About White Feces Disease
White Feces Disease (WFD) has become a growing problem for shrimp production. Many factors are related to its increase over the past few years, including:
- deteriorating water quality due to increased organic load from upstream industry
- the impact of higher stocking densities
- excessive feed use leading to higher levels of sediment waste.
Additionally, environmental factors can promote disease inducing conditions, such as increases in seasonal temperatures, heavy rain that reduces pond salinity or impacts pH, and poor water quality from rivers with higher salinity due to rising sea water.
What Causes White Feces Disease?
The exact causative agent has not been identified. Research on WFD shows that it could be due to an infestation of various Vibrio bacteria. A number of Vibrio species have been identified with WFD. For example, Vibrio parahaemolyticus, V. fluvialis, V. mimicus, V. alginolyticus, as well as other Vibrio spp. have been isolated from the feces of WFD-infected shrimp. Additionally, EHP (Enterocytozoon hepatopenaei), a microsporidian parasite, has also been associated with WFD, but causation has not been confirmed. Lastly, the disease may also be caused by physical sloughing of hepatopancreatic tubules, possibly due to a new, unidentified, bacterial toxin.
Many potential factors are thought to contribute to WFD:
- High stocking densities
- Poor pond bottom conditions, including those with a lot of sludge
- High algae bloom due to poor water management
- Pond water with low transparency of <20 cm
- Significant algae crash coupled with rising total ammonia nitrogen (TAN)
- Cyanophyta being replaced by dinoflagellata and ciliata/protozoa in the pond
- Poor feeding management strategies that can result in a lot of uneaten feed left in pond
- High total Vibrio count in water, defines as a count of > 1 x 104 CFU/mL, or >12% of the total bacteria load
- High alkalinity, defined as >200 ppm or <80 ppm
- Prolonged low dissolved oxygen, defined as <3.0 ppm
- Poor pH management
For more information about WFD, such as how to identify WFD and tips for preventing WFD, see our technical bulletin.