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Fish Disease, Symptoms and Control


19 common Fish Diseases and their Symptoms and Control

In the late 1980s, Penaeus vannamei was imported from South America to my nation. In aquaculture, the term "fish health management" refers to a management strategy intended to stop fish infections. Fish that grow sick can be challenging to save. Instead of beginning with therapy, good fish health care starts with prevention. The right water quality, diet, and sanitation practises are necessary for the prevention of fish infections. Opportunistic disease epidemics cannot be stopped without this basis. Fish are routinely cleaned with potentially harmful bacteria, fungus, and viruses. Even the use of sterilisation technology (such as ozonation and ultraviolet sterilisers) cannot completely rid the environment of possible microorganisms. These bacteria can become infected when there are stressful circumstances present as well as poor water quality, inadequate diet, or a depressed immune system. The medications used to treat these illnesses provide fish more time and aid in their ability to overcome the illnesses that are present, but they are not a replacement for choosing the best pet. Strong and other clear benefits. Penaeus vannamei's culture has recently experienced rapid development in Asia and has a wide range of development opportunities.


Diagram showing fish diseases prevention and control


1. Red body sickness in fish (taola virus disease)

Taola virus, a pathogen

Popularity: i. The water temperature rises to 28°C after 2 days of abrupt temperature swings and is contagious.

ii. The sick fish measure 6–9 cm in length.


iii. A PH of over 9.0.


iv. Ammonia nitrogen is greater than 0.5 mg/L

The disease typically manifests between the months of April and October when the influent water exchange amount exceeds 20% of the pool water.


Virus Taola symptoms

When removed out of the water, the sick fish die after eating less or not at all, swimming slowly on the surface.


There are three stages to the illness:

1. Intensive stage

2. Stage of transition

3. Prolonged stage 

Each stage's symptoms are unique. The infected fish's carapace was soft, its body colour was a light red, and its swimming fins and tail fan were clearly red during the acute stage.

The ill fish's acute phase survivors are moved to the chronic phase.

The gastrointestinal tract will be bloated, the hepatopancreas will be swollen and whitened, the posterior abdominal muscles will be white, and the diseased Fish will have black spots on the surface. They will also have reddened tentacles and tail fans.

(1) At the end of the year, when the fish have left the pond, remove the silt from the bottom of the pond and completely freeze and dry it.

(2) Thoroughly cleanse the pond with quicklime to kill the disease's cause before putting the seedlings in it. Alternatively, you can kill them all.

(3) Stocking virus-free, high-quality fish fry

(4) Probiotics are frequently used to modify the water body during the breeding process in order to preserve good water quality and water environment. In high temperature seasons, the water level should also be adequately deepened.

(5) Anti-stress medications should be administered promptly to avoid a stress reaction when the downpour and the water level fluctuate too drastically.


2. Prawns with the white spot syndroms

White spot syndrome virus and Vibrio are pathogens.

Pandemic: The condition is a contagious viral fish sickness that is now affecting the growth of the fish.

The amount of virus particles in the fish will decrease if the water quality abruptly declines and changes, and if there is also a Vibrio infection or a weak immune system.

The symptoms will be caused by the replication of a huge number of prawns.


Fish usually appear 2-3 days after their commencement, and a significant portion of them will perish within a week at most.


Penaeus vannamei, Penaeus monodon, and Penaeus japonicus, among others, are primarily hurt. The death rate for this disease is as high as 90% for broodstock with small sizes of 2 cm and greater sizes of 7-8 cm or larger. onset is from March and November.


White Spot Syndrome in Prawns Symptoms

The sick fish stopped consuming food, moved slowly, bounced clumsily, roved the water's surface, or remained motionless at the bottom of the pool, and soon perished.

The sick person's head carapace Fish has a body surface that is stuck to soil and some carapaces have prominent flower-like white markings.


3. Prawns with yellow head sickness

Virus called Yellow Head

Prevalence: Juvenile Fish and Penaeus monodon that have been kept in seedlings for 50–70 days are particularly susceptible to the disease. Within 3-5 days of infection, the incidence rate can reach 100%, and the fatality rate can reach 80–90%.

Mostly horizontal transmission is used. The disease can also spread through species (like seagulls), and it is more likely to occur in ponds with poor water quality.

Prawns with Yellow Head Disease symptoms

Low vitality, loss of appetite, and erratic swimming on the water's surface are all symptoms of ill fish.

The hepatopancreas turns pale yellow, the carapace is yellow or sprouted, enlarged, and the gills change colour from pale yellow to brown.


4. The fish baculovirus illness

Viral baculovirus

Prevalence: Penaeus monodon and Penaeus japonicus are the principal victims of this disease.


When the water temperature is high, the water is of low quality, and the mortality rate is high, it is susceptible to disease.


