In Vietnam, Dr Dang Thi Hoang Oanh, Cantho University, Vietnam
noted that incidences were more severe in farms with high salinity
water and during the hot season (April to July), but water quality was not
the main cause. Her experiments on the route of transmission included
placing shrimp in hapas in EMS affected ponds. She concluded that
transmission occurred via water and co-habitation. Hoang said that in
2012, EMS was also reported in hatcheries. Improvement in production
in Vietnam will be through the use of specific pathogen free (SPF) post
larvae (PL), produced from a two-phase hatchery (30days) and nursery
(45 days) system, with grow-out in square ponds of 2,000 to 3,000 m2
equipped with 28 hp aerators and bottom diffusers.