EHP IS A THREAT TO SHRIMP FARMING

  • Monday, 23/09/2019, 16:25 GMT+7
  • Views: 801

EHP has been present in shrimp for many years. Until 2016, the disease officially broke out and in 2019, EHP became an important issue not only for Vietnam but also for the world.

EHP is an abbreviation for Enterocytozoon hepatopenaei, a microsporidean which is a spore forming parasite. They attack shrimp by destroying the shrimp's digestive system, also known as hepatopancreatic spore disease. EHP reduces production and adversely affects shrimp industry in many countries such as China, Vietnam, Thailand, Malaysia, Indonesia and India.

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Source: GAA

EHP spores are tubular, long, twisted. When activated, they transferred the gene into a shrimp hepatopancreas cell, where the spore doubled. The mechanism of activation of spores may be related to pond bottom pollution. The severity of the disease increases when the density of activated spores in the epithelium is high.

EHP is confined to the hepatopancreatic tubular cells of shrimp, it destroys the digestive and absorptive capability of cells. EHP damages the ability of hepatopancreatic cells and hence deprives the shrimps from nutrition resulting in poor growth and production. Histologically, larger eosinophilic to basophilic inclusions were observed in distal end tubular epithelium of hepatopancreas indicating the presumptive developmental stages of EHP. Basal membranes of hepatopancreas were detached from tubular epithelium with sloughing of the tubular epithelial cell in case of heavy infections followed by cellular damage.

How to detect / Diagnose EHP?

  • Histological method
  • Molecular biology method
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How to detect EHP in farming systems

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There are significant differences in shrimp sizes

 

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The shrimp gut gradually disappears and the hepatopancreas turns green, which is associated with white feces

 

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Shrimp grow slowly, the gut gradually disappears, turning grayish green

 

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The gut curled, the position adjacent to the stomach and the hepatopancreas was white

How to control EHP in hatcheries

  • It is strictly advisable that the live feed such as polychaete worms, clams, oysters, Artemia and other inputs need to be screened for pathogens before their use in the hatcheries. It has been suggested that freezing polychaete worms could help in reducing infectivity of microsporidia.
  • Another preventive measure could be pasteurization of live feed before feeding. This will also destroy most bacterial and viral pathogens.
  • Washing eggs and nauplii with iodine, formalin,... will help in reducing number of microsporidial spores if any.
  • Disinfection of hatchery facility prior to starting new production cycle will help in minimizing EHP risk. Cleaning hatchery facility including all the surfaces, tanks, pipelines and implements, with 2.5 % sodium hydroxide solution with a minimum of 3 hours of contact time and then drying for about a week followed by rinsing with acidified chlorine (200 ppm) is advocated to prevent EHP.

How to control EHP in farms

Causes of EHP:

  • PL is infected.
  • Pond bottoms of previous crops infected with EHP were not thoroughly treated.
  • Waste content is high.

Once the infection occurs, there is no known treatment. The spore is nearly indestructible. The infection starts with broodstock. If the broodstock comes in contact with the spore, all the nauplii it produces will carry a spore that will then infect the post larvae and then the farm. If many farms in an area become infected, the waterways will carry the spores as well, and bring them into uninfected farms, or hatcheries or broodstock grow out ponds using the same water. Therefore, comprehensive measures are needed to control.

Water must be disinfected before it is pumped to farming ponds.

Need to check the density of vibrio in water and in pond soil before managing water color.

Choose to buy shrimp post-larvae from reputable and good-quality suppliers. Depending on the scale and farming techniques, adjust stocking density at a moderate level.

During the farming process, monitor pond indicators such as pH, temperature, alkalinity, and dissolved oxygen. Timely adjust indicators to appropriate levels. Avoid shrimp shock caused by environmental factors, which will create conditions for pathogens to develop.

Track, care, and manage shrimp’s feed intake. Avoid leftovers. Regularly check shrimp color, hepatopancreas and size.

Use complementary foods to increase health and resistance.

Traslate: Tran Thi Thuy Quyen

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