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Fish Diseases, Symptoms and Control Methods

Fish Diseases, Symptoms and Control Methods

Fish Diseases:

The following information is about Fish Diseases and Prevention Measure in Fish Farming:

The following are some major diseases of fishes. The diseases are;

  • Bacterial Diseases.
  • Fungal Diseases.
  • Parasitic Diseases.
  • Protozoan Diseases.
  • Non-Infectious Maladies.
  • Miscellaneous Diseases.
  • Viral Diseases.

Bacterial Fish Diseases:

Bacterial diseases generally categorized by red streaks or spots or swelling of the abdomen or eye.

Read: Fish Farming FAQs.

Red Pest:

  • Symptoms: The main symptoms of this disease are bloody streaks on body, fins and tail. If the infection is severe, this disease leads to ulcers followed by fin and tail rot and falling off. This is internal diseases and an external treatment doesn’t work. There are no external treatments for this disease.
  • Prevention: Once you observe the disease symptoms, treat the tank with a disinfectant and clean the tank properly. To clean tank use acriflavine or monacrin. Supply limited feed white treating them with disinfectant. If the disease is not controlled with disinfectant, add some antibiotics. The best antibiotic to treat red pest disease is Chloromycetin and tetracycline.

Mouth Fungus:

  • Symptoms: you can observe white cottony patches around the mouth. These spots look like a fungus attack of the mouth. The Chondrococcuscolumnaris is a bacterium which is the root cause of this disease. At the early stages, the infection appears like a grey or white line appear around the lips and later turns to fungus. Production of toxins and the inability to eat is the root cause of the disease.
  • Prevention: Penicillin is effective treatment for this disease.


  • Symptoms: the symptoms this disease can be emaciation, hollow belly, possibly sores. Mycobacterium piscium is a bacterium which is the root cause of Tuberculosis. The infected fish will become hollow bellied, pale, show skin ulcers and frayed fins, and loss of appetite. Overcrowding and poor sanitation are the root cause of this disease.
  • Prevention: there is no particular treatment for this disease. The best prevention measure is to destroy the infected fish. Don’t overcrowd the tank and maintain proper sanitation.


  • Symptoms: The main symptoms are bloating of the body, protruding scales. Dropsy is a bacterial infection of the kidneys, which leads to fluid accumulation or renal failure. When the infection is severe, the fluids in the body build up and cause the fish to bloat up.
  • Prevention: Adding an antibiotic to the food can be the best treatment for this disease. Chloromycetin (chloramphenicol), or tetracycline are best antibiotics to treat this disease.

Scale Protrusion:

  • Symptoms: the main symptoms of this disease are protruding scales.
  • Prevention: Adding antibiotic to the food is the best method to treat this disease. Chloromycetin or tetracycline is the best antibiotics to treat this disease.

Tail Rot & Fin Rot:

  • Symptoms: the major symptoms are disintegrating fins, exposed fin rays, blood on the edges of the fins, reddened marks under the fins, skin ulcers, cloudy eyes. This is mainly caused due to Aeromonas. The improper tank environment is the root cause of this disease which can be caused from a simple injury to the fins. Severe infection can lead discoloring of the tail.
  • Treatment: You should treat the water or fish with antibiotics. Chloromycetin or tetracycline is the best antibiotics to treat this disease. Treatment the tanks with CuSO4 can give effective results.


  • Symptoms: the major symptoms of this bacterial disease are loss of appetite and slow body movements. Haemophilus is the bacteria which causes ulcers.
  • Treatment: Treatment the fish tanks with 1% CUSO4. Antibiotics like Oxytetracycline and chloramphenicol are best to treat this disease.

Treating Bacterial Diseases:

  • Penicillin, amoxicillin, or erythromycin is the best antibiotics to treat bacterial diseases. Antibiotic usage can disturb the biological environment in the tank, during treatment monitor the ammonia and nitrate levels in the water.

Read: RAS Fish Farming.

Fungal Fish Diseases:


  • Symptoms: the main symptoms of this fungal infection are fish starts to scrape itself against objects, clamped fins, and parasites are visible on the body of the fish. The fish louse gets flattened. The infected fish will irritate the host fish which may have clamped fins, become restless.
  • Prevention: Light infestations, can be controlled by picking of the lace. And treat water with potassium permanganate in case severe infection.


