PCR: An Accurate Way to Detect Diseases in Vannamei Shrimp

Vannamei shrimp diseases continue to be a major cause of mass losses in shrimp farms. One of the most crucial steps to prevent such losses is through early and accurate disease detection.

The results of disease detection serve as key references for deciding preventive actions in shrimp ponds. Measures such as administering probiotics or feed additives depend heavily on these results.

To ensure accurate disease detection, it is essential to have advanced systems and technologies in place. Therefore, investing in disease detection processes is vital to maintaining productivity in shrimp farming.

One of the pathogens most concerning to vannamei shrimp farmers is Vibrio, a bacteria responsible for several chronic diseases in shrimp that can lead to significant losses.

For example, Vibrio parahaemolyticus, which causes Acute Hepatopancreatic Disease (AHPND) in shrimp, has resulted in 11.58 billion USD in losses and over 100,000 job losses in Thailand, according to data from The Fish Site.

With early and precise detection of vannamei shrimp diseases, potential losses can be minimized, ensuring the sustainability of shrimp farming operations.

Common methods for detecting diseases in vannamei shrimp include chromogenic agar and Real-Time or Quantitative Polymerase Chain Reaction (qPCR).
 

Detecting Diseases in Vannamei Shrimp Using Chromogenic Agar

Chromogenic agar is a substrate used for bacterial cultures. However, it only displays specific colors that correspond to certain bacterial colonies.

Chromogenic agar contains chromogenic substances that release specific colors when stimulated by certain enzyme activities. These enzymes are natural substances secreted by pathogenic bacteria. Thus, chromogenic agar can detect pathogenic bacteria based on the enzymes they excrete.

In short, the colors that appear on chromogenic agar allow shrimp farmers to visually detect the pathogens causing vannamei shrimp diseases. The use of chromogenic agar is common for detecting Vibrio in vannamei shrimp.

Here is an example of using chromogenic agar to detect Vibrio bacteria. 

The purple color on the chromogenic agar results from the specific enzyme activity of Vibrio parahaemolyticus. Thus, it can be concluded that the sample contains Vibrio bacteria.
 

Disease Detection in Vannamei Shrimp with PCR

The term PCR may be familiar from the recent pandemic as a method to detect COVID-19 infection. However, this method is also widely used in various fields, including aquaculture.
 

PCR is a method used to identify specific genetic material in a sample. Therefore, this method can be utilized to identify pathogen species at a molecular level.

One PCR method frequently used in shrimp ponds is real-time PCR or qPCR. This method not only identifies pathogen species but also quantifies the pathogen, indicating its spread in shrimp.

qPCR has advantages over conventional PCR, as the data can be viewed in real-time graphs, unlike conventional PCR results that require electrophoresis.

Here is an example of the detection results for Vibrio in vannamei shrimp using the qPCR and conventional PCR methods.

 

The image on the left shows the results of Vibrio detection in vannamei shrimp using qPCR, represented by a graph that can be directly analyzed to determine the presence and quantity of Vibrio bacteria.

The image on the right displays the results of the electrophoresis process of Vibrio genetic material, matched with the sample to confirm the presence of Vibrio bacteria.
 

Comparison of qPCR and Chromogenic Agar

The qPCR method has several advantages over chromogenic agar in disease detection, particularly in accuracy and detection time.
 

Accuracy Level
Based on molecular-level analysis, the qPCR method provides more accurate results than chromogenic agar, which relies on enzymatic activity.

Chromogenic agar can still be used as a simple analysis to give an early indication of vannamei shrimp diseases in a certain area. However, the results from chromogenic agar need further confirmation and cannot be used as the sole basis for actions to be taken.

With the qPCR method, farmers can accurately identify the pathogen species and estimate the pathogen's abundance at the time of sampling.

Additionally, there are several potential biases in species determination when using chromogenic agar due to the following factors:

• Temperature effects

• Similarity in color between species

The color results on chromogenic agar are susceptible to changes caused by temperature fluctuations, making species identification less accurate.

For example, in detecting Vibrio in vannamei shrimp, the color outcome may shift from indicating Vibrio parahaemolyticus (light purple) to Vibrio harveyi (dark purple).

There is also potential species bias when interpreting the light purple color that appears. This color could be caused by Vibrio parahaemolyticus (causing AHPND), Vibrio parahaemolyticus non-AHPND, or Vibrio hepatarius.

This could lead to inaccurate detection of Vibrio in vannamei shrimp and ineffective prevention of AHPND.
 

Disease Detection Duration

The process of detecting vannamei shrimp diseases using qPCR is relatively faster compared to chromogenic agar.

qPCR detection takes only a few hours, much shorter than the chromogenic agar method, which can take more than a day. This is because chromogenic agar requires an incubation period for the bacteria to grow first.

Chromogenic agar shows color results after the target bacteria have grown and formed colonies. In contrast, qPCR only requires the extraction of genetic material and analysis using the qPCR machine.

For example, detecting Vibrio in vannamei shrimp using chromogenic agar can take around 18-24 hours for the incubation period.
 

Check Your Pond's Health with CeKolam

CeKolam offers disease detection services, including Vibrio detection in vannamei shrimp, using accurate and fast Real-Time PCR technology.

CeKolam is a disease detection service led by Nusantara Genetics, also known as Nusantics. Nusantics has gained a reliable reputation for providing PCR testing services during the pandemic, with over 8 million of their products used to detect the COVID-19 virus.

With CeKolam's Real-Time PCR technology, vannamei shrimp diseases can be detected even before the first symptoms appear. This advantage allows farmers to take preventive action before massive losses occur.

Partner with CeKolam from Nusantics for early disease detection and avoid losses of up to billions of rupiah. Check out the service here: 0882-1877-4777

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Reference: 

https://thefishsite.com/articles/yang-perlu-anda-ketahui-tentang-ems-ahpnd-dalam-budiday a-udang 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5355637/ 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC93376/ 

http://ejournal-balitbang.kkp.go.id/index.php/jra/article/view/8145/6741 https://www.labunlimited.co.uk/pdf/2054_en_2.pdf

https://www.labunlimited.co.uk/pdf/2054_en_2.pdf