UNIT -4

TOPIC – SHRIMP DISEASES

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INTRODUCTION:

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• After L. vannamei was introduced to Asia, shrimp production increased significantly. L. vannamei became the most important shrimp species in terms of aquaculture production, it is more than 70%.

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• The other important species are Penaaeus monodon, Macrobrachium rossenbergii, P. chinensis, P. merguiensis, P. japonicas, and P. indcus.

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• The increase in shrimp production has resulted by intensification of production, which is directly linked with an increased incidence of diseases.

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• Causes of infectious diseases include:

1.Viruses � 2.Bacteria � 3.Fungi � 4.Parasites

5.Non-Infectious

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VIRAL DISEASES

1.MONODON BACULO VIRUS-MBV:

ETIOLOGICAL AGENT

• MBV- type or PmSNPV is a type A occluded mondon baculovirus

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CLINICAL SIGNS :

• Lethargy, anorexia,poor feeding,dark colouration and reduced growthrate.
• Infectedshrimps are often associated with fouling of gills and appendages by cilates such as Zoothamnium spp.and vorticle spp .
• Acute infection leads to loss of epithelial cells of hepatopancreas

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PREVENTION:

• Prevention is only by using viral free brood stocks.
• Eggs and nauplii are to be throughly washed before transferring them to rearing tanks.

2.HEPATOPANCREATIC PARVOLIKE VIRUS (HPV) DISEASE.

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ETIOLOGICAL AGENTS

• HPV is caused by a small parvo - like virus 22-24nm in diameter

CLINICAL SIGNS

• Reduced feeding, poor growth rate, body surface and gill fouling with ciliates and occasional opacity of abdominal muscles.
• Severe infections may include a whitish and atrophied hepatopancreas, anorexia and reduced preening activity.

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PREVENTION AND CONTROL

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• No information is available on the prevention and control procedures for HPV infection.
• However screening the PLs before stocking shrimp by routine histology or the Giemsa impression smear is recommended.
• Losses may be occur due to the increased occurrence of surface and gill fouling organisms and secondary infections by opportunistic Vibrio spp.

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TREATMENT

• No treatment is available for HPV infection.

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3.INFECTIOUS HEPATOPANCREA AND LYMPHOID ORGAN NECROSIS (IHLN)

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ETIOLOGICAL AGENTS :

• The primary cause of the disease is attributed to viral etiology.

CLINICAL SIGNS:

• Light pinkish to yellowish discolouration of the cephalothorax region.
• Often fouling by ciliate protozoan zoothamnium seen.
• Blackened and necrotic hepatopancreas.
• Secondary bacterial infection from bacteria such as Vibrio alginolyticus seen.

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TREATMENT :

• No treatment is available for IHLN infection.

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PREVENTION AND CONTROL :

• Keep the physico chemical condition of pond environment within acceptable levels .
• To avoid bacterial and viral pathogen entering from outside, closed could be useful in Prevention of IHLN disease.

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4.YELLOW HEAD DISEASE – (YHV)

ETIOLOGICAL AGENTS

• YELLOW HEAD VIRUS is a 35rRNA, rod shaped enveloped virus with two rounded ends.

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CLINICAL SIGNS

• The affected shrimps shows a marked reduction in food consumption
• Following this a few monbound shrimp will appear swimming slowly near the surface of the pond dike and remain motionless.
• The animals have pale bodies a swollen cephalothorax with a light yellow to yellowish hepatopancreas and gills.
• A high mortality rate may reach 100%of affected populations within 3-5days from the onset of disease.

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TREATMENT

• No treatment is available for YHV infection.

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PREVENTION

• The reliable method to prevent the occurrence of YHD is possibly through avoidance, such as careful selection of postlarvae, reduction or elimination of horizontal transmission including carriers,disinfection of contaminated ponds or equipment with 30ppm and chlorine providing shrimp with good water quality and proper nutrition.

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5.WHITE SPOT DISEASE:

ETHIOLOGICAL AGENTS:

• The disease is caused by the dsDNA virus, Systemic Ectodermal and Mesodermal Baculovirus (SEMBV)

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CLINICAL SIGNS :

• Clinically affected shrimp were first seen to swim to the water surface and congregate at the pond dikes.

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• Typical clinical signs include white spots or patches, 1-2mm in diameter on the inside of the shell and carapace accompanied by reddish discolouration of the body.

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• SEMBV is able to cause epizzotics of 5-10days duration with

mortality rate from 40%to100

TREATMENT

• No treatment is available for SEMBV infection.

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DIAGNOSIS PROCEDURE

• The diagnosis procedure of SEMBV
• Infection is based on the appearance of the intranuclear hypertrophy in stained histological sections and the presence of virus particles in the nucleus of the infected cells observed under the electron microscope.

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• PCRtechnique is recently used to detect SEMBV in shrimp larval and other stages, including broodstock and subclinical virus carriers.

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PRECAUTIONARY MEASURES :

• It is important that farmers check if the stock contains WSSV and to destroy the stock as soon as it is proven to be infected.
• The water quality must be kept in check, regularly cleaned, and monitored for possible infective sources.

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BACTERIAL DISEASES

1.VIBRIOSIS :

ETIOLOGICAL AGENTS

• Vibrio vulnificus, V. parahaemolyticus, V.

alginolyticus, V.anguillarum, V.damsella,

V.fluvialis and V. mimicus

CLINICAL SIGNS

• High mortality rates particularly in young

juveniles shrimp.

