White spot disease (WSSV) in shrimp: signs and prevention

White spot disease, caused by WSSV (White Spot Syndrome Virus), is one of the most dangerous diseases in shrimp farming. The virus spreads very fast, and shrimp in almost an entire pond can die within just 3–10 days after the first signs appear.

Signs of white spot disease

• Round white spots, 0.5–2 mm in diameter, appear under the carapace (cephalothorax shell), then spread to the abdominal segments. Peel the shell and hold it against the light to see them clearly.
• Shrimp suddenly eat less, swim lethargically, gather at the pond edge or come up to the surface.
• Some shrimp have a pink or light red body.
• Mortality rises quickly day by day, starting with the larger, stronger shrimp.

Note: white spots can also be caused by bacteria or by high-alkalinity water depositing minerals on the shell. To be sure, farmers should carry out PCR testing.

Conditions that trigger outbreaks

• Sudden temperature changes, especially during seasonal transitions, prolonged heavy rain, or when water temperature falls below 28°C.
• Intake water contaminated with virus from surrounding diseased ponds.
• Wild crustaceans (crabs, fiddler crabs, small shrimp, copepods), birds and equipment carrying the pathogen into the pond.
• Postlarvae carrying the virus from the hatchery.

Preventing white spot disease

There is currently no cure for white spot disease. Prevention based on biosecurity principles is the only approach.

• Select disease-free postlarvae with a PCR-negative result for WSSV.
• Settle, filter and disinfect water before supplying it to grow-out ponds; use disinfectant products such as BEN IQ or IODINE 99 as instructed; wait 2–3 days after disinfection before building water colour and adding probiotics.
• Install crab-proof fencing and bird-deterrent lines, and use separate equipment for each pond.
• Keep temperature and the environment stable: raise the water level and cover with netting in the cold or rainy season; keep algal density and pH stable, for example with SUPER VIDAL, which supports algae and pH stabilisation, used per the label.
• Boost resistance in bad weather: add BETA 1.3, vitamin C such as VITA C (pond application) or NB C SORMIN to reduce stress.

What to do when a pond is infected with white spot

1. Immediately inform the local veterinary officer and neighbouring farms.
2. Do not discharge water from the diseased pond into the environment. Inactivate the virus in the pond according to veterinary authority guidance before discharging.
3. If the shrimp have reached marketable size, consider an early harvest.
4. After the disease crop, prepare the pond thoroughly, dry the bottom, eliminate crustaceans and let the pond rest before the next crop.