Fish baculovirus illness symptoms

Sessile ciliates, filamentous bacteria, epiphytic diatoms, etc. are adhered to the gills and body surface in unhealthy fish, and the hepatopancreas turns white, shrinks, grows slowly, anorexic, and remains inside the shell until death.


5. Hepatitis caused by the parvovirus



Hepatitis-pancreatic parvovirus 

Chinese prawns, Penaeus merguis, and Penaeus monodon, which are also susceptible to infection, are the primary victims of this pandemic.


The death rate is often between 50% and 90% when the disease is in its advanced larval stage. Poisonousness and latent infection exist.

Hepatopancreatic parvovirus illness symptoms

The carapace is fragile and spotted with black dots, the abdominal muscles turn white, and the hepatopancreas turns white, atrophied, and necrotic.

Infographics on fish diseases and symptoms


6. Infectious subcutaneous and hematopoietic necrosis of Fish


Subcutaneous and hematopoietic tissue necrosis virus, an infectious agent.


Popular: Penaeus monodon and Penaeus japonicus are susceptible to this illness. It affects both young and adult fish. It perishes during or following moulting, with no harm coming to the larvae or larvae.


Fish nurseries are not affected by this illness. When the water is dirty and the temperature is high, it is more prone to illness.


Symptoms of Fish Hematopoietic and Subcutaneous Infection

Acutely ill fish have a carapace that goes white or develops brown spots, foggy, opaque muscles that frequently float or hang on the surface of the water, slow swimming, anorexia, a turned-over body, and an upward-facing abdomen.


Chronic illness: Fish with malformed and misaligned forehead swords, filth on the body surface and gills, slow growth, aberrant swimming, slow swimming on the water surface or immobile, abdomen upward, sinking to the bottom and then floating and sinking repeatedly are among the more unusual fish.



7. Red leg illness in fish


Ibrio parahaemolyticus, the pathogen

Penaeus monodon, Penaeus vannamei, and Penaeus japonicus are primarily affected by this illness in the aquaculture stage, and in some cases, they are completely killed.

It is popular when the water is between 25 and 30 °C, and it usually lasts from June through October, however it might go as late as November.

Disease is most likely to occur in fish ponds with low water quality.

Fish red leg illness symptoms

the ailing Fish with anorexia move slowly at the water's edge or lie on the bottom. The appendages, particularly the swimming feet, turn red, and the carapace and gill region turn yellow.



8. White turbidity sickness in fish muscle


Bacteria: Vibrio

Prevalence: This disease is most common in fish ponds with poor water quality and low levels of dissolved oxygen in the water. It is also more common when the water temperature is high.


Fish muscle necrosis (white turbidity) illness symptoms

The white blotches or dots all over the abdomen, as well as the muscles from the abdomen to the tail, are characteristics of a sick fish.

Both the behaviour and the performance are strange. It frequently jumps out of the water and moves on the water's surface.


9. Disease of the fish's eyes


Vibrio cholerae, a non-group 01 pathogen

Popular: Due to fish trauma infections, the water quality and amount of organic matter in the fish ponds in the Yanhai area are low.


The onset season runs from March through October, with August being the peak.


The infection incidence is 30–50% up to 90%, which negatively impacts growth and has a low fatality rate.

Additionally, sickly broodstock can overwinter.


Fish rotting eye disease signs

When a fish first becomes ill, its eyes swell, its cornea turns from black to brown, and eventually it rots into a white membrane.


seriously unwell All of the fish's eyes are rotten; all that's left are the eye stalks, and the body's muscles are all white.


Fish that are ill are lethargic, lying on the side of the pool or circling the water.


10. Fish gill rot disease


Vibrio or other bacilli are the pathogen

Epidemic: The illness is pervasive and affects breeding animals at all times. The frequency is high and the damage is substantial. When fish ponds' bottoms and water quality deteriorate, the disease is more prone to spread.


Fish gill rot disease signs

the sick fish's damaged gill filaments Fish are fragile, bloated, and grey or black in colour. The tip of the fish is rotting and necrotic, and it shrinks or falls off.

Sick fish float on the surface of the water, swim slowly, become unresponsive, develop anorexia, and eventually perish.


11. Yellow gill illness in fish


Aeromonas or Vibrio as a pathogen

Prevalence: This disease is prone to outbreaks when the nitrite content is high because the upper and lower salinities of the water body are unevenly stratified, or when the pH value suddenly changes after wet days.


The likelihood is high, and if it is not stopped in time, gill rot illness may result.


Fish yellow gill disease symptoms

The edematous, yellow, and susceptible to developing rotten gills over time gill filaments are present at the lower edge of the diseased fish's carapace close to its feet.



12. Brown spot sickness in fish (crustacea canker)


Aeromonas, Pseudomonas, Myxobacteria and Benedictine pathogens

Popular: Poor water quality in fish ponds, unintentional operation, fish damage, starvation, or excessive amounts of harmful substances (such heavy metals) in the environment are the main causes of this disease.


