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Causes and Preventive Methods for White Feces Syndrome in L. Vannamei

CAUSES AND PREVENTIVE METHODS FOR WHITE FECES SYNDROME IN L. VANNAMEI

 

White Feces Syndrome (WFS)

 

The syndrome is named after the white faecal strings being excreted by affected shrimp. These white feces are seen floating at the surface of pond. Several problems are associated with the WFS, including reduced feeding, reduced shrimp growth, size disparities and chronic mortalities.
 

Symptoms at the Pond Level

 
  • More common when the weather changes drastically or the water temperature fluctuates.
  • Sudden increase or decrease in ingestion in the early stage; decrease or cessation of ingestion in the late stage.
  • Atrophy of the hepatopancreas, empty gut and empty stomach.
  • Separation of shell and flesh.
 

Source of images: Luis Fernando Aranguren et al., 2019

(a)
Floating, white fecal strings.
(b)
White fecal strings on a feeding tray.
(c)
White intestine of affected shrimp.
(d)
Affected shrimp’s golden-brown intestine with liquid contents.
(e)
Photomicrograph of fecal string contents.

Source: Siriporn Sriurairatana et al ., 2014

 

Internal signs

 

There is an increasing prevalence of vermiform, gregarine-like bodies within the shrimp hepatopancreas (HP) and midgut. Light microscopy of squash mounts and stained smears from fresh HP tissue revealed that the vermiform bodies are almost transparent with no cellular structure. Transmission electron microscopy revealed that the outer non-laminar membrane of the vermiform bodies bears no resemblance to a plasma membrane or to the outer layer of any known gregarine, other protozoan or metazoan. Sub-cellular organelles such as mitochondria, nuclei, endoplasmic reticulum and ribosomes are absent.

 

Sometimes, when engulfed by the aggregated transformed microvilli (ATM), they can be misinterpreted as cyst-like structures by light microscopy, contributing to gregarine-like appearance. The cause of ATM is currently unknown, but formation by loss of microvilli and subsequent cell lysis indicate that their formation is a pathological process. If sufficiently severe, they may retard shrimp’s growth and may predispose shrimp to opportunistic pathogens. Thus, the cause of ATM and their relationship (if any) to AHPND should be determined (Sriurairatana et al., 2014).

 

WFS-causing factors

 
 

The causes of white feces may include poor quality of feed (presence of anti-nutritional factors or mycotoxins), bacteria (a number of species of Vibrio), algal toxin (cyanobacteria), gregarines, and EHP. All of thse factors have been show to damages the hepatopandreas. When the hepatopancreas, the largest internal organ in shrimps, is compromised and damaged, we observe "white feces."
The hepatopancreas supports digestion, immune regulation and other functions, which are related to most shrimp diseases.

 

Prevention and Control Methods of WFS

 
 

Feeding Management

 
  • Pay attention to abnormal increase or decrease in feed uptake and verify the condition of shrimp through microscopic examination.
  • Be cautious in feeding; increase or decrease according to the situation.
 

Choice of Feed

 
  • Use Grobest functional feed.
  • Before expected environmental stress, preventive feeding is carried out to reduce the chance of white feces.
 

Environment and Water Management

 
  • Improve waste discharge capacity to avoid water quality deterioration.
  • Add probiotics to the water to prevent proliferation of pathogenic bacteria and to improve waste degradation.
  • Refrain from overusing medications, as they may lead to hepatopancreatic damage.
 

Choice of PL

 
  • Use disease-free post-larvae.
 

Disease Management

  • When white feces are first discovered and the shrimp still ingest, use Grobest functional feed immediately till the white feces disappear.
  • Remove dead shrimp, leftover feed, fecal matter and other waste daily to avoid cross infection.
  • Use high-quality pathogen-free post-larvae.
 

Feeding Management

 

Use Grobest Functional Feed to:

 
  • Strengthen the intestinal immunity, protect the intestinal tract, increase palatability and resistance to diseases.
  • Stimulate non-specific immune functions in shrimp, help to enhance non-specific immunity, reduce the chance of viral disease infection, and introduce visible preventive effects against shrimp diseases.
  • Supplement vitamins and amino acids in abundance to provide physiologically required nutrients, satisfy the demand for enzymes and trace elements, promote metabolism, and help maintain the healthy growth and development of shrimp.
  • Supplement selected glucans to improve the structure of intestinal flora, promote metabolism, protect cells from free radicals, maintain normal cell metabolism, and enhance resistance.
  • Promote the production of digestive enzymes, improve digestion, improve growth efficiency with anti-oxidant functions.
  • Increase disease resistance and resilience of cells in animals to prevent diseases caused by stress.
 

Feeding Protocols 

 

Water Quality Index

 

Ammonia<0.3 ppm, Nitrite<1 ppm, D.O.4 ppm, pH 7.5–8.5. When abnormal, use Grobest water treatment solutions—PSB and EM bacteria—to regulate the water quality, along with functional feed.

 

Recommended Application

 
  • PL stage (DOC<30): use for 15 consecutive days for prevention.
  • Regular prevention: use for 5~7 consecutive days every two weeks.
  • Disease peak season: use for 7 consecutive days before the environmental changes or disease season.
  • When white feces are discovered: use immediately for 3 consecutive days to diminish the symptoms.