Vibriosis in Fish

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 an immune-deficiency, Vibrio bacteria can be fatal to fish.

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, some species can infect freshwater fish.

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

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.

Symptoms of Vibriosis in Fish

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

Red Skin, Face, Fins, and Tail

Vibriosis can result in a fish developing skin ulcerations and hemorrhaging because of the liquifying of its internal organs which can show up as redness and ulcerations of the skin, face, fin, and tail. The results are redness throughout the body, fins, tail, eyes, and mouth.

Protruding Eyeballs and Corneal Opacity

A fish with some strains of the bacteria can have serious eye problems, beginning with protruding eyeballs and corneal lesions that cause an opacity over the eyes. The eyes will soon ulcerate and cause corneal lesions, characterized by an initial opacity, followed by ulceration, and then parts of the eye may dissolve.

Anorexia

A fish with the disease may stop eating and become listless, which slows down its growth and internal functioning.

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 if strict quarantine practices for new or sick fish are often ignored.

Immunocompromised fish, such as those stressed by poor water quality, bullying, or lack of sufficient nutrition, are more susceptible to bacterial infection. Traumatic wounds on a fish are also potential areas where there can be 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.

Diagnosing Vibrosis in Fish

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 cultures and sensitivity tests are critical.

Treatment

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. Treatments can include the following:

• Water: Test your water chemistry to make sure your levels are within normal range.
• Diet: Review the diet you are feeding your fish so they are not lacking essential nutrients and becoming immunocompromised.
• Stress reduction: Consider separating any aggressive tank mates. Secondary stress from bullying goes a long way in making Vibrio infections worse.
• Antibiotics: If caught early enough, medicines such as antibiotics can be given directly to the fish as an injection, formulated into a feed, or may require a water-based treatment.
  

Prognosis for Fish With Vibriosis

The prognosis for fish with vibriosis is poor. Many fish are never treated because they may not show any symptoms other than ulcers but die from the bacteria within a week or so of contracting the disease.

How to Prevent Vibriosis

To prevent a Vibrio outbreak in your aquarium, you must maintain a healthy and low-stress environment for your fish. The best methods of ensuring healthy fish include the following:

• Quarantining all new additions to your aquarium is critical to preventing vibriosis, just as it is to prevent other infectious diseases. This includes all fish, invertebrates, and live rock. You will need to keep them away from the main tank for at least four to six weeks, however, the bacteria may persist within the environment. Many fish systems likely harbor Vibrio bacteria that may never harm their inhabitants.
• Check the tank's water quality regularly and set a consistent maintenance routine.
• Maintain peace between your tank inhabitants and plan accordingly for new additions.
• Feed fish 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. 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. Eating contaminated raw shellfish, such as oysters, can also spread the bacteria from fish to humans (infections from eating raw fish are less common). Immunocompromised individuals are at risk for more serious symptoms.

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