Theses and Dissertations

ORCID

https://orcid.org/0000-0002-7332-1361

Issuing Body

Mississippi State University

Advisor

Hanson, Larry A.

Committee Member

Beck, Benjamin H.

Committee Member

Lawrence, Mark L.

Committee Member

Posadas, Benedict C.

Committee Member

Williams, Lynda B.

Date of Degree

12-13-2024

Original embargo terms

Worldwide

Document Type

Dissertation - Open Access

Major

Veterinary Medical Science

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Veterinary Medicine

Department

Department of Comparative Biomedical Sciences

Abstract

In 2014, a virulent clonal group of Aeromonas hydrophila (VAH) was the predominant disease impacting the east Mississippi (EMS) commercial catfish industry. The EMS aquatic ambulatory service observed an area not prone to VAH outbreaks. In addition, frequent underestimations of the scope and economic impact of the EMS catfish industry and its diseases warranted a descriptive effort. Therefore, the EMS catfish industry, its economic impact, the diseases of this region and their economic impact were described. Further, differences in water and geological chemistry of the area not prone to VAH outbreaks, and the sensitivity of VAH and Edwardsiella ictaluri to any of those differences were evaluated. A survey of EMS catfish producers documented 115 commercial operations (4,900 ha) with a mean catfish production of 8,070 ± 783 kg ha-1. The direct ($100.2M), indirect ($15.7M) and induced ($54.9M) economic impacts of east MS totaled $170.8M, which generated $18.5M in state and federal tax revenues. The predominant diseases reported by producers were parasites (Bolbophorus damnificus and Henneguya spp.), VAH, and Flavobacterium spp. The direct (-$16.6M), indirect (-$2.6M), and induced (-$10.9M) economic impacts of disease in east MS totaled -$30.1M. The occurrence of these diseases results in a loss of $3.3M in state and federal tax revenues. Differences in disease prevalence were observed regionally and between the east MS producer and a regional diagnostic lab. Iron (mg l-1) was the only significantly different water quality parameter measured among the farms that were less (3.8x) prone to MAS outbreaks (0.61 ± 0.3) versus the remainder of the EMS industry (0.22 ± 0.14). Pyrite (FeS2) and kaolinite (Al2Si2O5(OH4) were characteristic mineralogical features of the farms not prone to MAS outbreaks. In-vitro sensitivity analyses demonstrated the bactericidal properties of iron sulfate, a mixture of iron sulfate + aluminum sulfate and kaolin clay to VAH and E. ictaluri. Survival in VAH immersion challenges was higher among catfish fed diets supplemented with iron sulfate, kaolin, iron sulfate + kaolin and iron sulfate + aluminum sulfate. There were no differences observed in survival among the E. ictaluri in-vivo challenge treatments and controls

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