The collapse of an industry
In the early 1990s, Sri Lanka's shrimp farming industry, centered around the monoculture of the giant tiger prawn (Penaeus monodon), was expanding rapidly. By 1994, the country had around 250 authorized farms and the industry provided over 4,000 jobs. This period of growth came to an abrupt end in 1996 with the arrival of White Spot Syndrome Virus (WSSV). First identified in Taiwan in 1992, the virus had spread throughout East and South Asia by 1996.
WSSV is a highly contagious and lethal pathogen for crustaceans. It is a large, rod-shaped, double-stranded DNA virus belonging to the family Nimaviridae. The virus infects tissues of ectodermal and mesodermal origin, such as the gills and the connective tissues under the shell. Its replication is rapid, leading to mass mortality events where death rates can reach 100% within 3 to 10 days of the first clinical signs. The most common signs of infection are a sudden drop in feed consumption, lethargy, and the appearance of characteristic white spots, 0.5 to 2.0 mm in diameter, on the inside of the carapace. The 1996 outbreak in Sri Lanka, like in many other Asian countries, led to a near-total collapse of the shrimp farming sector, causing immense economic damage.
Lessons in biosecurity
The WSSV crisis forced a complete re-evaluation of shrimp farm management. The uncontrolled proliferation of farms with poor environmental oversight was recognized as a contributing factor to the disaster. In the aftermath, a new focus on biosecurity emerged as the primary defense against future outbreaks. Since there is no treatment for WSSV, prevention is the only effective strategy.
Modern biosecurity protocols, many developed from the hard lessons of the 1990s, are now standard in global aquaculture. A fundamental step is stocking ponds with specific-pathogen-free (SPF) post-larvae from screened hatcheries. All incoming water must be treated, often involving filtration to remove carriers like crabs or copepods, followed by disinfection with chlorine or UV sterilizers. Farms now implement strict access controls, including fencing ponds to exclude crabs and netting to keep out birds, both of which can act as vectors for the virus. Simple measures, like disinfecting boots and equipment between ponds, are also enforced to prevent cross-contamination. Holding water in reservoirs for at least 72 hours before use can help inactivate free-floating virus particles. These practices, born from economic catastrophe in places like Aluthgama, now are the foundation of sustainable shrimp aquaculture worldwide.