Fish Farming: Treatment and control of common fish diseases


Fish farming is a profitable business and easy on pocket, but sometimes diseases go unnoticed and hence the whole purpose is toppled. Diseases pose a major threat to aquaculture. A loss to the tune of 10-15% of production cost may be incurred due to disease problems. Hence, it is essential to take care of ponds and hatcheries to prevent the disease spread.

Mortality in fish often is noticed due to poor management of ponds and hatcheries. The pond environment, particularly the water quality in ponds and hatcheries play crucial role in causing mortality and triggering infection.

Health care management in Fish farming
Health care management in Fish farming

Water Quality parameters:

Hence, to prevent any disease or mortality problems, the following water quality parameters should be maintained in the mentioned range :

  1. pH : 7.5 to 8.5,
  2. Dissolved oxygen: > 5.0 ppm
  3. Temperature: 25-30 °C
  4. Total alkalinity: 75-175 ppm
  5. Total hardness: 75-150 ppm

Ponds need to be limed and fertilized at regular intervals to maintain optimum water quality and load of fish food organisms. The common management problems that lead to mass or large scale mortality in farms and their preventive measures are given hereunder. Further, the fish farmers are advised to contact fish health experts once any disease signs are noticed in a pond or mortality recorded, if any, to prevent further spread of infection to nearby ponds.

A health management program and a disease emergency plan are essential documents on farms. As many farmers have recognized, the frequency and severity of disease outbreaks in ponds seem to depend on a number of factors, not all of them were well understood. The first point to appreciate is that not all diseases are infectious. For example, some are caused by toxins, others by nutritional imbalances. The following section focuses on infectious diseases because their causes are usually complex and control and prevention can be more challenging. Infectious disease outbreaks in ponds depend on particular interactions between the host, the pathogen and the pond environment.

The major disease problems that occur in aquaculture ponds are parasitic, fungal, and bacterial in origin. Important disease problems that generally encounters are argulosis, LIRNEasia, protozoan diseases caused by Trichodina, Costia, Ichthyobodo, Myxosporidean diseases, gill flukes such as Dactylogyrus, and Gyrodactylus; fungal diseases such as saprolegeniasis, branchiomycosis, Epizootic Ulcerative Syndrome; bacterial diseases such as aeromoniasis (fin and tail rot)/red disease, edwardsiellosis and Columnaris. Besides these, algal bloom is a major problem that depletes the dissolved oxygen in the ponds.

Important indicators of disease or infection in a fish pond

The following common symptoms are mostly seen in diseased fish due to different disease:

=> Loss of appetite

=> Poor growth of fish

=> Air gulping and surfacing

=> Flashing movement of fish and rubbing against hard objects

=> Floating on the water surface with different abnormal postures

=> Fin and tail rots

=> Slow movement of fish in a pond

=> Haemorrhages on body and/or gills

Principles of fish health management

The principles of fish health management incorporates
i. Minimizing stress in cultivated fishes
ii. Confinement of disease outbreak to affected ponds
iii. Minimizing losses from disease outbreak.

This could be achieved through prophylaxis and positive treatment to the outbreak of epidermics. Because of the aquatic ambiance, it is not easy to get aware of the activities of fish. It is difficult to conduct a correct diagnosis and timely treatment. This necessitates prevention of fish diseases which is more important than control of fish diseases. This signifies the importance of the statement “Prevention is better than cure”.

General preventive measures

Internal resistance: Increasing the internal resistance of fish is important in the prevention of diseases. Therefore, some additional points in fish culture are advisable.

  1. Selection of healthy fish seeds.
  2. Proper density and rational culture.
  3. Proper pond management
  4. Qualitatively uniform ratio and quality food
  5. Good water quality
  6. Prevention of fish body from injury
Medium for fish diseases
Water seems to be mainly responsible for various diseases since the vital functions of fish viz. movement, feeding, digestion, assimilation, growth, responses to stimuli and reproduction are dependent on water

Common symptoms of diseases are:
  1. Unusual movements
  2. Abnormal and unhealthy look
  3. Discoloration
  4. Film like covering on the skin
  5. Swelling or spots on the skin
  6. Pale gills, white and red spot on gills
  7. Excess slime secretion
  8. Sources of infectious diseases
  9. Primary source: Sick fish serves as a primary infectious source and are the carriers of pathogens. The pathogen infects through direct contact or by discharge of disease causing agents into the water.
  10. Secondary source: Water coming from diseased ponds, contaminated silt, feeds and gears.
  11. Natural resistance of fish to infectious diseases
  12. Surface texture of skin and mucous membrane of fish functions as a screen to keep the infectious micro-organisms out of it.
  13. Lysozyme secreted from the cell can kill bacteria.
  14. The pathogenic microbes entering into digestive tract will be under the influence of digestive enzymes which can kill pathogens
  15. The phagocytotic function of white blood cells. Lymphoid cells, reticuto-endothelial cells of spleen, liver and blood vessel can eliminate foreign body as well as pathogenic micro-organisms.
  16. Blood of fish contains bactericidin which can eradicate all kinds of pathogenic bacteria.