Fish brown spot sickness signs (crustacea canker)

The infected Fish's carapace and appendages have black ulcer spots on them.

The ulcer's centre is depressed, and the ulcer's margin is white.

In extreme circumstances, the tissue underneath the carapace may deteriorate.



13. Fish-borne illness

Pathogen: A bacterium or specific types of algae that can cause poisoning.

Prevalence: This disease is more common in fish ponds or fish starvation following algal ageing and mortality when the water temperature is high (25–30°C).


Fish enteritis symptoms

The ill Fish's digestive tract is red, bloated, and inelastic, and some of their stomachs are blood red.


14. Fish fluorescent illness

Vibrio, a bright, short, rod-shaped pathogen

Prevalence: In fish nursery farms, the illness spreads from flea-like larvae to adult fish.


Mysid Fish and larvae are present throughout the larval stage, which lasts from May to July. On sunny days, the water temperature ranges between 28 and 30 °C, there is a lot of organic matter in the water, and pathogenic bacteria multiply rapidly.


80–90% of the larvae perish within a few days, and in severe cases, both the larvae and the Artemia glow, increasing the mortality rate to 100% within 3-5 days. The mortality rate is high and difficult to regulate.


occurrence of adult The majority of fish are in the middle and late stages of aquaculture. Red limb disease, filamentous bacterial disease, and ciliate disease are the most common complications during the high temperature season from July to September when there is a lot of organic debris in fish ponds.


Fish fluorescent illness symptoms

The Fish's gills, carapace, and abdominal muscles fluoresced in the dark at the early stages of the illness.


The sick fish snapped off their tentacles, decreased or stopped feeding, and moved slowly around the pool while seeming unresponsive.


15. At night, the fish pond shines

Pathogens include Noctiluca, Luminous dinoflagellates, Luminous bacteria, etc.

Prevalence: Fish ponds with thin and bad water quality are most likely to have this disease.

Fish pond sparkles at night symptoms

When you stir the pool water with your hands on a moonless night, you can clearly detect radiance.


The fish will have trouble breathing if there are too many noctilucent worms, luminescent bacteria, and luminescent dinoflagellates in the fish pond. Additionally, the light in the water will make the fish nervous, make them lose interest in food, and make them less resistant to disease.


16. Prawns with sessile ciliate illness

Pathogens include bell-shaped worms, single condensed worms, branch worms, and polycondensed worms.

Popular: This type of insect thrives and reproduces in the unclean fish pond water that has high levels of organic matter, a low pH, and bad running water.


symptoms of prawns with sessile ciliate illness

The surface, appendages, and gills of eggs, larvae, and fish are linked to the swimming body.


There is no evident sign when there are not many insects.


The surface is covered in a coating of gray-black villi, and worms, filamentous bacteria, protozoa, unicellular algae, organic particles, and other debris are present on the gills.


Making water-immersed films requires the removal of the antennae, legs, and gill filaments.


With the use of a low-power microscope, the worms can be seen.


The sick fish hovers on the surface of the water in the morning, and it responds slowly, does not feed or moult, and grows slowly, which primarily affects the fish's respiration.


17. Fish with Filamentous Algae Attachment Disease

Algae pathogens include prolifera, bristle algae, and water clouds.

Popular: Fish ponds with high water temperatures and poor water quality are prone to this sickness.


Fish sickness caused by filamentous algae attachment symptoms

On the body surface of the sick fish, epiphytic filamentous algae are grouped together.

With severe cases, the infected fish's entire body surface, including the eyeball, is covered in algae, turning its entire body a dark green colour.


18. Prawns that have soft shell disease

Long-term nutritional imbalance, significant salinity variations in fish pond water, and a deficiency or an imbalance in calcium and phosphorus are the causes.

Due to the unequal salinity of the higher and lower water bodies, the disease is more prone to spread after a rainy day.


Symptoms of prawns with soft shell disease

Long-lasting softness is present in the diseased fish's carapace. When the condition is severe, the fish's shell may wrinkle and lesions from the decaying shell will show.


19. Disease that Causes Fish to Die

Cause: As a result of the Fish Pond's bottom and water quality seriously declining, particularly due to high levels of nitrite and ammonia nitrogen and severe hypoxia at the bottom.

Epidemic: When the intensive pond's bottom and water quality drastically deteriorate, this disease is most prone to spread.


Fish Stealing Death Disease signs and symptoms

Prawns are frequently spotted swimming gently on the water's surface in the early morning hours.


Dead prawns can occasionally be observed in the observation net as well as collected up with a net at the aerator's bottom.


Author's Bio

Doctor Shawna Reason, Virologist
Dr. Shawna Reason
Name: Shawna Reason

Education: MBBS, MD

Occupation: Medical Doctor / Virologist 

Specialization: Medical Science, Micro Biology / Virology, Natural Treatment

Experience: 15 Years as a Medical Practitioner

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