When EHP in an area is left untreated, bad things happen. It has been especially prevalent in China for a number of years. The spores build up in the environment, resulting in slower and slower growth.
If the first year farmers could produce 20-gram shrimp, they might see 15-gram shrimp in year two, and 10-gram shrimp in year three.
This is largely the story of China shrimp culture at the moment. Farmers have been unable to produce large shrimp, and they are turning to antibiotic use to treat disease.
As a result, China exporters have had to import shrimp both to get the size range they needed, and to guarantee antibiotic-free shrimp to ship to the US and elsewhere.
The spike in rejections of shrimp from Malaysia due to high levels of antibiotic residue is also to be traced to this problem. Chinese growers who could not sell to local processors apparently transshipped their shrimp to Malaysia, and the rejections for antibiotics spiked by the FDA.
In recent months Malaysia has cracked down and successfully prevented this practice, and FDA rejections have fallen sharply as well.Finally, unlike EMS that led to widespread mortality, it appears that the impact of EHP is more akin to that of sea lice on salmon.. it slows their growth and weakens them but is not usually fatal.
As a result, it will be hard to pick the EHP signal out of the normal variation in shrimp farming results based on weather, other diseases, feed and broodstock health.
EHP is not likely to dramatically collapse production the way EMS did, however it is a headwind that will prevent production growth to a greater or lesser extent in various regions.
Because detection has not been perfected it is hard to know for sure the extent to which the spores already have spread.
It does seem clear that the newer production areas where there has been a spectacular growth of output, such as India, will see a leveling off as ponds become less productive in their third or fourth year, leading to lower density, or more failures to grow large shrimp in higher density ponds.
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