What Causes Tuberculosis in Fish?

What Causes Tuberculosis in Fish?

Here are the main causes of Tuberculosis in fish, we have also added the signs, symptoms, and methods to treat it.

What Causes Tuberculosis in Fish? Tuberculosis in fish is a contagious disease that can occur in aquarium fish and is caused by Mycobacterium Marium. You can diagnose Fish TB by observing signs and symptoms such as multiple granulomas in visceral organs, wasting, ulcers, greyish-white nodules, and dropsy eyes. All these help you to know that your fish has tuberculosis. 

Fish TB shows up some typical signs and symptoms in the body, and it requires special care and treatment; it is a significant zoonotic disease. Nearly all fish can develop fish TB, but some species are more vulnerable to TB.

What Causes Tuberculosis in Fish?

Fish are also susceptible to many diseases like other living organisms, and one common condition is fish tuberculosis. 

The bacteria can live in water and can contaminate live food, so when fish ingest these contaminated live food, they catch the bacteria. Sometimes, the infected fish may live up to many years without showing symptoms that make it hard for the owner to diagnose it.

Mycobacterium Marium is the causative agent of TB in both fish and humans. It is acid-fast rod-shaped bacteria and does not stain by traditional means. It swims freely in the fresh and saltwater and mostly present at the bottom of ponds or lakes.

It is quite resistant as it has a unique outer coating that protects it from many drugs and medications. It is always present in the bio-films of the tank. The infection can be acute or chronic and usually effect immune-compromised fish.  

Some strains are too virulent, but M. Marium is less virulent and usually can grow at 37 degrees Celsius temperature. The ideal temperature for this bacteria’s growth is 25-35 degrees Celsius, and it does not grow in low temperatures.

Other pathogens of Mycobacterium species that infect fish are M. Foruitm, M. Peregrinum, M. Ulcerans, M. Flavescens, M. Gordonae, and many more. All these strains infect both aquarium fish and humans.

Symptoms of Fish TB

Not all fish show symptoms as some fish remain asymptomatic throughout life but mostly show them. The main symptoms to identify TB is granulomas or white nodules on the internal organs of fish. Some of these granulomas break in the blood vessel and spreads disease in the whole body.

Other symptoms include:

  • Lethargy
  • Anorexia
  • Emaciation
  • Frank ulcers on the skin
  • Hemorrhage or hyperemia around the head
  • Loss of scales
  • The pallor of the skin and gills
  • Wasting
  • Lesions on the body
  • Discoloration of scales
  • Dropsy
  • Bulging eyes
  • Abnormal behavior
  • Loss of appetite
  • Listlessness
  • Bloating/swelling
  • Spinal deformities
  • Sluggish movement
  • Fin rot
  • Fluid accumulation
  • Abdominal distension
  • Reproductive problems 

How to diagnose Fish TB?

Diagnostic testing identifies and confirms the presence of TB bacteria. An examination of granulomatous lesions through a microscope helps detect the bacteria because it is present in the middle.

Histological sections or tissue imprints from the fish body also reveals the presence of acid-fast bacilli. PCR tests also help detect the causative agent, but these tests do not provide information on disease stage or severity. Immunocytochemistry is another tool that supports the diagnosis of bacteria.

How does the TB infection begin in fish?

It usually transmits from contaminated water, excessive crowding, carrier fish, infected plants or live commercial feed, through cuts or bruises, and from the owner’s hand if he has TB.

Snails and parasites also transmit the disease. The bacteria also spreads when a healthy fish eat wastes, scraps, and feces of the infected animal.

It usually begins from the mouth when the fish eat infected dead prey or live contaminated food. After entering into the mouth, it invades the body and activates inflammatory responses resulting in damaging fish’s body organs. This bacteria damages the liver and kidneys most, which makes the fish dropsy.

Which types of fish can get TB?