Types of diseases

Diseases which affect fish are parasitic and non-parasitic. The former includes those caused by bacteria, fungi, protozoans, worms, leeches and copepods and the latter comprise disorders associated with nutritional deficiency and sudden changes in abiotic and biotic factors. The common symptoms by which the affected fish are recognized are (a) changes from normal behavior, (b) signs of reduced vitality, (c) lack of appetite and failure to feed, and (d) presence of lesions or sores

Bacterial Diseases

Disease: fin and tail rot
Causative organisms: Aeromonas, Pseudomonas and Vibrio
Symptoms: White line on the margin of the fin; fin rays become brittle and start breaking.
Treatments: 1 minute dip treatment in 500ppm copper sulphate solution.

Disease: Ulcer disease
Causative organisms: Aeromonas hydrophilla and Pseudomonas
Symptoms: Open sores or ulcers on the body.
Treatments: Dip treatment for 1 minute in 1:2000 copper sulphate solution for 3-4 days.

Disease: Dropsy
Causative organisms: Pseudomonas punctata
Symptoms: Accumulation of fluid inside the body cavity; scale protrusion; exophathalmic condition.
Treatments: Dip treatment in 5ppm potassium permanganate solution for 2 minutes.

Disease: Eye disease
Causative organisms: Aeromonas liquifaciens
Symptoms: Cornea of eye becomes vascularised and later becomes opaque eye ball gets decayed.
Treatments: Chloromycetin (8-10 mg/liter) bath for 1 hour for 2-3 day.


Disease: Water – mold disease (Saprolegniasis)
Causative organisms: Saprolegnia parasitica
Symptoms: Dies after ulceration or exfoliation of skin followed by haemorrhage blindness, tufts of white hair like out-growth in the affected region.
Treatments: Dip treatment for 3seconds in 1:10,000 solution of malachite green or for 5-10 minutes in 3% common salt solution or potassium permanganate


Disease: Ichthyophthiriasis (White-spot disease)
Causative organisms : Ichthyophthirius multifilis
Symptoms: Small whitish-cysts of about 1mm diameter on the skin, gills and fins.
Treatments: 5 days bathing in 2ppm methylene blue, hourly dip treatment in 1:5,000 formalin solution for 7-10 days.

Disease: Boil disease

Causative organisms: Myxobolus pfeifferi
Symptoms: Large boils varying from the size of a nut to that of a hen’s egg on several parts of body.
Treatments: Bath in 3% common salt solution or in 1:2,500 formalin solution for 10 minutes.

Disease: Whirling disease
Causative organisms: Myxobolus cerebrails
Symptoms: Caudal bend, deformity of the oral region and blackening of tail region.
Treatments: Destroy all infected fish by applying quicklime (pond disinfectant) at the rate of 2t/ha.

Disease: Costiasis
Causative organisms: Costia necatrix
Symptoms: Bluish-coating on the skin, lesions as irregular patches.
Treatments: Bath in 3% common salt solution or in 1:2,500 formalin solution for 10 minutes.


Disease: Gyrodactylosis
Causative organisms: Gyrodactylus sp.
Symptoms: Fading of colours, drooping of scales, peeling of skin.
Treatments: Dip treatment in 5% common salt solution or in 1:5,000 formalin solution for 5 minutes.

Disease: Dactylogyrosis
Causative organisms: Dactylogyrus sp.
Symptoms: Fading of colours, drooping of scales, peeling of skin.
Treatments: Dip treatment in 5% common salt solution or in 1:5,000 formalin solution for 5 minutes.

Disease: Diplostomiasis (Blacki-spot disease)
Causative organisms: Diplostomulum sp.
Symptoms: Small black nodules of about 1-5mm diameter in the affected region.
Treatments: Dip treatment in 3:1,00,000 picric acid for 1 hour, Di-n-butyl tin oxide at the rate of 250mg/kg fish.


Disease: Ligulosis
Causative organisms: Ligula sp.
Symptoms: Dull, sickly and with parts of alimentary canal swollen or completerly choked by cestoded cysts or worms.
Treatments: Dip treatment in 3:1,00,000 picric acid for 1 hour, Di-n-butyl tin oxide at the rate of 250mg/kg fish.


Causative organisms: Philometra sp., Camallanus sp.
Symptoms: Dull, sickly and with parts of alimentary canal swollen or completerly choked by round worms.
Treatments: Dip treatment in 3:1,00,000 picric acid for 1 hour, Di-n-butyl tin oxide at the rate of 250mg/kg fish.

Causative organisms: Acanthogyrus sp.
Symptoms: Yellowish white fibro epithelioma on lip, skin and fin.
Treatments: Quick lime.

Causative organisms: Hemiclepsis sp.
Symptoms: Abnormal movements of the fish due to irritation as the parasites feed on the blood of host.
Treatments: Dip treatment in 1:1,00,000 solution of glacial acetic acid.