• Moribund shrimp with corkscrew swimming

behaviour appear at edge of pond.

• Reddish discolouration of juvenile shrimp.

EXTERNAL FOULING :

• Black spots chronic soft shelling.

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• Disinfection of intake water i. eformalin 100

200ppm.

• Antimicrobial preparation application through feeds (oxolinic acid) 0.6ppm and Sarafloxacin 5mg/kg.

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PREVENTION AND CONTROL

• Proper pond and water management and

utilisation of reservoir for intake water.

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2.LUMINOUS VIBROSIS:�

• One of the major disease problems in grow-out shrimp culture is the Luminous Vibriosis.
• This disease, caused by the bacteria Vibrio harveyi, V.splendidus and other luminescent vibrios, affects the eggs, larvae, post

larvae and juveniles of the shrimp.

• Vibriosis weakens the larvae and juveniles.
• Larvae become opaque-white while the juveniles have discolored portions on the body.

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• As the common name of the disease suggests, the larvae glow green when in total darkness.
• Luminous Vibriosis can be deadly to the shrimp and has potential to kill up to 100% of the shrimp population.

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PREVENTION

• To prevent this, it is best to monitor the shrimp during their early stages and to check the bacteria present via water sample tests regularly.
• It is also advisable to create microbial diversity in the water to competitively exclude the pathogens by using probiotics.

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FUNGAL DISEASES

1.LARVAL MYCOSIS

ETIOLOGICAL AGENTS

• Filamentous Fungi of genus Lagenidium spp. and other filamentous fungi such as sirolpidium spp and Haliphthoros spp.

CLINICAL SIGNS

• Eggs and larvae are weak and appear whitish. Mortilities may reach 100%within two days. Fungal mycelium replaces the larval tissues and ramities into all parts of the body and protrudes out of the body and developes into sporangia

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PREVENTION AND CONTROL

• General hatchery management practices such as use of UV sterilized and filtered seawater, adequate water exchange etc.. must be strictly followed.
• Rearing water, equipment used in the hatchery and all hatchery facilities must be throughly disinfected before retarting the hatchery operation

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2.BLACK GILL DISEASE :

ETIOLOGICAL AGENTS

• It is caused by fusarium spp..

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CLINICAL SIGNS

• Brownish to blackish discolouration on the gills of juveniles shrimp.

TREATMENT

• No treatment is available for fungal infestation without harming the shrimp.

PREVENTION AND CONTROL

• No information on Prevention and control.
• However, good management of the pond bottom and prevention of the entry of wild crustaceans into the pond which may carry pathogen can be effective control practices.

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PARASITIC DISEASE

1.MICROSPORIDOSIS:�

ETIOLOGICAL AGENTS

• Microsporidia such as Thelohania spp. Nosema spp. and pleistophora spp.

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CLINICAL SIGNS

• Infected shrimps appear opaque and cooked

Gradual and low levels of moralities are observed.

Microsporidia invade and replace gill, muscle, heart, gonads and hepatopancreas, and cause necrosis in these regions.

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PREVENTION AND CONTROL

• Maintainance of good sanitary conditions at the pond bottom and the overall pond area.

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2.WHITE FECES DISEASE:

• A common symptom of White Feces Disease (WFD) in shrimp is the change in color of the gut.
• Compared to a normal shrimp, the gut is pale white instead of a darkish brown color.
• The feces excreted by the shrimp is also more buoyant than normal as the white excrement floats to the surface of the pond.
• The exoskeleton of infected shrimp become loose, and there is a dark discoloration on the gills.
• Studies show that shrimp with WFD lose appetite and can even reach up to 60% mortality.

• White Feces Disease is associated with many environmental factors such as

1.Poor water quality.

2.Pond bottom sludge accumulation,

3.Plankton blooms.

4.Some growing practices such as

5.High stocking densities and

6.Bad feed management have also been connected to the disease.

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PREVENTION:

• Since the exact cause of WFD is still unknown, it is best to follow biosecurity and water management best practices to reduce the risk of its occurrence.

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NON-INFECTIOUS DISEASES

1.SOFT SHELL SYNDROME :

ETIOLOGICAL AGENTS

• The exact cause of soft shell syndrome is not know.
• However low saline condition in the culture pond and deterioration of pond bottom condition are some physico chemical factors that causes this disease.
• Shrimps fed with low protein diet contamination through agricultural run off, high soil PH, low water phosphate and low organic matter in soil all have an impact on soft shell disease.

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CLINICAL SIGNS

• Shrimps are weak, usually off feed have a loose thin exoskeleton. Rostrum is stiff as healthy shrimps. Wavy undulating intestine is clearly visible.

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PREVENTION:

• Low stocking density feeding with high quality feed and frequent water exchange are likely to reduce the recurrence of the disease.

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2.MUSCLE NECROSIS

ETHIOLOGICAL AGENTS

• Muscle necrosis in shrimp is caused by temperature and salinity shock, low oxygen levels, overcrowding, rough handling and severe gill fouling.

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CLINICAL SIGNS

• Affected shrimp show opaque white areas on the abdomen blackening on the edges of the uropod followed by erosion and liquid filled boils at the tip of uropods in advanced stages, Wood grain appearance of abdominal muscle in postlarvae

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EFFECT ON HOST

• There is a gradual death of cells of affected parts leading to erosion especially in the tail. This may then serve as portal of entry for secondary Systemic bacterial infection.

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PREVENTION

• Reduce stocking density and improve water quality by daily water change (5-10%)

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THANK YOU