The bacteria usually infect weakly, stressed, or old fish with a compromised immune system but may affect the entire population. The most vulnerable and susceptible groups of fish are:

 Labyrinth fish

  • Betta fish
  • Gouramis


  • Giant danio
  • Guppies
  • Golden carp
  • Goldfish
  • Pike-perch
  • White cloud mountain minnow


  • Sword-tails


  • Black widows
  • Neon tetra



  • Fire-mouth cichlid
  • Ramirez’ dwarf cichlid
  • Egyptian mouth-brooder
  • Angelfish


  • European catfish

How do you treat TB in fish?

Fish tuberculosis is not easy to treat and takes a long period; it requires supportive care. You can not eliminate the bacteria out of the body, and the fish continues to live with the infection.

Quarantine the infected fish

The most effective way is to depopulate the tank to avoid cross-contamination in-case other animals are free from infection. Quarantine your infected fish for treatment with antibiotics, and it is better to keep it in a hospital tank.

Clean and sanitize the whole system

Clean the system with bleach to disinfect it and remove organic materials and bio-films. Only bleach is not enough as the bacteria is resistant to many disinfectants, so use Lysol. Discard the substrate and plants and sterilize all the equipment and decorations.


Although the TB bacteria are resistant to many drugs and medications, three antibiotics are best for TB. Isoniazid, kanamycin, and neomycin antibiotics help treat diseases and reduce symptoms. 

Sometimes sulfamethazine or trimethoprim combination is also helpful in treating TB. However, survival expectations are below fifty percent and can take a long time to cure completely. You should know methods to treat a sick fish in an aquarium.

Fish bath

Along with the medications, when you give a fish bath, it can be a hope of success. A Usena fish bath with methylene blue for 30 minutes is helpful too, but do not use any other antibiotic in the fish-bath with Usena.

Boost the immune system

Add vitamin C in the water to help improve the immune system of fish. You can also use a water conditioner containing vitamin C in it. 

Raise the water temperature to 70-80 degrees Fahrenheit.

Use UV light or sterilizer in the water to reduce bacteria count, and it also helps reduce the burden from the immune system.

Increase the production and growth of beneficial bacteria by adding a lot of biological filtration to the tank. 

How to prevent TB in fish?

Proper cleaning and sanitation

Proper cleaning and sanitation help prevent the development and spread of disease. Remove all the wastes, residues, worms, debris, and contamination from the tank at least every weak otherwise your fish can have a bent body.

Throw all the broken branches or deteriorated plants out of the tank and remove algae and bio-films. Change tank water frequently and wipe all the surfaces and corners properly. Clean the substrate, rocks, all equipment, and decorations and sterilize or sanitize them well. You can use a gravel cleaner in the aquarium.

Provide a balanced diet

The diet or feed you are providing fish should be healthy and nutritious. Put extra attention and dedication into choosing the right animal feed. Feed them to live frozen food instead of fresh live food. Monitor the animal’s health and provide them food that is free from contamination and bacteria.

Water conditions

Maintain the water temperature, oxygen level, and pH of the water to ensure fish health. Also, avoid crowding in the tank because overcrowding is one of the risk factors for the disease. You should also stop brown algae from growing in the aquarium.

It is better to use UV sterilizer regularly to kill bacteria in the water, otherwise, it can also cause Popeye disease in fish.

Fish TB is contagious to humans

This bacteria can also affect humans when transmitting from fish to humans. Some people can get this bacteria while swimming in the ocean, but this is rare. Mostly, when the aquarium owner clean or put the bare hand in the aquarium’s water without knowing the presence of bacteria, it catches TB. 

Also, while handling certain fish having pointy fins, such as catfish, one can get punctures on the hand, and the bacteria can enter inside the body. The bacteria enter through broken skin or open wounds on the hands.

The bacteria does not severely affect healthy individuals but causes damage to weak and immune-compromised persons. Hence, it is preferable to wear aquarium gloves before maintaining the tank and curing an infected animal.