  • Symptoms: the major symptoms are sluggishness, loss of balance, hollow belly, external cysts and sores. This infection mainly attacks the liver and kidneys. The infected fish will become sluggish, loosely balanced with show hollow bellies.
  • Prevention: AddingPhenoxetholor Chloro­mycetin to feed can be an effective solution. At early stages, it is recommended to destroy the affected fish.

Fungus (Saprolegnia):

  • Symptoms: you can observe tufts of dirty, cotton-like growth on the skin, and the fish eggs turn white. This fungal infection can lead to parasitic attack, injury, or bacterial infection.
  • Treatment: Treat the tank water with phenoxethol and the chemical application should be limited. In case of severe infections, remove the infected fish and treat it with iodine or mercurochrome.

Parasitic Fish Diseases:

Velvet or Rust:

  • Symptoms: you can observe yellow to light brown “dust” on the body, clamped fins, and respiratory distress. The infected fish will get irritation, low appetite and breath problems.
  • Prevention: Treat the water with copper once in a week. And water should be changed after treatment.

Anchor Worm:

  • Symptoms: The fish infected with this disease will scrape itself against objects, and you can observe whitish-green threads hang out of the fish’s skin.
  • Prevention: give a complete bath for 15 to 30 minutes for infected fish in potassium permanganate. Treat the whole tank with potassium permanganate, which not much recommended.


  • Symptoms: the infected fish will scrape it against the objects, you can observe green thread hanging from fish gills.
  • Prevention: treat the infected fish with potassium permanganate for 10 to 30 minutes.


  • Symptoms: The infected fish will scrape itself against objects and you can mucus covering the gills or body, the gills or fins may be eaten away, the skin turns reddened. In case of severe infestation fish turn pale with drooping fins, rapid respiration with hollow bellies.
  • Prevention: the infected fish should be given 10 to 30-minute bath in potassium permanganate.


  • Symptoms: the symptom is worms hanging from the anus. A heavy infestation can cause hollow bellies.
  • Prevention: Soak the fish feed in para-chloro-meta-xylenol and give the fish a bath or treat the tank. Or feed the special food with thiabendazole which cures nematodes effectively.


  • Symptoms: You can observe leeches on the fish’s skin. These are heart shaped worms they suck and borrow the surface of the fish which causes death of the fish.
  • Prevention: Give fish a 10 to 30 min bath in salt solution. Another treatment is to treat them with Trichlorofon which is more effective in case severe infections.

Protozoan Diseases:


  • Symptoms: The skin turns milky.
  • Treatment: This is a rare disease that causes a cloudiness of the skin. Treating infected fish or tank water with copper can give effective results. Acriflavine can be a best medicine, which sterilizes the fish and water.


  • Symptoms: This disease mainly caused due intestinal flagellated protozoa which infect the lower intestine. It is digestive tract disease and caused loss of appetite.
  • Treatment: Metronidazole can be a best medicine to treat this disease. The medicine can be added to food and water. Water treatment should be every week.

Neon Tetra Disease:

  • Symptoms: white patches deep in the fish flesh are the main symptom of this disease. It causes muscle degeneration, which leads abnormal swimming.
  • Prevention: there is no exact cure for this disease. Just destroy the infected fish and clean the tank and fill with fresh water.

Glugea and Henneguya:

  • Symptoms: The infected generated white swellings on the fins and the body. This disease is very rare.
  • Prevention: this sporozoans form large cysts in the fish’s body and release spores. The best and effective method is to destroy the infected fish before the infection spreads.

Hole in the Head

  • Symptoms: the main symptoms are small holes on the head of fish, if the infection is severe fish show markings along the lateral line of the fish. Fish stops eating. Poor water quality and lack nutrition are the main reasons for this disease.
  • Prevention: Vitamin enriched foods. Supply food made of NLS Hex Shield Fish Food.

Viral Fish Disease


  • Symptoms: the major symptom is nodular white swellings on fins or body. This virus affects the cells of the fish. It is a rare disease in fish farming.
  • Prevention: the best method control this disease is to remove and destroy the infected fish. Or separate the infected fish and treat it with antibiotics till it gets normal.

Miscellaneous Fish Diseases:

Some miscellaneous diseases in fish are eye diseases, swim bladder diseases which are rare and caused due to lack of nutrition’s in food.

Most of the fish diseases are caused due to stress in fish being due to transport, improper acclimation and water quality issues. Good sanitation and proper oxygen levels keep fish healthy.

Read: Tuna Fish Farming.

Last Updated: October 27, 2018
Author: Jagdish

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