Vibriosis in Fish

Saltwater fish tank

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Vibriosis is caused by a common tank bacteria. Most of the time, these bacteria do not cause any issues for your fish and exist in the detritus or debris in the aquarium substrate. However, if the fish’s defenses are lowered due to stress or immune-deficiency, Vibrio bacteria can cause life-threatening disease.

There are known Vibrio species that are more virulent and will cause more severe outbreaks than other species. Vibriosis is a zoonotic disease and can infect humans, sometimes with very serious consequences.

What is Vibriosis?

Vibriosis is the disease caused by gram-negative, facultative anaerobic rod bacteria from the Vibrio genus. There are many strains of Vibrio present in the aquatic environment at all times. Although they are more common in marine systems, there are species that can infect freshwater fish.

Some strains are more pathogenic than others and will spread disease more readily, especially if fish are compromised due to immune dysfunction.

This disease can occur in both pet fish and aquaculture food fish species. It is not common in pet fish and scientists have developed effective vaccines for aquacultured fish species.

Symptoms of Vibriosis in Fish

There are many signs of Vibriosis that may be seen. These symptoms are not pathognomonic (specific to Vibrio bacteria) and may be caused by other diseases.


  • Red fins
  • Red mouth, operculum and eyes
  • Exophthalmia and corneal opacity
  • Anorexia
  • Pale gills
  • Sudden death

Causes of Vibriosis

Vibriosis is caused by an infection of Vibrio bacteria species. There are many bacteria present at all times within the aquatic environment. More severe Vibrio strains may enter a fish system that ignores strict quarantine practices. Immune-compromised fish, such as those stressed by poor water qualitybullying or lack of sufficient nutrition, are more susceptible to bacterial infection. Traumatic wounds are also potential areas of increased bacteria growth.

Vibrio bacteria are known to be more problematic in warmer temperatures. If your aquarium or pond fluctuates in water temperature, you may see more clinical signs when the water is warmer compared to colder water temperatures.

Diagnostic Process

In a suspected Vibriosis outbreak, your veterinarian will collect recently deceased fish or moribund fish close to death to be submitted to a specific laboratory. The laboratory will perform bacterial culture and antibiotic sensitivity testing to identify the prominent bacteria present and which antibiotic it is most susceptible to. There are known bacterial resistances to antibiotics, so the culture and sensitivity testing is critical.

In most cases, you will need to identify and correct any potential stressors in your aquarium. This may include improving maintenance, feeding a better diet, more balanced water conditions or removing aggressive fish.


If you suspect your fish is infected with Vibriosis, move them to a hospital or quarantine tank. Test your water chemistry to make sure your levels are within normal range, evaluate your fish's diet, and consider separating any aggressive tank mates. Secondary stress goes a long way in making Vibrio infections worse.

Over-the-counter "antibiotics" are not effective against Vibriosis. There are many known resistant strains of Vibrio that require the correct treatment. Once a diagnostic culture and sensitivity test has been performed, your veterinarian will determine the best course of action. Antibiotics can be given directly to the fish as an injection, formulated into a feed, or may require a water-based treatment.

How to Prevent Vibriosis

As with other infectious diseases, quarantining all new additions to your aquarium is critical. This includes all fish, invertebrates, and live rock. You will need to keep them away for at least four weeks, however, the bacteria may still persist within the environment. Many fish systems likely harbor Vibrio bacteria that may never harm their inhabitants.

In order to prevent a Vibrio outbreak in your aquarium, it is critical that you maintain a healthy and low-stress environment for your fish. The best methods of ensuring healthy fish include the following:

  • Quarantine all new live additions for at least four to six weeks (includes plants, invertebrates and live rock)
  • Check your water quality regularly and set a consistent maintenance routine
  • Maintain peace between your tank inhabitants and plan accordingly for new additions
  • Feed a high-quality diet and be sure to consider the appetites of all your fish
  • Routinely check all your fish for any signs of disease and call your aquatic veterinarian with any concerns as soon as possible

Is Vibriosis Contagious to Humans?

Vibriosis is a known zoonotic disease and is contagious to humans. Bacteria can enter through cuts and scrapes on the skin, causing a localized infection and inflammation. Immune-compromised individuals are at risk for more serious symptoms.

Certain strains of Vibrio are known as "flesh-eating bacteria," and can cause life-threatening infections resulting in amputations if not treated early enough. Be sure to always wash your hands using soap after cleaning an aquarium or handling fish.