies mainly on improving farming conditions: water quality, stress reduction, and isolation of affected animals.
In a professional setting supervised by a veterinarian or specialist, targeted antibacterial treatment may be considered, but use must remain exceptional and controlled, particularly to limit the development of bacterial resistance in the aquatic environment.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention depends mainly on good farming or storage management: clean, well-oxygenated water, appropriate temperature, reasonable density in tanks, and gentle handling to avoid injury.
It is recommended to separate injured or recently molted lobsters from others, disinfect equipment and tanks regularly, and minimize stress during transport as much as possible.
Regular monitoring of shell condition and lobster behavior allows problems to be detected early.
Possible complications
Without treatment, infection can progress to generalized septicemia (systemic infection) which is often fatal.
The disease may also promote other secondary infections and lead to significant losses in storage or farming tanks due to animal proximity.
When to see a veterinarian
Lobster abnormally soft, lethargic, or immobile in the tank
Presence of spots, lesions, or unusual odor on the shell
Loss of appetite or abnormal behavior
Unexplained deaths in a group of lobsters held together
Turbid hemolymph observed during professional handling
Prognosis
The outlook depends on the stage at which the infection is detected. When caught early and with improved living conditions, a lobster can recover.
If the infection becomes systemic with involvement of the hemolymph, the outlook becomes guarded to poor, with mortality potentially occurring rapidly.
Frequently asked questions
Can this disease be transmitted to humans?
Vibrio and Aeromonas bacteria can exist in the marine environment and affect other species, but lobster infection in itself is not considered a classical zoonosis. Good hygiene remains recommended when handling sick animals.
Can you treat a sick lobster yourself?
No, it is not recommended to use antibiotics without professional advice. The best immediate action is to isolate the suspect animal and improve water quality, then contact a specialist.
How can you prevent an entire tank of lobsters from becoming contaminated?
By quickly isolating any individual showing abnormal signs, maintaining clean and well-oxygenated water, and avoiding overstocking in the tanks.
Is a lobster that has just molted more at risk?
Yes, just after molting, its shell is soft and much less protective, which makes it easier for bacteria to enter. Increased monitoring is useful during this period.
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 27 August 2026
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