White Feces Syndrome (WFS) is a gastrointestinal disorder in cultured penaeid shrimp, causing severe economic losses and production issues worldwide.
Researchers from Chulalongkorn University and Kyungpook National University published a review summarizing the information on the association between White Feces Syndrome and water parameters, intestinal microbiomes, Enterocytozoon hepatopenaei (EHP), Vibrio, and disease control strategies.
Characteristics of White Feces Syndrome
White Feces Syndrome is characterized by the presence of white feces floating on the surface of shrimp ponds. Infected shrimp typically exhibit whitish to yellowish midguts, stunted growth, high size variation, reduced average daily growth, elevated feed conversion rates, loose exoskeletons, and sometimes mortality.
Shrimp with WFS generally show reduced feed intake and growth rate, hepatopancreatic discoloration, and loose shells.
The syndrome typically occurs around 50 to 60 days after stocking.
Water Quality Parameters and WFS
Few reports link water quality to the occurrence of WFS. The syndrome has been reported in environments with both low (<5 ppm) and high (>30 ppm) salinity.
For example, mortality after WFS incidence in black tiger shrimp (Penaeus monodon) was observed at low dissolved oxygen levels (>3 mg/L) and low alkalinity (<80 ppm) in Thailand.
However, researchers conclude that water quality generally does not have a direct impact on WFS occurrence but may affect shrimp health and pond microbial populations indirectly.
Etiology of White Feces Syndrome
Bacterial Pathogens Associated with WFS
Bacterial infections causing whitish or yellowish gastrointestinal exudates have been reported in shrimp, not limited to White Feces Syndrome.
These gastrointestinal materials were caused by exudative inflammation and excessive mucin production induced by bacteria. Vibrio was a major focus during the initial investigation of WFS.
Vibrio spp. seem to play a significant role in the occurrence of WFS, as a significantly higher load of Vibrio spp. was found in the water, intestines, and hemolymph of shrimp affected by WFS compared to healthy individuals.
Microbiome Analysis of Shrimp with WFS
It has been suggested that dysbiosis of the intestinal microbiota or imbalance in the microbial community in the GI tract is strongly associated with WFS occurrence.
Studies found that the intestinal microbiome of shrimp with WFS has low α-diversity and is less homogeneous.
Opportunistic pathogens like Vibrio, Candidatus Bacilloplasma, Phascolarctobacterium, Photobacterium, and Aeromonas were overrepresented in shrimp affected by WFS, while beneficial bacteria like Shewanella, Chitinibacter, Rhodobacter, Paracoccus, and Lactococcus were more abundant in healthy shrimp.
Association between EHP and Vibriosis in WFS Occurrence
Scientific evidence supports the association between WFS and Enterocytozoon hepatopenaei (EHP). Shrimp farms with Litopenaeus vannamei exhibiting WFS showed EHP spores in their fecal threads, midgut, and rod-shaped bacteria.
All collected intestinal samples from shrimp affected by WFS in India and Vietnam tested positive for EHP, with spores detected inside and around the transformed microvilli. In contrast, approximately 90% of intestines from normal shrimp in affected farms tested EHP-positive.
WFS is associated with a synergistic effect between EHP infection and other pathogens. EHP may weaken shrimp by altering infected hepatopancreatic cells.
Treatment of White Feces Syndrome
To date, no novel treatment for WFS has been found. Preventive measures, such as strict biosecurity systems to eliminate or inactivate EHP spores and limit the total number of Vibrio, have been suggested.
A combination of physical, chemical, and biological controls is recommended for managing WFS.
Conclusion
White Feces Syndrome (WFS) is a gastrointestinal disorder in shrimp associated with Enterocytozoon hepatopenaei (EHP) and other bacteria like Vibrio and Propionigenium.
EHP induces disruption of hepatopancreatic tubules, and detached cells moving through the gastrointestinal tract aid the growth of opportunistic bacteria.
Despite causing significant economic losses in shrimp-producing countries, no ideal treatments or control methods for WFS have been found. Thus, strict biosecurity systems are suggested for eliminating EHP spores and managing Vibrio to prevent WFS.
The study was funded by the Basic Science Research Program through the National Research Foundation of Korea (NRF), financed by the Ministry of Science and ICT, and the Ministry of Education.
Reference (open access)
Piamsomboon, P.; Han, J.E. White Feces Syndrome, A Multifactorial Syndrome of Cultured Shrimp: A Mini Review. Fishes 2022, 7, 339. https://doi.org/10.3390/fishes7060339
