20 Major Fish Diseases: Causes, Symptoms, Preventions and Treatments

Alt: = "photo of fish infected with fungus"
Fungus Infected Fish

Published: 03 December 2021
Updated: 15 November 2023


There are many pests and diseases that affect the health and growth of fish. These pests and diseases can be: 

  • bacterial, 
  • parasitic, 
  • fungal,
  • Viral,
  • protozoan,
  • abiotic infections,
  • noninfectious maladies, etc

Pests and diseases pose a serious threat to the aquatic ecosystem and aquaculture industries. Being able to identity fish pests and fish diseases, and control them is very important to the success of fish farming business. As a fish farmer, it is important for you to have the knowledge to identify these diseases, causes, symptoms and appropriate treatments. Disease in aquarium can wipe out an entire investment.

This article tries to outline the common fish diseases, their symptoms, causes and treatment.

Major symptoms to look out for bacterial diseases are swollen abdomen and eyes, red spots. Major symptoms for Fungal diseases is the visible sight of the parasites. 

Read also: How to Run Catfish Business Profitably in Nigeria

Fish Disease

1. Hemorrhagic Septicemia

Disease Type: Bacterial disease

Causes: Hemorrhagic Septicemia is introduced to a fish population by already infected in coming fish.

Symptoms: Bruised-like red hue to eyes, skin and gills. Bulging eyes, open sores, distended abdomen. Bleeding of the internal organs and skin.

Treatment: There is no known treatment yet. But you can use multipurpose antibiotics like Chloramphenicol, or tetracycline to control the disease and reduce mortality.

2. Dropsy 

Disease Type: Bacterial disease

Causes: It is a bacterial infection that affects the kidneys  of fish, which causes fluid retention. Poor water quality and microorganisms in the water are other causes of Dropsy.

Symptoms: Weakness, loss of appetite, swollen abdomen and scales.

Treatment: Apply parasite treatment to the fish pond for 2 days. Examine and improve the water quality, temperature, ammonia levels which are the underlying causes of stress to fish. Add antibiotics like Chloramphenicol or tetracycline to flake food in proportion of 250mg to 25g respectively.

3. Fin and Tail Rot 

Disease Type: Bacterial disease

Causes: Fin Rot is usually symptoms of other diseases, but it can also occur on its own. It is a sign of bacterial infection, which breaks down fish immunity and results to fraying of fins and tails.

Symptoms: fray or colour loss of the tails and fins, deterioration of fins and tails, blood around the edges of fins, reddened fins, skin ulcers.

Treatment: Use good antibiotics to treat the water or infected fish or both. You can you Chloromycetin (Chloramphenicol) or tetracycline.

4. Scale Protrusion 

Disease Type: Bacterial disease

Causes: It is caused by the bacteria that infects scales or body.

Symptoms: Protruding of the scale and sometimes the body too.

Treatment: Add antibiotics to the food. Add about 1% of Chloramphenicol, or tetracycline, or any other antibiotics.

5. Ulcer 

Disease: Bacterial disease

Causes: Fish ulcer is caused by bacteria, and haemophilus.

Symptoms: Slow movement of the abdomen, loss of appetite.

Treatment: Give dip treatment in 1% CUSO4 for 1 minute for 3 – 4 days. In the case of severe infection, use oxytetracycline  or Chloramphenicol.

6. Red Pest 

Disease: Bacterial disease

Causes: It is a bacterial caused disease that caused streaks on fish body, fins and tails.

Symptoms: Streaks or spots on the body, fins and trails which appear red.

Treatment: Use of acriflavine (trypaflavine), myxazin or monacrin (monoamio-acridine) to disinfect and clean the fish tank. The solution should be of 1ml per litre of water. Note: the disinfectant changes the colour of the water for a while and turns normal as disinfectant dissipates.

7. Tuberculosis 

Disease Type: Bacterial disease

Causes: Bacterium Mycobacteria Piscium, and overcrowding of fish in an unclean environment

Symptoms: Hollow belly, skin sores, loss of appetite, and fish emaciates.

Treatment: Disinfect the tank, reduce the number of fish in the tank as overcrowding is usually the main cause of the disease.

8. Mouth Fungus 

Disease Type: Bacterial disease

Causes: Bacterium Chondroccus columnaris. It is usually fatal due to toxins production and loss of appetite.

Symptoms: As the name suggests, white cotton-like patches around the mouth, lips.

Treatment: Use antibiotics like: (a) Chloramphenicol at 10-20mg per litre of water. Repeat after 2 days. Or (b) Penicillin at 10000 per litre of water. Repeat in 2 days time.

9. Saprognia/ Fungus 

Disease Type: Fungal disease

Causes: It is commonly caused by poor water quality and decomposing materials in the aquaculture. In rare cases fungus can develop as a result of another infection in a fish.

Symptoms: White or grey growth that looks like cotton wool on the skin, mouth or fins. Leads to mortality, if left untreated.

