A series of studies were conducted on an emerging disease in farmed penaeid shrimp. This disease was first named as Early Mortality Syndrome (EMS) or more descriptively as Acute Hepatopancreatic Necrosis Syndrome (AHPNS). As part of the outcome of this research, the etiology of EMS/AHPNS was demonstrated. EMS was first classified as an idiopathic disease because no causative agent had been identified. Preliminary studies conducted in Vietnam in 2012 by the University of Arizona Aquaculture Pathology Laboratory (UAZ-APL) indicated that EMS is infectious (Tran et al., 2013). The agent was identified as a unique strain of Vibrio parahaemolyticus. Hence, EMS has a bacterial etiology confirmed by satisfying Koch's Postulates. Further studies focusing on the bacterial isolate causing EMS revealed that the agent could produce toxin(s), which is responsible for the primary pathology in affected shrimp. Since the causative agent has been identified, we propose a new name for EMS as Acute Hepatopancreatic Necrosis Disease (AHPND). Characterizations of the AHPND-causing Vibrio parahaemolyticus: Biochemical methods and molecular methods were used. Based on these results, various diagnostic methods were developed including polymerase chain reaction (PCR) test and biochemical tests. Other aspects of the AHPND causing V. parahaemolyticus were also run to determine such as antibiogram and the development of resistance mechanism of the bacteria exposed to farm conditions with antibiotic medications, pathogenicity, and infection dose of the bacteria, mode of infection, mechanisms governing the toxin production, and effects of environmental parameters on the invasion of the agent. Some proposed control measures for AHPND: Several antibiotic-free approaches were tested to determine viable control methods for AHPND. The principle proposed control method is to increase biosecurity. With the PCR method that has been developed, potential sources of the pathogen such as post-larvae and broodstock can be tested. As more and more insights of the pathogen were explored, the behavior of the pathogen was further elucidated. Based on this, control methods such as using polyculture with tilapia, probiotics, and bioflocs system were also tested. Several improvements in shrimp farming practices that may reduce the outbreak of the disease were also proposed.

Prebiotics and probiotics, proposed alternatives to antibiotics in shrimp aquaculture, are reported to improve growth parameters, promote disease resistance, and influence the gut microbial community. This study aimed to investigate the influence of prebiotic- or probiotic-coated feed and/or exposure to the Early Mortality Syndrome-causing strain of Vibrio parahaemolyticus ( VP-EMS) on the mid and hindgut microbiome of Pacific white shrimp (Litopenaeus vannamei). A monoculture probiotic strain of Bacillus subtilis spores: O14VRQ, and a prebiotic product of cultured Saccharomyces cerevisiae cell walls: MOS, were administered to shrimp as feed additives for 14 days, before a pathogen challenge to VP-EMS. Based on previous efforts, animals in this study were fed experimental diets for 14 days to allow ample amount of time for the prebiotic to be metabolized by health-promoting bacteria and for the probiotic spores to germinate. The pathogen challenge consisted of negative disease control (no VP-EMS exposure, commercial feed), positive disease control (VP-EMS exposure, commercial feed) and two treatment groups, probiotic (VP-EMS exposure) and prebiotic (VP-EMS exposure). DNA extraction, 16S rRNA gene amplicon sequencing, polymerase chain reaction (PCR), and sequencing were utilized to create an overview of the mid and hindgut microbial composition. No significant differences in survival were shown between experimental diets following exposure to sublethal levels of VP-EMS. Bioinformatic analyses revealed no distinct shifts in the mid and hindgut microbiome of shrimp across experimental diets and time points. Results of this data revealed that dominant members of the intestinal microbiome, Proteobacteria, Actinobacteriota, Bacteroidota, Verrucomicrobiota, Flavobacteriaceae, Demequinaceae, Vibrionaceae, Shewanellaceae, Rhodobacteriaceae, and Rubritaleaceae were relatively stable across treatments and time points. Sequencing methods such as metagenomics or metatranscriptomics should be utilized for a higher microbiome resolution. Furthermore, the use of quantitative polymerase chain reaction to quantify ingested probiotic spores, prebiotic-associated bacteria, and VP-EMS is recommended. / Master of Science in Life Sciences / Shrimp aquaculture is one of the fastest-growing aquaculture sectors that provides another supply of feed that save wild fish populations. The use of prebiotics and probiotics are reported to improve growth, provide disease protection, influence the gut community, improve the immune system, and serve as substitutes to antibiotics. In this study, the effect of probiotic-, or prebiotic-coated diets and/or exposure to the Early Mortality Syndrome-causing Vibrio parahaemolyticus (VP-EMS) strain on the gut communty of shrimp (Litopenaeus vannamei) was investigated. DNA extraction, 16S rRNA gene amplification, and sequencing were utilized to identify the microbes in the intestines of shrimp. Based on previous studies, animals in this study were fed experimental diets for 14 days to allow enough time for prebiotic-associated bacteria and probiotic spores to multiply within the intestines. Exposure to a sublethal level of VP-EMS did not significantly affect shrimp survival between treatments. Analyses showed no noticeable differences in the intestinal microbial communities between treatments and time points. This research provided initial proof of what microbes occupy the mid and hindgut microbiome. A higher resolution sequencing method is recommended to gain a better understanding of the microbes and their roles in the intestines. The use of quantitative polymerase chain reaction is warranted to evaluate the amount of ingested probiotic spores, prebiotic-associated bacteria, and VP-EMS.