Epidemiology and economic impact of disease-related losses on commercial catfish farms: a seven-year case study from Alabama, USA

Authors: ABDELRAHMAN, HISHAM - Auburn University; HEMSTREET, WILLIAM - Auburn University; ROY, LUKE - Auburn University; HANSON, TERRILL - Auburn University; Beck, Benjamin; KELLY, ANITA - Auburn University

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2022
Publication Date: 12/25/2022
Citation: Abdelrahman, H.A., Hemstreet, W.B., Roy, L.A., Hanson, T.R., Beck, B.H., Kelly, A.M. 2022. Epidemiology and economic impact of disease-related losses on commercial catfish farms: a seven-year case study from Alabama, USA. Aquaculture. 566:739206. https://doi.org/10.1016/j.aquaculture.2022.739206.
DOI: https://doi.org/10.1016/j.aquaculture.2022.739206

Interpretive Summary: Alabama ranks second in US food-size catfish production. The Alabama Fish Farming Center (AFFC) Diagnostic Laboratory has documented many catfish diseases in west Alabama (AL), where most commercial catfish production occurs in the state. The primary diseases resulting in significant catfish losses as reported by the AFFC include hypervirulent Aeromonas hydrophila (vAh), Edwardsiella ictaluri, Bolbophorus damnificus, columnaris disease, proliferative gill disease (PGD), releases of algal toxins, Ichthyophthirius multifiliis, and other non-disease related factors. The objectives of this study were to determine statewide production losses caused by diseases, identify the most incident catfish diseases affecting AL farm-raised catfish production in freshwater ponds and their annual pattern, and determine disease-related economic impacts. The AFFC conducted seven annual questionnaire surveys of AL catfish farmers since 2015 to assess the epidemiological situation of farm-raised catfish fish diseases and their economic impacts. Across the study (2015–2021), the annual number of survey respondents ranged from 64–74, with a total of 482 respondents. The annual survey coverage area ranged from 6,410–7,006 ha/year. About 97% of survey coverage area reported fish losses caused by a disease. Fish diseases resulted in the loss of 9 million fish/year (2.9 million kg/year; 436.7 kg/ha/year). Bacterial diseases resulted in >83% of catfish disease losses (>5 times losses to non-bacterial causes). The most incident statewide catfish disease was vAh (225 kg/ha/year), followed by columnaris (140 kg/ha/year), followed by Edwardsiella (52 kg/ha/year). The temporal epidemiological analysis results indicate that annual trends of vAh losses were correlated with high maximum daily temperatures. In contrast, annual trends of PGD and Bolbophorus were correlated with prolonged precipitation periods and total quantity of rainfall, respectively. Economic losses caused by fish losses to bacterial diseases, non-bacterial diseases, production losses due to reduced feeding during outbreaks, and expenditures associated with catfish diseases were responsible for 54.5%, 10.8%, 22.0%, and 12.7% of total direct economic impacts attributed to AL farm-raised catfish industry, respectively. Total disease-related financial losses in west AL were 11.1 million USD/year (1,651 USD/ha/year), representing about 9.5% of food-size catfish sales in AL. The present study provides the first comprehensive assessment of epidemiology and health economics of farm-raised catfish disease in the freshwater pond environment for a substantial duration. More studies focusing on disease losses at the county- and farm-level would provide useful information regarding the spatial epidemiology of diseases and their underlying risk factors.

Technical Abstract: Alabama ranks second in US food-size catfish production. The Alabama Fish Farming Center (AFFC) Diagnostic Laboratory has documented many catfish diseases in west Alabama (AL), where most commercial catfish production occurs in the state. The primary diseases resulting in significant catfish losses as reported by the AFFC include hypervirulent Aeromonas hydrophila (vAh), Edwardsiella ictaluri, Bolbophorus damnificus, columnaris disease, proliferative gill disease (PGD), releases of algal toxins, Ichthyophthirius multifiliis, and other non-disease related factors. The objectives of this study were to determine statewide production losses caused by diseases, identify the most incident catfish diseases affecting AL farm-raised catfish production in freshwater ponds and their annual pattern, and determine disease-related economic impacts. The AFFC conducted seven annual retrospective questionnaire surveys of AL catfish farmers since 2015 to assess the epidemiological situation of farm-raised catfish fish diseases and their economic impacts. Across the study (2015–2021), the annual number of survey respondents ranged from 64–74, with a total of 482 respondents. The yearly survey response rate ranged from 95.6–100% (mean: 98.2%). The annual survey coverage area ranged from 6,410–7,006 ha/year. About 97% of survey coverage area reported fish losses caused by a disease. Fish diseases resulted in the loss of 9 million fish/year (2.9 million kg/year; 436.7 kg/ha/year). Bacterial diseases resulted in >83% of catfish disease losses (>5 times losses to non-bacterial causes). The most incident statewide catfish disease was vAh (225 kg/ha/year), followed by columnaris (140 kg/ha/year), followed by Edwardsiella (52 kg/ha/year). The temporal epidemiological analysis results indicate that annual trends of vAh losses were correlated with high maximum daily temperatures. In contrast, annual trends of PGD and Bolbophorus were correlated with prolonged precipitation periods and total quantity of rainfall, respectively. Economic losses caused by fish losses to bacterial diseases, non-bacterial diseases, production losses due to reduced feeding during outbreaks, and expenditures associated with catfish diseases were responsible for 54.5%, 10.8%, 22.0%, and 12.7% of total direct economic impacts attributed to AL farm-raised catfish industry, respectively. Total disease-related financial losses in west AL were 11.1 million USD/year (1,651 USD/ha/year), representing about 9.5% of food-size catfish sales in AL. The present study provides the first comprehensive assessment of epidemiology and health economics of farm-raised catfish disease in the freshwater pond environment for a substantial duration. More studies focusing on disease losses at the county- and farm-level would provide useful information regarding the spatial epidemiology of diseases and their underlying risk factors.