Treatment: Use any fungal treatment for four days.

10. Ich (Ichthyphthirious)

Disease Type: Fungal disease

Causes: Rapid water temperature increases and pH variations

Symptoms: Rapid breathing or gasping at the water surface. Itching itself at the tank body or any other object in the pond due to irrigated skin. White salt like spots on the skin, fins, tail. Clamped fins.

Treatment: Treat with quinine hydrochloride or quinine sulphate at 30mg per litre of water.

Alt: = "photo showing fish with white spots on its skin, fins, tail a sign Ich disease"

11. Lymphocytis 

Disease Type: Viral disease

Causes: It is caused by virus that attacks the fish cells. It is very infectious

Symptoms: Abnormal large white lump (cauliflower) growth on the fin or other parts of the fish body.

Treatment: It is a very infectious virus and has no known treatment. But to control the viral infection, remove and destroy infected fish or isolate for months to see if it can recover, which is possible.

12. Flukes (Gyrodactylus)

Disease Type: Parasitic disease

Causes: It is causes by microscopic worm-like parasites introduced to the fish population through already infected incoming fish or by plants around the tank position.

Symptoms: Irritation of the skin causing fish to itch itself against tank wall or any objects in the tank. Visible mucus on the gills. Rapid opening and closing of gills. Gasping at the surface of the water. May lead to loss of gills and mortality in severe case.

Treatment: Bath the infected fish in 10mg of potassium permanganate per litre of water. You can use salt in place of potassium permanganate to bath the fish for two to three days. You can also use Sterazin for 10 day to destroy the parasites in the entire tank.

13. Lernaea/ Anchor Worm 

Disease Type: Parasitic disease

Causes: Parasites that burrow into the skin of fish and lay eggs in their muscles. It usually enter the fish tank through the introduction of already infected fish 

Treatment: Disinfect the water with a single dose of water treatment like Aquarium Rescue Parasites Control or Potassium Permanganate.

14. Bio-disease

Disease Type: Protozoan disease

Causes: It is caused by protozoa,  Myxobolus pfcifferi.

Symptoms: Large boils of different sizes appear on the body.

Treatment: Birth the infected fish in 3% common salt solution or 1% formalin solution for 10 minutes.

15. Leeches 

Disease Type: Parasitic disease

16. Nematodes 

Disease Type: Parasitic disease

17. Tumour 

Disease Type: Noninfectious Maladies

18. Congenital Abnormalities

Disease Type: Noninfectious maladies

19. Physical Injuries

Disease Type: Noninfectious maladies

20. Vervet/ Rust

Disease Type: Parasitic disease

Alt: = "photo showing fish tail infected with vervest/rust"

Other Common Health  Conditions in Fish

1. Temperature Stress

Symptoms: lethargy, mortality of cold intolerant (hypothermia) or hot intolerant (hyperthermia) fish, mold disease (hypothermia), dyspnea (hyperthermia).

Treatments: Insulate the tank, ads a water heater, house the system in a greenhouse in cold seasons (hypothermia). Shade the tank wall, ventilate at night, set up a cooling system (hyperthermia)

2. Ammonia Poisoning

Disease Type: Gas bubble disease 

Causes: rapid increase of temperature or rapid decrease of water pressure that reduces the gas solubility, use of groundwater, excess water oxygenation.

Symptoms: fish floating to surface, popped eyes due to gas emboli, presence of emboli in blood and any organs, including eyes, skin and gills.

Treatments: reduce the gas in excess, avoid stress to fish during recovery.

3. Food Deficiency

Causes: Lack of proper and adequate food nutrient is a disease of it own as it breaks down body defense. Constipation (Indigestion)

Symptoms: poor growth, depression, mortality, abnormality in the skeleton, ocular lesion, anaemia, blindness and excessive fat accumulation.

Treatment: Follow the fish requirements, vary the diet, provide specific pellet feed for fish, provide vitamins and minerals, balance protein : fat ratio and decrease fat (fat accumulation).

4. Eye Problems

5. Sim-Bladder Disease

6. Head & Lateral line Disease

7. Constipation (Indigestion)

Fish Diseases Treatment Precautions

Set up a hospital or isolation tank. It is more effective to treat infected fish in isolation than in a whole population especially if the fish pond is large and stocked to capacity.

Remove any activated carbon for the period of treatment.

Include water treatment in your routine fish health management practice. Poor water quality plays large rule in fish diseases introduction through stress.

Addition of multivitamin treatment can help build up the immune system of the fish.

Related article: Solutions to Fish Farming Problems in Nigeria

Ikechukwu Evegbu

Ikechukwu Evegbu is a graduate of Statistics with over 10 years experience as Data Analyst. Worked with Nigeria's Federal Ministry of Agriculture and Rural Development. A prolific business development content writer. He's the Editor, Business Compiler

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