Bacterial skin infection in whelks

What is it?

The whelk (Buccinum undatum) is a large marine snail living on sandy or muddy seabeds, highly valued in fishing and farming for its meat. Like other marine mollusks, it can be affected by bacterial infections affecting its mantle, muscular foot, or shell. These infections occur mainly in farmed conditions or storage tanks when animals are kept at high stocking densities or in poor water quality. The disease manifests as localized lesions on the soft body parts, sometimes accompanied by shell erosion. It remains poorly characterized scientifically in this species, unlike other mollusks such as oysters or abalones, which have been more extensively studied.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

Several genera of opportunistic marine bacteria may be involved, notably Vibrio and other bacteria naturally present in seawater. These bacteria take advantage of animal weakness or injury to the shell or foot in order to establish and multiply, leading to localized infection that may then spread.

High animal stocking density in rearing tanks or cages promotes disease spread between individuals. Poor water quality, elevated temperature, stress from transport or handling, and mechanical damage to the shell (handling, sorting, transport) increase infection risk. General weakness in the animal, for example following a prolonged fasting period, also plays a contributing role.

Transmission

Transmission occurs mainly through water, between individuals kept in close quarters in the same tank or storage facility, promoted by direct contact and poor water quality.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

Individual treatment is rarely practical in real-world situations. In rearing systems, management focuses primarily on improving environmental conditions (water quality, stocking density, temperature) rather than direct medical treatment of the animals. The use of antibacterial agents is not a common practice and is not recommended for this species intended for human consumption.

Prevention

Possible complications

An uncontrolled infection can spread to other parts of the animal's body and result in death. In a rearing facility, it can spread to other individuals in the same tank, causing economic losses through mortality.

When to see a veterinarian

Prognosis

The prognosis depends on how quickly husbandry conditions are corrected and the extent of the infection. Early management of stress factors often helps limit spread of the disease. Without intervention, the outcome may be unfavorable for severely affected individuals.

Frequently asked questions

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

Content reviewed by the TunisieVet editorial team · Updated 30 August 2026