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Fish Disease, Symptoms and Control


19 common Fish Diseases and their Symptoms and Control

Penaeus vannamei was introduced to my country from South America in the late 1980s. Fish health management is a term used in aquaculture to describe a management system designed to prevent fish diseases. Once fish become ill, it can be difficult to save them. Good fish health care starts with prevention rather than treatment. Prevention of fish diseases requires proper care for water quality, nutrition and sanitation. Without this foundation, it is impossible to prevent outbreaks of opportunistic diseases. Fish are also regularly washed with potential pathogens including bacteria, fungi and viruses. Even the use of sterilization technology (ie, ultraviolet sterilizers, ozonation) does not remove all potential pathogens from the environment. Poor water quality, poor nutrition, or a suppressed immune system combined with stressful conditions allow these bacteria to become infected. The drugs used to treat these diseases buy time for fish and help them to overcome the diseases that are available, but it is not a substitute for buying the right pet. Strong and other obvious advantages. In recent years, the culture of Penaeus vannamei has also developed rapidly in Asia and has broad prospects for development.


Diagram showing fish diseases prevention and control

1. Fish red body disease (taola virus disease)


Pathogen: Taola Virus


Popularity: i. After 2 days of drastic changes in temperature, the water temperature rises to 28 and is prone to disease

ii. The size of the diseased Fish is 6-9cm

iii. PH is above 9.0

iv. Ammonia nitrogen is above 0.5mg/L

v. The amount of influent water exchange exceeds 20% of the pool water, and the above conditions are prone to the disease, and the onset time is generally from April to October.


Symptoms of Taola Virus

The diseased Fish eat less or not, swim slowly on the water surface, and die after being pulled out of the water.

The disease has 3 different stages:

    1.     Acute stage

    2.     Transitional stage

    3.     Chronic stage

The symptoms of each stage are different. In the acute stage, the carapace of the diseased Fish was soft, the body color was light red, and the swimming feet and tail fan were obviously red.

The survivors of the acute phase of the diseased Fish are transferred to the chronic phase.

The diseased Fish that have not recovered from the serious illness will have black spots on the surface, the two tentacles and the tail fan will turn red, the gastrointestinal tract will be swollen, the hepatopancreas will be swollen and whitened, and the posterior abdominal muscles will be white.


Prevention of Taola Virus

(1) At the end of the year, after the Fish come out of the pond, clear the silt at the bottom of the pond, and thoroughly freeze and dry


(2) Before putting the seedlings, clean the pond or kill them all or quicklime thoroughly to disinfect the pond to kill the source of the disease


(3) Stocking high-health, virus-free Fish fry


(4) Probiotics are often used to adjust the water body during the breeding process to maintain good water quality and water environment, and the water level should be appropriately deepened in high temperature seasons


(5) When the rainstorm and the water level change too much, anti-stress drugs should be sprinkled in time to prevent stress reaction.



2. White spot syndrome of prawns


Pathogen: White spot syndrome virus and Vibrio


Pandemic: The disease is a widespread and harmful viral Fish disease in the Fish development stage.

If the water quality deteriorates and changes suddenly, and there is both Vibrio infection or the Fish's immune disease resistance is poor, the virus particles in the Fish will be reduced.

A large number of prawns will be replicated, resulting in symptoms.

Generally, 2-3 days after the onset of the Fish is seen, and a large number of Fish will die within a week at most.

It mainly damages Penaeus vannamei, Penaeus monodon, and Penaeus japonicus, etc. The broodstock with a small size of 2 cm and a larger size of 7-8 cm or larger are susceptible to this disease, and the mortality rate is as high as 90%. Onset time is March-November


Symptoms of White spot syndrome of prawns

The diseased Fish stopped eating, reacted slowly, bounced weakly, roamed the water surface or lay still at the bottom of the pool, and died soon.

The head carapace of the diseased Fish is easy to peel off, and some carapaces show obvious flower-like white spots, and the body surface is adhered to dirt.


3. Yellow head disease of prawns


Pathogen: Yellow Head Virus


Prevalence: The disease is most prone to the disease in juvenile Fish and Penaeus monodon that have been placed in seedlings for 50-70 days. The incidence rate can reach 100% within 3-5 days after infection, and the mortality rate is as high as 80-90%.

It is mainly horizontal transmission. Species (such as seagulls) are also one of the spreaders, and ponds with deteriorating water quality are also prone to this disease.


Symptoms of Yellow head disease of prawns

The diseased Fish have low vitality, loss of appetite, and irregular swimming on the surface of the water.

The carapace is yellow or sprouted, swollen, the gills turn pale yellow to brown, and the hepatopancreas becomes pale yellow.


4. Fish baculovirus disease


Pathogen: Baculovirus


Prevalence: This disease mainly harms Penaeus monodon and Penaeus japonicus.

It is prone to disease when the water temperature is high and the water quality is poor, and the mortality rate is high.


