Health and Disease Management
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Removing the sludge from the pond bottom daily via the shrimp toilets and improving aeration during the growth cycle are important. The sludge removed from ponds go into the discharge canal and later into the riverine environment. This is purely moving sludge from one place to another and not true disposal. In fact, AHPND could be easily spread to other farms via this movement and constitutes a biosecurity hazard. In my experience, I have seen attention to cleaning of ponds diligently but less on cleaning of discharge canals. While the industry searches for an effective solution, prevention is the only option today. For new farms that have not experienced AHPND, count yourselves lucky but do not be complacent or be overtaken by greed because once an outbreak occurs, it will take a long time before it can be overcome. Tan says that often there is full attention to cleaning of ponds but less on cleaning of discharge canals.
Via vertical transmission, these Vibrio spp are transferred to the post larvae.
Food for thought In my farming experience, I have never seen P. monodon affected by AHPND although I have heard non-verified observations of this happening. Is this due to the lower stocking density when farming the monodon shrimp and thus lower sludge content in the pond bottom?
What to do to prevent EMS/AHPND? There really is no one single method but a holistic approach is required. The first is to reduce the stocking density to 60-80 PL/m2. This reduces the stress environment of overcrowding, high feed input (consequential uneaten feed) and faeces output. I want to highlight that many post larvae suppliers provide 10-20% extra animals and sometimes more to placate the farmer when quality is sub-standard, but these have not been counted in the stocking density. We should absolutely avoid the use of live polychaetes and live animals as broodstock feeds. The downside here could be lower fecundity rates from the broodstock. Hatcheries/farms should perform all quality control checks for AHPND before the post larvae are stocked into ponds. Nurseries under controlled environment and high oxygenation (as extension of hatcheries) have been able to improve early stage care with better nutrition to produce stronger animals before being stocked into ponds.
Based in Thailand, Robins McIntosh is executive vice president for technical development of shrimp culture within the Charoen Pokphand Group (CPF). He joined the Group in 2001 to assist with the restructuring of shrimp culture in Thailand increasing the efficiency of shrimp culture and finding solutions to eradicate EMS/AHPND and EHP diseases in shrimp. Prior to the onset of EMS, Thailand averaged over 85% survival in ponds and a pond failure rate of less than 5%. Today pond survival rates average less than 75% with a failure rate exceeding 5%. The first four years of the EMS (2009-2013) was defined by massive mortality
March/April 2019 AQUA Culture Asia Pacific