Early Mortality Syndrome (EMS), also known as Acute Hepatopancreatic Necrosis Syndrome (AHPNS), is a severe disease affecting shrimp farming in Vietnam, including both white leg shrimp and giant tiger shrimp, whether in intensive or semi-intensive systems.

The disease was first reported in China in 2009, followed by its emergence in Vietnam in 2010. It was then identified in Malaysia and Thailand in 2011, and in Mexico in 2013.

Signs of shrimp affected by AHPND include empty midgut, pale and atrophied hepatopancreas, and empty intestine

1. Causes

The disease is caused by the integration of Vibrio parahaemolyticus bacteria with a toxic phage, resulting in the production of a potent toxin that destroys tissues and disrupts the function of the hepatopancreas in the shrimp’s digestive system. This is the underlying cause of early mortality in shrimp within the first 30 days after stocking, with mortality rates reaching over 70%.

Vibrio parahaemolyticus bacteria

The disease is divided into two stages:

  • Initial stage: Vibrio parahaemolyticus infection with phage secretion of toxins weakens the shrimp and impairs their immune response.
  • Later stage: A second wave of bacterial attack occurs, releasing toxins that disrupt the function of the hepatopancreas and cause necrosis of the shrimp’s hepatopancreatic tissues, leading to mass mortality.

This mechanism explains why the disease is difficult to prevent, and why antibiotic treatment does not yield the desired effect.

2. Symptoms

In a shrimp population affected by the disease:

  • During the initial stage, the symptoms may not be clearly visible.
  • Shrimp exhibit slow growth and may die at the bottom of the pond.
  • Affected shrimp may have soft shells and undergo color changes.
  • Sick shrimp often display listlessness, clustering in certain areas, flipping over on the water surface, reduced appetite, and subsequent death.
  • Shrimp can die very quickly, within 2-3 days after the disease is detected.
  • Many cases have reported shrimp suspending mortality during fasting and then rapidly dying upon resumption of feeding.

On individual shrimp:

  • The affected shrimp’s hepatopancreas may exhibit various conditions, including swelling, softening, and discoloration, and in some cases, it may shrink and become firm. The shell can become soft and opaque.
  • Shrimp may experience prolonged white feces.
  • The color of the hepatopancreas appears pale.
  • The intestinal tract may be twisted or devoid of food particles.

Both shrimp have contracted EMS, as indicated by the atrophied hepatopancreas in both individuals

In the shrimp pond:

  • Decreased mineral content in the pond water.
  • Decreased water transparency to below 30 cm.
  • Dissolved oxygen levels below 5 ppm during the first month after stocking.
  • pH fluctuations of more than 0.3 within a day.
  • Toxic ammonia (NH3) appears early during the rearing period.

3. Preventive measures

Absolutely, disease prevention is crucial in minimizing the incidence of shrimp diseases. By implementing effective preventive measures, the likelihood of shrimp getting infected can be significantly reduced.

  • Doing well in pond renovation and maintaining good pond hygiene is crucial. Using environmental treatment products like VII FARM Aquaculture Environmental Treatment Probiotics to clean the pond and create a favorable environment for shrimp growth can be beneficial.
  • Choosing high-quality and certified shrimp breeds is important for disease prevention.
  • During the rearing process, it is essential to minimize shocks and avoid algal blooms that can affect the shrimp.
  • Supplementing shrimp feed with digestive enzymes (beneficial bacteria for the gut) like VII FARM Shrimp Digestive Enzyme can aid in digestion, provide additional gut bacteria, and compete against disease-causing bacteria.