Symptoms of Fish baculovirus disease

 The diseased Fishs have slow response, poor appetite, dark body color, sessile ciliates, filamentous bacteria, epiphytic diatoms, etc. are attached to the gills and body surface, and the hepatopancreas turns white, shrinks, grows slowly, anorexia, and does not take off. shell until death.


5. Hepatopancreatic parvovirus disease


Pathogen: Hepatopancreatic parvovirus


Pandemic: This disease mainly harms Chinese prawns, Penaeus merguis, and Penaeus monodon, which can also be infected.

The disease is severe in the larval stage, and the mortality rate is generally 50%-90%. There is Poisonous and latent infection.


Symptoms of Hepatopancreatic parvovirus disease

The hepatopancreas becomes white, atrophied, and necrotic, the carapace is soft, with black spots, and the abdominal muscles become white.

Infographics on fish diseases and symptoms


6. Infectious subcutaneous and hematopoietic necrosis of Fish


Pathogen: Infectious subcutaneous and hematopoietic tissue necrosis virus.


Popular: This disease is a disease of Penaeus monodon and Penaeus japonicus. It is a disease of juvenile and adult Fish. It dies during or after molting, and the larvae and larvae are not harmed.

This disease does not occur in Fish nurseries. It is prone to disease when the water temperature is high and the water quality is poor.


Symptoms of Infectious subcutaneous and hematopoietic necrosis of Fish

The carapace of the acutely sick Fish turns white or has brown patches, the muscles are cloudy and opaque and often float or hang on the surface of the water, the swimming is slow, anorexia, the fish body is turned over, and the abdomen is upward.

Chronic disease Fish with deformed and distorted forehead swords, with dirt on the body surface and gills, slow growth, abnormal swimming, slow swimming on the water surface or motionless, abdomen upward, sinking to the bottom and then floating and sinking again and again.


7. Fish red leg disease


Pathogen: Ibrio parahaemolyticus


Epidemic: This disease mainly harms Penaeus monodon, Penaeus vannamei, and Penaeus japonicus in the aquaculture stage. %, or even all dead.

It is popular when the water temperature is 25-30 , and it occurs most frequently from June to October, and can last until November.

Fish ponds with poor water quality are most prone to disease.


Symptoms of Fish red leg disease

The diseased Fish swim slowly by the pool or lie on the bottom, the appendages turn red, especially the swimming feet are red, the carapace and gill area are yellow, and they are anorexia.


8. Fish muscle necrosis (white turbidity) disease


Pathogen: Vibrio


Prevalence: This disease is prevalent when the water temperature is high, and fish ponds with poor water quality and low dissolved oxygen in the water are most prone to this disease.


Symptoms of Fish muscle necrosis (white turbidity) disease

 The diseased Fish has white spots on the abdomen (especially 4-6 sections), or the entire abdomen is white, and the muscles from the abdomen to the tail are white.

The behavior is abnormal, and the performance is restless. It often moves on the water surface and jumps out of the water.


9. Fish rotten eye disease


Pathogen: Non-group 01 Vibrio cholerae


Popular: Fish ponds in the Yanhai area have poor water quality and too much organic matter, which is caused by traumatic infection of Fish. 

The onset season is March-October, with the highest in August.

The infection rate is 30-50% as high as 90%, which seriously affects the growth and the mortality rate is not high.

Overwintering broodstock can also get sick.


Symptoms of Fish rotten eye disease

The eyes of the newly sick Fish are swollen, the color of the cornea changes from black to brown, and then rots into a white membrane. 

Severely ill Fish eyes are all rotten, only the eye stalks are left, and the muscles of the whole body are white.

Sick Fish are sluggish, lying on the edge of the pool or spinning around on the water surface.


10. Fish gill rot disease


Pathogen: Vibrio or other bacilli


Epidemic: The disease is widespread and occurs throughout the breeding cycle. The incidence is high and the harm is great. The disease is more likely to break out when the water quality and bottom of Fish ponds deteriorate.


Symptoms of Fish gill rot disease

The gill filaments of the diseased Fish are gray or black, swollen and brittle, festering from the tip, and the festering and necrotic part shrinks or falls off.

Sick Fish float on the water surface, swim slowly, unresponsive, anorexia, and finally die.


11. Fish yellow gill disease


Pathogen: Aeromonas or Vibrio


Prevalence: This disease is prone to outbreaks when the nitrite content is high due to uneven stratification of the upper and lower salinity of the water body, or sudden changes in pH value after rainy days.

 The incidence is high, and if not controlled in time, it can cause gill rot disease.


Symptoms of Fish yellow gill disease

The lower edge of the carapace of the diseased Fish is pale yellow near the feet, and the gill filaments are edematous, yellow, and prone to rotten gills over time.