Causative organisms: Argulus sp., Ergasilus sp., Lernea sp., Caligus sp., Pseudocycnus sp., Clavellisa sp.
Symptoms: Loss of scales and presence of red spots, damage of gills.
Treatments: Half an hour treatment in 500ppm formalin solution, mechanical removal by forceps followed by a bath in weak potassium permanganate solution for 2-3 minutes, bath in 1:1,000 glacial acetic acid solution for 5 minutes and subsequent bath in 1% common salt solution for 1 hour, pond may be disinfected by applying lindane at the rate of 8ml/1,000 litre.


Disease: Lymphocystis
Causative organisms: Lymphocystis spp. (A DNA Iridovirus)
Symptoms: Lethargy, may affect balance and swimming control if along the lateral line.
Treatments: Frequent water changes and reduction of ammonia and nitrites in water may reduce stress to help the fish battle the infection and shrink tumors on its own.

Disease: Infectious Pancreatic Necrosis- (IPN)
Causative organisms: IPN virus
Symptoms: Darker in color, tail chasing, spiral swimming behavior. Treatments: uncontaminated water supply, providing optimum feed.

Miscellaneous Diseases

Gas bubble disease

When nitrogen of the water is in saturation, due to rapid temperature changes, gas bubble disease may result and fish fry particularly, die in large numbers. Fish affected by this disease often swim at an angle of 450 with head pointing down. Other symptoms are the presence of bubbles beneath the skin, on fins, around eyes in stomach and intestine or in blood capillaries. In such conditions, water should be well agitated to bring down the nitrogen saturation or affected fish should be transferred to other ponds. Besides, nitrogen, supersaturated levels of oxygen have also been reported to cause gas bubble disease in fishes.

Vitamin Deficiencies

• Scoliosis (Curved Spine)
• Reduced Growth
Anorexia (Lack or Loss or Appetite)
• Low fish weight
• Lethargy

Types  of  Treatment

Dip- In the dip treatment, fish are kept in a relatively strong solution of the chemical for a very short time, usually less than one minute. Proceed as follows:

I. Prepare the chemical solution in a bucket, half-drum or trough;
II. Place the fish or a batch of fish in a dip net;
III. Dip the fish for the prescribed duration into the solution;
IV. Immediately after the treatment, replace the fish in well-aerated water.

Bath treatment:

In the bath treatment, fish are kept in a weaker standing solution of the chemical for a longer period of time, which may last from a few minutes to one hour (short bath) in a medium concentration, and up to 24 to 48 h (long bath) in a very low concentration. Proceed as follows.

(a) For a short bath, mix with water in a plastic watering can the amount of chemical required for the water volume to be treated. Lower the water level in the trough or circular tank by one-third to one-half. Let the water flow in again while spreading the previously mixed chemical over the entire surface area. If necessary, mix the water with a clean broom, an agitator or an aerator to evenly disperse the chemical within the whole water mass. Stop the water inflow once the water reaches its normal level. Treat for the required duration. Then drain two-thirds of the water while starting the water flow again.

(b) For a long bath, stop the water flowing into the tank or pond. Drain some water and reduce water volume to the acceptable minimum for the stock density and water temperature conditions. Determine water volume and required amount of chemical. Dilute this chemical amount at least 100 times, for example in several plastic buckets before application. Add this diluted solution to the tank or pond, spreading it as much as possible over the entire surface area and mixing it well with the pond water. Treat for the required duration. Then open the water flow and raise the water level back to normal. It necessary, drain again and refill.


Anticipated feed is used such like tetramycin composition.

Do’s and Don’ts (Since, Prevention is better than cure)

* Maintain optimum water quality
* Proper liming and fertilization
* Additional liming is beneficial in terms of disinfecting pond environment
* Proper stocking density
* Provision of balanced feed
* Quarterly sampling (look for external parasites, gill coloration and problems, red patches, ulcers, eye problems, scale or fin erosion, abnormal body shape and size, white cysts on body surface or gill surface, etc)
* Avoid foul smell in pond water
* Remove unwanted fish and snails
* Intermittent drying followed by disinfection of ponds between culture operations
* Stocking of quality or certified seeds in ponds
* If stocking yearlings, then collect the seed from already treated ponds with ectoparasiticides
* Stock the ponds when the water quality is good and pond having adequate fish food organisms
* Remove the infected or diseased fish during sampling and bring it to the notice of fish health workers
* Intermittent examination of water quality of the ponds during culture
* Use good quality water in hatcheries
* Remove aquatic weeds and avoid blooms
* Use always sun-dried nets before sampling
* Don’t use same net or equipment after being used in infected ponds
* Avoid entry of birds, dogs and other fish-eating animals to pond premises
* Use bamboo poles to look for laying of ectoparasite eggs to undertake immediate treatment, if noticed
* Dry the weeds, snails after removal from one pond
* Burn or chlorinate the dead fish at a distant place from the pond dykes
* Don’t discard dead fish on pond dykes
* Avoid plant leaves falling into the ponds
* Send the diseased fish samples (in live condition, if possible, in polythene water bags/frozen freshly dead fish) to the diagnostic laboratory for further testing and guidance.

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