Enterocytozoon hepatopenaei (EHP), a fungal microsporidian parasite that commonly infects the hepatopancreas of white-leg shrimp (Penaeus Vannamei), is now arguably the key health concern for many producers across Asia. The ingestion of spores results in the infection of epithelial cells lining the tubules of the hepatopancreas. The subsequent proliferation and release of spores either by exocytosis or consequential cell breakdown, impacts the digestive capacity of shrimp, resulting in slow growth and a notable variation in the stock size. Chronic infections can lead to the loss of stock.
Controlling EHP in farm environments is a challenge. The key to its management lies in strict biosecurity and disease surveillance practices, i.e., in the rigorous disease testing of stock, feeds and water at each point in the production chain; avoiding the introduction of infected batches of post-larvae and water into ponds; avoiding the overstocking of culture systems; ensuring effective water and waste management; ensuring the comprehensive disinfection of ponds between crop cycles; as the original source of EHP has as yet to be determined, it is important that all alien organisms are excluded, and their entry into culture systems are prevented; likewise the on-farm movement of equipment between ponds should be avoided where possible unless robust disinfection procedures are in place; and, that the number of shrimp, the sampling strategy and the diagnostic methods used, are appropriate for the sensitive and confident early detection of infections.
For the past 30 months, the disease management component of the Shrimp Health Resources Improvement project (SHRImp), a project funded by the Walmart Foundation and IDH (the Sustainable Trade Initiative), and conducted by a collaborative team of scientists from Fish Vet Group Asia, who have now amalgamated with INVE Thailand (Benchmark Group), and FAI have been running mobile shrimp health clinics in three Thai provinces to support farmers in their shrimp health testing needs.
The clinics operating out of the shrimp clubs offer health evaluations and molecular disease testing for AHPND (EMS), EHP and WSSV. Farmers can drop off samples, which are processed while they conduct club business. The results are relayed back to the farmer by phone and through a purpose-designed software platform that runs on a mobile phone – app.MyShrimp.farm. Access to the application has several layers of security so that the confidential results can only be seen by the farmer, who can decide who they wish to share their results with.
In 2019, 129 farms, 451 ponds and >13,250 shrimp were tested; infection rates across the three provinces ranged from 44.1%-95.2% (av. 48.6%). Infection rates in earth or slope-only lined ponds were higher (65.9%) than fully lined ponds (46.3%). Looking at other combinatorial factors such as the presence of shrimp toilet or not, found that infection rates in earth and slope only ponds with no toilet were higher (81.1%) when compared to fully lined ponds with a toilet (60.9%). Project findings saw a rise in infection rates to 84.8% by the end of the second half of 2019, while the testing of a further 262 ponds throughout 2020 suggested an infection rate of 93.5%.
|INVE Aquaculture authors|
|Other authors: Pau Badia, Nitrada Yamuen, Chatbongkot Meakniti, Kultida Khwankuea, Audrey Burkard, Marius Nicolini, Tarinee Limakom, Anton Immink, Olivier Decamp and Ralf Onken|
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