USA: Two months after launching a case study on early mortality síndrome (EMS), Global Aquaculture Alliance (GAA) President George Chamberlain says EMS continues to take a toll on the global shrimp-farming sector, but advancing knowledge is progressively leading toward improved practices and better control of the disease.
In a recent presentation to members of the National Fisheries Institute Shrimp Council, Chamberlain updated the EMS status of primary production areas and passed on recommendations for management methods to reduce the impacts of EMS.
Chamberlain said the incidence of EMS in China varies among regions. In early 2014, EMS appeared at a low rate in eastern and southwestern Guangdong, and Guangxi provinces, but manifested at moderate to high rates in the Pearl River and Zhangjiang regions. Farms in northern China had not been stocked.
He also noted that despite the presence of EMS, recent high shrimp prices continued to fuel rapid farm expansion in Vietnam. Now that prices have dropped to USD 5.00/kg, fewer farms are stocking, and postlarvae sales are dropping.
Thailand was again hit hard by EMS. First quarter estimates showed only 30,000 tonnes of production versus 100,000 tonnes last year. Coming off three months of low temperatures and facing continued failure rates of over 30 per cent in the first 40 days, many farms are not expected to restock for a time.
In Malaysia, production remained down overall, although concerted efforts at the large-scale farm run by Agrobest are yielding rising results.
Chamberlain said Mexico’s first outbreaks of EMS came at Nayarit in the center of Sinaloa and a couple of farms in Sonora. New farms starting in the south and on the Gulf of Mexico seem to have escaped EMS so far. Head-on shrimp production of 55,000 to 60,000 tonnes is projected for the country.
India faces an unsure prognosis regarding EMS. Test results have been inconsistent and inconclusive, so the country’s producers should be considered free of EMS at the present time.
Chamberlain shared a number of observations and recommendations made by members of an expert committee on EMS formed by GAA. For example, those working with EMS have identified varying toxicity in the multiple strains of the Vibriobacteria that cause the disease. Although test methods are improving, EMS losses continue to be confused with mortalities caused by viral diseases such as the white spot syndrome and Taura syndrome.
EMS is thought to be transmitted vertically (on the outside of eggs) from broodstock to postlarvae, and can also transfer to shrimp via water, cannibalism, feces, plankton, macro-organisms, birds and biofilms. Once established in the environment, EMS is difficult to control, Chamberlain said.
Importantly, it has been found in China that antibiotics are not effective against EMS. Sensitivity tests have shown the bacteria responsible for EMS outbreaks have already developed resistance to the full range of antibiotics. Research in Mexico shows that pathogenic Vibrio strains have nearly the same resistance profiles as non pathogenic strains. However, Mexican researchers agree that antibiotics are not effective, because they do not effectively reach the pathogen which colonizes chitinous surfaces.
GAA is launching a new online survey to collect additional information on the EMS status of farms in affected areas, as well as the practices they apply to combat the disease.
The comprehensive survey -- funded by the World Bank Allfish project, the Seafood Industry Research Fund of the National Fisheries Institute and C.P. Prima of Indonesia -- will initially be available in English at the GAA website. Versions in other languages will be added to better allow those in Asian and Latin American countries to participate.
Based on responses to the survey, a select number of farms will be chosen to receive in-depth site audits and diagnostic testing to clarify what practices are most effective in managing EMS. In combination with the survey results, these findings will be distributed by GAA to help identify the common denominators of proper management and promote the adoption of better shrimp-farming practices industry wide.