Common Fish Diseases In Fish Farming

Fish diseases
Fish diseases

In Fish farming, now and then, harmful micro-organisms cause fish diseases that affect the health and growth of fish. 

These diseases are generally called fish diseases. Micro-organisms that cause fish diseases include:

  1. Bacteria
  2. Fungi
  3. Virus
  4. Protozoa
  5. Nematode, etc.

Harmful microorganisms pose a serious threat to the aquatic ecosystem and aquaculture industry. The ability to identify fish diseases caused by harmful micro-organisms and the ability to control fish diseases is very important to the success of a fish farming business.

Fish diseases
Diseased fish

In this article, we will teach you how to identify fish diseases, the causative agent, and the treatment. Fish diseases left untreated in an aquarium can wipe out an entire investment.

Some of these diseases caused by harmful micro-organisms are easy to discover and treat. While others are difficult to identify and hence need a more careful examination before they can be discovered.

Major symptoms to look out for in bacterial diseases are swollen abdomen and eyes, red spots. While for Fungal infections, there is a visible sight of the parasite growth.

Below is a list of fish diseases, causes, symptoms, and treatment.

Hemorrhagic Septicemia

Causative agent: Bacteria.

Hemorrhagic Septicemia is most times introduced to a fish population by an already infected fish that is brought into the pond.

Symptoms: Bruised-like red coloured eyes, gills, and skin. Bulging eyes, distended abdomen, and open sores.

Treatment: There is no particular known treatment yet. But the use of broad-spectrum antibiotics like Chloramphenicol and tetracycline has proved to be helpful in controlling this particular fish disease and reducing in fish mortality rate.


Causative agent: Bacteria.

Dropsy (also called water sickness), is a bacterial infection that affects the kidney of fish, which results in fluid retention. Poor water quality and harmful micro-organisms in the water are other causes of Dropsy (water sickness).

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

Treatment: The treatment of this fish disease is usually by the application of parasite treatment to the fish pond for at least two days, Examination and improvement of the water quality, regulation of temperature and ammonia level, and the administering of antibiotics like Chloramphenicol and tetracycline to flake food in the proportion of 250mg of antibiotic to 25g of food.


Causative agent: Fungi

This is majorly caused by poor water quality and the decomposition of food materials in the fish pond as a result of overfeeding.

When too much feed is given to the fishes, after eating to their satisfaction the remnants settle at the bottom of the pond, decompose and cause saprognia.

Symptoms: Whitish or greyish growth like cotton wool appears on the skin, mouth, or fins of fishes. This leads to increased mortality and slow growth if left untreated.

Treatment: Usage of fungal treatment for a minimum of four days.

Fish diseases

Fin and Tail Rot

Causative agent: Bacteria.

Fin Rot is usually a symptom of other diseases, but on rare occasions, it can also occur on its own. It is an indication of bacterial infection, which deteriorates fish immunity and results in the fraying of fins and tails.

Symptoms: Tails and fins begin to lose colour, deterioration in the physical appearance of fins and tails, reddened fins, and skin ulcers.

Treatment: Usage of good antibiotics to treat the water and infected fishes. You can use Chloromycetin.

Ich (Ichthyphthirious)

Causative agent: Fungi

Ich occurs as a result of a rapid increase in temperature and pH of water.

Symptoms: Gasping and heavy breathing at the water surface of the pond, White salt-like spots on the skin, fins, and tail of fishes.

Treatment: Treatment can be done with quinine hydrochloride or quinine sulphate at 30mg per litre of water.

Mouth Fungus

Causative agent: Fungi

Mouth fungus becomes fatal due to the production of toxins and loss of appetite.

Symptoms: White cotton-like patches around the mouth/lips of fishes.

Treatment: Use antifungal and antibacterial drugs like Chloramphenicol at 10 to 20mg per litre of water. Repeat after two days.


Causative agent: Virus

Lymphocytis is caused by a virus that attacks the fish cells. It is highly infectious.

Symptoms: Large white lump (cauliflower) growth on the fin, tail, or other parts of the fish body.

Treatment: It is a very infectious viral disease and has no known treatment. But to control the viral infection, remove and terminate infected fishes or isolate for months to see if there will be recovery, which is also a possibility.

Flukes (Gyrodactylus)

Causative agent: Fluke worm
It is caused by microscopic worms or worm-like parasites introduced to the fish population by plants around the pond position.

Symptoms: Skin irritation causing fishes to scratch themselves against pond walls or any object in the pond. Rapid opening and closing of gills. Gasping at the pond surface.

Treatment: Bath the infected fish in 10mg of potassium permanganate in one litre of water. Table salt can be used in place of potassium permanganate to bathe the fish for two or three days.

You can also use Sterazin for 10 days to destroy the parasites in the entire pond

Lernaea/ Anchor Worm

Causative agent: Parasitic worm

Parasitic worms burrow into the skin of fish and lay eggs in their muscles. It usually enters the fish tank through the introduction of already infected fish to the fish population.

Symptoms: Body inflammation, tiny red worms, and white-green worms in wounds, difficulty in breathing, general lethargy.

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

Food Deficiency

Fish diseases
Fish feed

Another common poor health condition in fish is food deficiency. Insufficient and inadequate food nutrient is a disease of its own as it causes a breakdown of the body.

Symptoms: Weakness and slow growth.

Treatment: Proper feeding and supply of nutritious feed to the fishes.

Fish Diseases Precautionary Measures

There are some precautionary measures you can employ to minimize the occurrence of fish diseases.

• Set up an isolation tank to transfer sick fish. Treatment of fishes is more efficient in isolation than treating a whole population especially in a large fish pond that is stocked to capacity.

• Include water management and treatment in your routine general fish health management practice. Poor water quality plays a large role in fish diseases introduction to the fish population.

• Addition of multivitamins to the fish treatment can help build up their immune system.


The practice of good fish health management will go a long way to reduce the occurrence of fish diseases in a fish population. It is usually cheaper to practice good fish health management than to treat fish disease.

Fish diseases
Fish diseases

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