56 SEPTEMBER 2024 • WORLD AQUACULTURE • WWW.WAS.ORG Shrimp health is largely impacted by water quality and the diversity of the microbial populations in the rearing water. Microbes that colonize the shrimp come from the rearing water and sediment. Evidence suggests that environmental factors affect these microbial communities include nitrates, nitrites, ammonia, salinity, pH, dissolved O2, and CO2 (Xiong 2016). The shrimp microbiota impact development and growth, the immune system, nutrition and metabolic processes, and the inhibition of pathogenic bacteria. Since 2009, White Feces Syndrome (WFS) has caused significant production losses for the shrimp industry in Southeast Asia. White Feces Syndrome is prevalent between 40-50 days of shrimp culture, affecting adult shrimp. Clinical signs of WFS are loss of appetite, a white or empty mid-gut, reduced growth, floating fecal strings, a loose exoskeleton, and chronic mortality (Figure 1). Initially, Enterocytozoon hepatopenaei (EHP) was identified as the causative agent of WFS because of its prevalence in affected ponds. Enterocytozoon hepatopenaei is an intracellular microsporidian that replicates in the tubules of the hepatopancreas causing symptoms similar to WFS without the fecal strings. Further investigations determined that the coinfection of shrimp with EHP and a strain of V. parahaemolyticus (toxR+, APHND-) elicited the white fecal strings associated with WFS but infection with each species separately did not. Recently the term pathobiome has been used to describe the idea that microbial communities interact with the host, with the potential result being either beneficial or harmful. In shrimp, EHP infection changes the biochemical balance, affects the immune response, and alters the integrity of the hepatopancreas allowing opportunistic pathogens to colonize and cause disease (Piamsomboon 2022). The prevalence of WFS at 40-50 days of culture is not surprising. As the animals age the pond water deteriorates through a process of eutrophication. Uneaten food and organic waste increase the organic matter content of the rearing water. This leads to increases in microbes involved in the degradation of organic matter and nitrification, decreases the pH and alkalinity of the water, and increases CO2. A study from Indonesia reported that WFS ponds showed lower pH (7.717.84) and dissolved oxygen (< 6mg ml-1) levels when compared to healthy ponds (pH > 8 and dissolved oxygen > 6 mg ml-1) (Piamsomboon 2022). Water quality and the microbiomes of both the rearing water and the shrimp are important to successful and sustainable aquaculture. Eubiosis describes a condition in which the host maintains a balanced microbiome resisting any disruption from internal or external factors. For example, the gut flora of healthy shrimp can be dominated by chitin-digesting Vibrio spp. living in harmony in the gut of the host without causing disease. Since there “What’s in the Water?” The Study of Shrimp Pond Microbiomes and Their Relationship to White Feces Syndrome Outbreaks Susan E. Knudson, Luke S. Keeton and ChaithanyaKrishna Reddy Noti FIGURE 1. Picture of a shrimp infected with WFS depicting the characteristic white gut. Photo taken by ChaithanyaKrishna Reddy Noti Since 2009, White Feces Syndrome (WFS) has caused significant production losses for the shrimp industry in Southeast Asia. White Feces Syndrome is prevalent between 40-50 days of shrimp culture, affecting adult shrimp. Clinical signs of WFS are loss of appetite, a white or empty mid-gut, reduced growth, floating fecal strings, a loose exoskeleton, and chronic mortality.
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