WSSV, Emergency harvest and falling shrimp prices: Are we preparing too late?

By Dr. Wiphada Mitbumrung, Ph.D. Applied Marine Biosciences — Thu Aug 27 2026

Shrimp farmers in Andhra Pradesh are once again facing a difficult combination: disease pressure and weak market prices.

A local report published by Andhra Jyothy on 23 August 2026 described a serious situation around Mudinepalli and the surrounding aquaculture belt. According to the report, changing weather conditions, oxygen problems and viral disease were causing shrimp mortality, forcing many farmers to harvest their ponds urgently. The report estimated that harvesting had taken place in around 30% of the farming area within two days, with many affected shrimp still only around 140 to 160 count. At this size, farmers receive a much lower price and may not recover their production costs. This comes at a time when Andhra Pradesh farmers are already under market pressure. On 12 August, the Government of India reported that the Andhra Pradesh government had identified declining market prices and increasing production costs among the major problems faced by aquaculture farmers. When large numbers of ponds are harvested early, more small-size shrimp enter the market within a short period. This can create additional supply pressure at exactly the time farmers are already struggling with prices.

But the real issue begins inside the pond.

Earlier in August, The New Indian Express reported a sharp increase in White Spot Syndrome Virus (WSSV) cases in Nellore, together with Vibrio and white-gut problems. Farmers reported premature harvesting as feeding declined, growth slowed and mortality increased. Fisheries officials also highlighted high temperature, low dissolved oxygen and environmental stress as contributing factors to disease problems. WSSV is particularly dangerous because a shrimp pond can appear normal even when the virus is already present. WSSV can spread horizontally through infected shrimp, contaminated water, equipment, vectors and cannibalism of infected animals. Broodstock can also be associated with transmission of WSSV to the next generation during spawning. However, according to the World Organisation for Animal Health, true transmission of WSSV from inside the egg itself has not been conclusively demonstrated. This is important for farmers purchasing post-larvae. A PL sample may test negative while a very low level of infection is present somewhere within the population. PCR remains an important screening tool, but the result represents the animals that were sampled. When viral prevalence or viral copy number is extremely low, infected individuals may not be included in a pooled sample or the amount of viral DNA may be near the detection limit. In other words, negative screening reduces risk, but it does not mean the farm can stop thinking about WSSV after stocking.

Why does WSSV suddenly become a problem during weather changes?

WSSV infection does not always immediately result in white spots or mass mortality. Shrimp can carry infection without obvious clinical disease. The situation can change when the environment changes. In Andhra Pradesh, farmers commonly experience periods of strong heat followed by rainfall, cloudy weather or sudden changes in pond conditions. Heavy rain can rapidly affect water temperature, salinity and other water-quality parameters, while cloudy weather and high organic loads may also increase the risk of low dissolved oxygen. WOAH specifically recognises environmental stress as an important factor in WSSV disease expression. Rapid changes in salinity can induce outbreaks, and water temperature strongly influences how WSSV infection develops. Therefore, the rain itself should not simply be described as "causing WSSV." A better way to understand the problem is:

WSSV may already be present → environmental conditions suddenly change → shrimp become stressed → host defence is compromised → viral replication and disease expression can increase → mortality follows.

This helps explain why farmers sometimes say,

The shrimp were eating normally yesterday, then suddenly after the weather changed everything started going wrong."

Once mortality starts, farmers have very few choices

There is currently no simple curative treatment that can be applied to a commercial pond and eliminate WSSV from infected shrimp. WSSV depends on living host cells for replication. However, this does not mean the virus immediately disappears when an infected shrimp dies. Dead and moribund shrimp can actually become important sources of infection for other shrimp through cannibalism and waterborne transmission. Once rapid mortality begins, therefore, the farmer's practical decision may be to harvest before the crop is completely lost, provided harvesting and disposal are managed with appropriate biosecurity. The problem is that the shrimp may still be 140, 150 or 160 count because they are stocked in the month of July or August only. Months of feed, electricity, seed, labour and pond-management costs have already been invested, but the crop has not yet reached the size where the farmer can obtain the expected return.

This is where a disease problem becomes a market problem.

So prevention must start before the weather changes

We cannot control the monsoon. But we can predict approximately when seasonal transitions are coming. This means management should shift from "What do we do after WSSV starts?" to "How do we prepare the shrimp before the high-risk period arrives?"

Shrimp Pathogen Testing in the LaboratoryPhoto credit: Blue Aqua Farmers Center (BAFC), India

Biosecurity, good-quality PL, molecular screening, stable water quality, adequate dissolved oxygen and control of environmental stress remain the foundation of WSSV risk management. Another important part is nutritional support for the shrimp's innate immune system before environmental stress occurs. Medium-chain fatty acids, or MCFAs, and their derivatives have received increasing research attention in shrimp nutrition. Zhou et al. (2023) studied dietary medium-chain fatty-acid products in Litopenaeus vannamei and reported improvements in several markers associated with non-specific immunity, including increased expression of prophenoloxidase and antimicrobial peptides. The supplemented shrimp also showed improved gut and hepatopancreas condition and greater resistance in a bacterial challenge model. Similarly, Shin et al. reported that a dietary mixture containing short- and medium-chain fatty-acid glycerides significantly enhanced innate immunity and antioxidant capacity in Pacific white shrimp. Perhaps particularly relevant to seasonal pond stress, Rairat et al. (2024) evaluated monoglycerides of short- and medium-chain fatty acids under low dissolved oxygen conditions. Shrimp receiving the higher supplementation levels showed significantly higher total hemocyte counts, phagocytic activity, phenoloxidase activity and superoxide dismutase activity. They also achieved higher survival under hypoxic stress than the control shrimp. These studies do not mean that MCT or MCFA supplementation cures WSSV. Instead, they support a more practical concept: prepare the shrimp's defence system before the period of environmental stress arrives.

Farmer mixes feed additive with shrimp feed before feeding.

Give the shrimp more time

The objective of preventive nutrition is simple. If disease pressure appears, stronger and less-stressed shrimp may be better positioned to cope with environmental challenges. The aim is to maintain feeding, health and resilience for as long as possible rather than waiting until severe mortality leaves emergency harvest as the only option.

AlphaGuard*L Plus provides an MCT-based together with herbal extracts designed to support shrimp health during periods of elevated stress. As part of a preventive feeding programme, AlphaGuard*L Plus can be applied at 3–5 ml/kg feed, for one meal per day, particularly before leading up to expected seasonal changes. It should not be considered a treatment or cure for WSSV. It should be considered one component of a broader preventive programme together with PL screening, biosecurity, oxygen management and stable pond conditions.

The goal is to give the crop a better opportunity to remain healthy, continue growing and reach a size that the market actually wants.

References

Andhra Jyothy. 23 August 2026. Local report on viral disease, oxygen problems and emergency shrimp harvests in the Mudinepalli aquaculture area.
The New Indian Express. 3 August 2026. El Niño takes a toll on aquaculture in AP.
World Organisation for Animal Health. Infection with White Spot Syndrome Virus. Aquatic Manual.
Zhou, W. et al. (2023). The effect of dietary supplementation of medium-chain fatty acids products on gut and hepatopancreas health, and disease resistance in white shrimp (Litopenaeus vannamei). Aquaculture Reports, 29, 101481.