Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Colvin, Michael

Committee Member

Wise, David

Committee Member

Walker, Ryan

Committee Member

Greenway, Terrence

Committee Member

Griffin, Matthew

Other Advisors or Committee Members

Mischke, Charles

Date of Degree

8-1-2020

Original embargo terms

Visible to MSU only for 2 years

Document Type

Dissertation - Campus Access Only

Major

Forest Resources

Degree Name

Doctor of Philosophy

College

College of Forest Resources

Department

Department of Wildlife, Fisheries and Aquaculture

Abstract

Commercial catfish production is an inveterate industry within the southeastern United States. Bacterial disease is a significant detriment to global aquaculture, including the United States catfish industry. Among them, an atypical strain of the bacterium Aeromonas hydrophila has plagued the industry since the late 2000s. Atypical A. hydrophila (aAh) outbreaks are largely acute, resulting in catastrophic losses. The disease ecology, prevalence, and genetic distribution are poorly understood. Atypical Aeromonas hydrophila displays a rapid onset with few warning signs of the impending disease, making it difficult for early detection. At present there are two recognized haplotypes of aAh. This project aimed to investigate changes in the spatial and temporal distributions of these haplotypes. The analysis of clinical isolates from different geographic regions across multiple years revealed complete supplanting by the younger haplotype in the Mississippi Delta within 5 years of first isolation. Comparative genomics demonstrated distinct divergences in specific virulence components between the two strains, specifically the Type VI Secretion System, which may explain putative differences in outbreak dynamics and recent displacement of one strain by the other. Also, a rapid, non-lethal screening method was validated that can detect aAh within the catfish host. This method affords data collection regarding infection severity prior to onset of disease and, can predict aAh prevalence at the fish- and pond-levels. The occupancy model indicates more than half the population within a pond may be infected with aAh despite no overt signs of disease. Additionally, aAh is commonly present in approximately 10% of the population, providing the first evidence of a carrier state in this disease. Lastly, a compartmental SLIR model was used to investigate disease dynamics of aAh in catfish aquaculture ponds. Simulations suggest the introduction hypothesis does affect estimated pond profit and antibiotic intervention is an economical treatment for aAh. Routine monitoring was less economical and could dramatically reduce profit in some scenarios. Overall, this work expands our current knowledge of aAh in catfish aquaculture and lays the foundation for future studies investigating aAh management and mitigation of bacterial disease in catfish aquaculture.

URI

https://hdl.handle.net/11668/18435

Sponsorship

National Institute of Food and Agriculture (award number 2017-67015-26794); U.S. Department of Agriculture (project number MIS‐371530); the U.S. Department of Agriculture Agricultural Research Service–Catfish Health Initiative

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