Bacterial Diseases of Fish (Freshwater & Saltwater)

Bacterial diseases of fish are caused by bacteria and can result in serious illness and even death in fish.

There are many different types of bacteria that can cause disease in fish, and some of the most common bacterial diseases include strep throat, tuberculosis, and cholera.

These diseases can cause a wide variety of symptoms in fish, including lethargy, loss of appetite, bloating, skin lesions, and fin rot. In severe cases, bacterial diseases can lead to coma or death.

There are a number of ways to prevent bacterial diseases in fish. The most important step is to maintain good water quality by regularly testing and monitoring the water parameters and making adjustments as necessary.

You can also help prevent disease by providing a clean environment for your fish and feeding them a healthy diet.

Bacterial Diseases of Fish

Here is the list of fish bacterial diseases with their causative agents;

Disease NameDisease Causing Bacteria
VibriosisVibrio anguillarum, Vibrio ordalii
FurunculosisAeromonas salmonlcida
Motile Aeromonas septicemiaAeromonas hydrophila
Bacterial haemorrhagic or Pseudomonas septicemiaPseudomonas
EdwardsiellosisEdwardsiella tarda
Enteric red mouthYersinia ruckeri
ColumnarisFlexibacter columnaris
Low temperature or coldwater diseaseCytophaga psychrophila
Bacterial gill diseaseCytophagal or Flavobacterial organisms
Fin rotCytophagal or other bacteria
Salt water columnarisSporocytophaga
Bacterial kidney diseaseRenibacterium salmoninarum
Pseudo kidney diseaseLactobacillus
Streptococcal septicemiaStreptococcus
Eubacterial meningitisEubacterium tarentellus


Vibriosis is a bacterial infection that can affect both fresh and saltwater fish. Vibriosis due to Vibrio anguillarum and Vibrio ordalli primarily affect fish in salt water.

The bacteria are typically found in contaminated water, and can cause a number of serious health problems in fish, including skin lesions, organ damage, and death.

Vibriosis is particularly concerning in commercial fisheries, as the infection can spread quickly through a population of fish and lead to significant financial losses.

Infected fish may exhibit a variety of symptoms, including lethargy, loss of appetite, and increased mucus production. In severe cases, vibriosis can be fatal.

While there is no cure for vibriosis, affected fish can be treated with antibiotics. However, the best way to prevent the disease is to maintain clean and healthy water conditions in aquaculture facilities.

Control of this disease is relevant for the rearing of salmonids and other species in brackish or salt water.


Edwardsiellosis in fish is a serious disease that can have a devastating impact on fish populations. The disease is caused by the bacterium Edwardsiella tarda, which is found in fresh and salt water environments.

Infected fish typically exhibit symptoms such as lethargy, anorexia, and ulcerative lesions. In severe cases, edwardsiellosis can lead to death.

Edwardsiellosis is of particular concern in aquaculture operations, where it can cause significant economic losses.

Prevention is the best method of control, and measures such as good water quality management and biosecurity are essential for preventing the spread of edwardsiellosis in fish populations.

Motile Aeromonas Septicemia

Motile Aeromonas septicemia is a bacterial infection of fish that is caused by the bacterium Aeromonas hydrophila. Motile Aeromonas septicemia can affect both fresh and salt water fish, and has been reported in a wide variety of fish species.

This disease is often fatal to fish, and can cause significant losses in aquaculture operations.

Clinical signs of this disease include lethargy, anorexia, excreting white feces, and increased body surface mucus production.

In advanced stages of the disease, fish may exhibit hemorrhagic lesions on their skin and fins.

Treatment of motile aeromonas septicemia is difficult, and often unsuccessful. Prevention of this disease through good aquaculture husbandry practices is the best method of control.


Columnaris in fish is a common infection that can be fatal if left untreated. Columnaris is caused by the bacterium Flavobacterium columnare and is often referred to as “cotton mouth” or “slimy mouth”.

Symptoms of columnaris include white or gray patches on the skin, fins, and mouth. The infection can also cause ulcers, tissue necrosis, and fin rot.

Columnaris is often spread through contaminated water or food, and it can be difficult to treat once it has become established in a fish population. Early diagnosis and treatment are crucial to preventing the spread of this disease.

Columnaris is a common ailment in fish that can be easily treated if caught early. The symptoms of columnaris include: white patches on the skin, fraying fins, and increased mucus production.

If left untreated, columnaris can lead to death. The good news is that columnaris is relatively easy to treat with antibiotics. If you suspect your fish has columnaris, take them to the vet for a diagnosis and treatment plan.

Bacterial Gill Disease

Bacterial gill disease in fish is a common ailment that can be caused by either Cytophagal or Flavobacterial organisms. These diseases can cause serious respiratory distress in fish and often lead to death.

Bacterial gill disease in fish is a serious problem that can lead to death. The bacteria cause inflammation and damage to the gills, making it difficult for the fish to breathe.

Early diagnosis and treatment is essential for the successful treatment of bacterial gill disease in fish.

Treatment of bacterial gill disease in fish is important to prevent this from happening. There are several products on the market that can be used to treat this disease, but it is important to choose the right one for your fish.

Fin Rot

Fin rot in fish is a serious problem that can lead to death. It is caused by a bacteria that infects the tissue of the fins, causing them to rot. Fin rot in fish is a serious problem caused by Cytophagal or other bacteria.

The bacteria are usually present in the water, and can be transmitted to the fish through open wounds or breaks in the skin. Fin rot can also be caused by poor water quality, which allows the bacteria to multiply.

Treatment for fin rot includes adding salt to the water and removing any dead or dying tissue from the affected fish.

Symptoms of fin rot include fraying or disintegration of the fins, redness or inflammation of the skin, and ulcerations. The disease progresses rapidly and can quickly lead to death if not treated.

Treatment involves removal of the infected tissue and administration of antibiotics. Prevention of fin rot includes maintaining clean water conditions and quarantine of new fish.

Enteric Red Mouth

Enteric red mouth is a condition that results in discoloration of the inside of a fish’s mouth. The condition is caused by a build-up of bacteria on the gills and in the intestines.

This can cause the fish to have difficulty breathing and eating. In extreme cases, the fish may die. Enteric red mouth is most often seen in freshwater fish, but it can also occur in saltwater fish.

There are several things that can be done to prevent enteric red mouth, including keeping the aquarium clean and maintaining proper water quality.

Enteric red mouth in fish is a bacterial infection that affects the fish’s gastrointestinal tract. The bacteria that cause this infection are called Yersinia ruckeri. This bacteria is found in fresh water, and can be transmitted to fish through contaminated water.

Symptoms of enteric red mouth in fish include red lesions on the mouth and gills, loss of appetite, lethargy, and increased mucus production. This disease can be deadly to fish, and often leads to death within two weeks.

Treatment for enteric red mouth in fish is typically not effective, and the best way to prevent this disease is to maintain clean water conditions.