12. Fish brown spot disease (crustacea canker)


Pathogen: Vibrio, Aeromonas, Pseudomonas, Myxobacteria, Benedictine


Popular: This disease is caused by inadvertent operation, injury of Fish, malnutrition, or high levels of toxic chemicals (such as heavy metals) in the water environment and poor water quality in Fish ponds.


Symptoms of Fish brown spot disease (crustacea canker)

There are black ulcer spots on the carapace and appendages of the diseased Fish.

The edge of the ulcer is white, and the center of the ulcer is depressed.

severe cases, the tissue under the carapace can be eroded.


13. Fish enteritis


Pathogen: Poisoning caused by bacteria or ingestion of certain algae.


Prevalence: When the water temperature is high (25-30), Fish ponds or Fish malnutrition after algal aging and death are prone to this disease.


Symptoms of Fish enteritis

The digestive tract of the sick Fish is red, swollen and inelastic, and some stomachs are blood red.


14. Fluorescent disease of Fish


Pathogen:Vibrio luminous, curved short rod-shaped


Prevalence: The disease occurs from flea-like larvae to adult Fish in nursery farms.

Mysid Fish and larvae stage, larvae are from May to July, the water temperature is 28-30 on sunny days, and the water contains a lot of organic matter, and pathogenic bacteria multiply in large numbers.

The fatality rate is high, and it is difficult to control, 80-90% of the larvae die within a few days, and in severe cases, the larvae and the Artemia all glow, and the death can reach 100% within 3-5 days.

The incidence of adult Fish is mostly in the middle and late stages of aquaculture, and the high temperature season from July to September when there is a lot of organic matter in fish ponds, the incidence rate is low, but the mortality rate is higher when it is complicated with red limb disease, filamentous bacterial disease, and ciliate disease.


Symptoms of Fluorescent disease of Fish

In the early stage of the disease, the gills, carapace, and abdominal muscles of the Fish fluoresced in the dark.

The diseased Fish broke off the tentacles, reduced or stopped feeding, and swam slowly around the pool with unresponsiveness.


15. The Fish pond glows at night


Pathogen: Noctiluca, Luminous bacteria, Luminous dinoflagellates, etc.


Prevalence: This disease is most likely to occur in fish ponds with thin and poor water quality.


Symptoms of the Fish pond glows at night

On a moonless night, when you stir the pool water with your hands, obvious luminescence can be seen.

When there are too many noctilucent worms, luminous bacteria, and luminous dinoflagellates in the fish pond, they will consume a lot of oxygen, causing the fish to have difficulty breathing, and the light in the water will cause the fish to panic, lose appetite, and reduce disease resistance.


16. Sessile ciliate disease of prawns


Pathogen: polycondensed worms, branch worms, single condensed worms, bell-shaped worms, etc.


Popular: This kind of insect grows and breeds in the dirty water of Fish ponds with a lot of organic matter, low pH and poor running water.


Symptoms of Sessile ciliate disease of prawns

 The swimming body is attached to the body surface, appendages, and gills of eggs, larvae, and Fish.

When there are few insects, there is no obvious symptom.

There is a layer of gray-black villi on the surface, and the gills are also covered with worms, filamentous bacteria, protozoa, unicellular algae, organic particles and other dirt.

The antennae, legs and gill filaments are taken to make water-immersed films.

The worms can be seen under a low-power microscope.

The diseased Fish floats on the water surface in the morning, and the response is slow, no feeding or molting, and growth is stagnant, which mainly affects the respiration of the Fish.


17. Filamentous algae attachment disease of Fish


Pathogen: algae such as prolifera, bristle algae, water cloud, etc.


Popular: This disease is prone to occur in Fish ponds with high water temperature and thin water quality.


Symptoms of Filamentous algae attachment disease of Fish

There are clusters of epiphytic filamentous algae on the body surface of the diseased fish.

In severe cases, the entire body surface of the diseased fish, including the eyeball, is covered with algae, and the entire body of the fish is dark green.


18. Soft shell disease of prawns


Causes: Long-term nutritional imbalance, excessive changes in salinity of fish pond water, and insufficient or unbalanced calcium and phosphorus


Prevalence: The disease is more likely to break out after a rainy day due to the uneven salinity of the upper and lower water bodies.


Symptoms of Soft shell disease of prawns

The carapace of the diseased Fish is soft for a long time. In severe cases, the Fish shell will be wrinkled and the lesions of the rotten shell will appear.


19. Fish Stealing Death Disease


Cause: Due to the serious deterioration of the water quality and bottom of the Fish pond, especially the high nitrite and ammonia nitrogen, and the severe hypoxia at the bottom.


Epidemic: This disease is most likely to occur when the water quality and bottom of the intensive pond deteriorate seriously


Symptoms of Fish Stealing Death Disease

In the early morning, some prawns are seen crawling to the side, and they often swim slowly on the water surface.

The dead prawns can be picked up with a net at the bottom of the aerator, and sometimes dead prawns can be seen in the observation net.


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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