In recent years, Enterocytozoon hepatopenaei (EHP) has become one of the major threats to the aquaculture industry, particularly in the farming of white shrimp (Litopenaeus vannamei) in Southeast Asia. EHP is a microsporidian parasite that primarily infects the hepatopancreas of shrimp, causing atrophy of hepatopancreatic tubules, which in turn negatively impacts shrimp growth and survival rates. Despite advancements in aquaculture technology that have improved shrimp larval survival rates, the prevalence of EHP infections continues to rise. This increase is closely tied to complex environmental factors.

EHP infected shrimp show greater size variation.

Key Environmental Factors Driving the Rise in EHP Infection Rates

1. The Widespread Adoption of High-Density Farming

In intensive farming environments, EHP spores can easily spread through feces, contaminated feed, or water, leading to widespread infections.

2. Poor Water Quality Management

Overfeeding often results in eutrophication of water, increasing concentrations of harmful substances like ammonia and nitrites. This weakens shrimp immunity, making them more susceptible to EHP infections.

3. Environmental Pollution and Land Use Changes

The rise in agricultural chemicals and industrial wastewater pollution places farmed shrimp in chronic stressful environments, weakening their resistance to diseases and indirectly increasing threats like EHP.

4. The Impact of Climate Change

Climate change has led to extreme weather events such as high temperatures, heavy rainfall, and droughts, which significantly affect farming environments. For example:

• High temperatures accelerate the proliferation of harmful pathogens, including EHP, in water bodies.
• Heavy rainfall not only stresses shrimp but may also enable pathogens to spread further through flooding.

5. The High Resilience of EHP Spores

The environmental resilience of EHP spores is another critical factor behind the increasing infection rates. EHP spores can survive in the environment for weeks to months and may persist even after standard disinfection processes. This enables infections to recur between production cycles, leading to repeated outbreaks.

How to Address the Environmental Challenges of EHP Infection

1. Improving Water Quality Management

Effective water quality management is fundamental to reducing disease infections. Regular monitoring of ammonia, nitrite, and dissolved oxygen levels in the water is essential. Measures such as controlling feed quantities, using probiotics, and applying soil conditioners can significantly enhance the water environment. Additionally, a well-designed drainage system to prevent the accumulation of organic matter is an effective way to reduce EHP infections.

2. Enhancing Shrimp Larvae Quarantine Procedures

Before introducing shrimp larvae to the farm, suppliers should be required to provide EHP testing reports. Farms should also conduct rapid EHP tests on shrimp larvae themselves to avoid introducing infected stock into the water system.

3. Reducing Stocking Density

While low-density farming may yield lower production, it reduces stress on shrimp, resulting in higher immunity and survival rates. Additionally, low-density environments often achieve better feed conversion rates and lower pathogen concentrations in the water, helping to control EHP spread.

4. Strengthening Environmental Disinfection and Facility Maintenance

After each harvest cycle, farms should routinely use high-efficiency disinfectants to clean residual materials from pond bottoms. This minimizes the presence of EHP spores and reduces the risk of recurring infections.

5. Using High-Quality Feed Additives

Feed additives formulated with natural extracts (e.g., EHPurge) can effectively boost shrimp growth and immunity, reducing the likelihood of EHP infections. These additives also help shorten the farming period, lowering the risk of infections from various diseases.

Regular monitoring of ammonia, nitrite, and dissolved oxygen levels in the water is essential for shrimp farming.

Conclusion

The rise in EHP infection rates is the result of multiple environmental factors, including high-density farming, inadequate water quality management, climate change, and the resilience of pathogens itself. To effectively curb the spread of EHP, it is crucial to improve farm management practices and adopt effective environmental control measures.

Author: Barry Cheng, Manager of Aquaculture Department