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Research Project: Health Management, Disease Prevention and Control Strategies in Catfish Aquaculture

Location: Warmwater Aquaculture Research Unit

Project Number: 6066-31320-004-00-D
Project Type: In-House Appropriated

Start Date: Dec 14, 2014
End Date: Dec 13, 2019

1) Investigate new and emerging diseases, and develop rapid diagnostic procedures for important pathogens of channel, hybrids and blue catfish. Subobjective 1.1 Use diagnostic case submissions to identify changes in disease prevalence and emergence of new diseases. Subobjective 1.2 Develop molecular diagnostic tests for simultaneous detection of multiple catfish pathogens. This objective is non-hypothesis driven and serves as an essential component of the disease surveillance programs and helps define clinical and applied research programs that address critical fish health issues facing the catfish industry. This research will aim to determine whether molecular markers can be used to identify multiple pathogens in a single PCR reaction. 2) Study the pathology and epidemiology of significant pathogens affecting cultured catfish. Subobjective 2.1 Evaluate the susceptibility and pathology of catfish to Edwardsiella spp. Subobjective 2.2 Evaluate the pathology of Drepanocephalus spathans in channel catfish. This research will determine whether blue, channel, and blue x channel catfish hybrids have varying degrees of susceptibility to Edwardsiella tarda, Edwardsiella piscicida, and Edwardsiella piscicida–like spp and determine whether the metacercariae stage of the digenetic trematode Drepanocephalus spathans is short lived (< 6 months) in channel catfish. 3) Investigate the responses of channel, hybrid and blue catfish to therapeutic agents and oral vaccines for important bacterial pathogens. Subobjective 3.1 Evaluate susceptibility of archived and clinical bacterial isolates to antimicrobials, and correlate antimicrobial susceptibility with treatment efficacy. Sub-objective 3.2 Determine the optimal age for vaccinating catfish against ESC using an oral attenuated E. ictaluri vaccine. Subobjective 3.3 Determine if certain stressors will affect vaccine efficacy and safety of catfish orally vaccinated with an attenuated ESC vaccine. Subobjective 3.4 Evaluate mortality resulting from exposure of vaccinated fish to archived and year-end E. ictaluri isolates. Data will establish uniform standardized interpretive criteria that can be used by all aquatic laboratories that are involved with clinical disease diagnosis of catfish. The research will also examine whether antimicrobial susceptibilities determined by minimum inhibitory concentration and zone diameters of inhibition will affect the treatment efficacy of medicated feeds. 4) Develop and implement practical management strategies to improve fish health and production efficiency. Subobjective 4.1 Evaluate effects of hybrid catfish production on incidence and prevalence of Henneguya ictaluri in catfish ponds. Subobjective 4.2 Field evaluation of an oral ESC vaccination platform for control of E. ictaluri infections in catfish. This research will determine if the production of hybrid catfish reduces the incidence and severity of proliferative gill disease, caused by the myxozoan parasite H. ictaluri, in catfish ponds and whether oral vaccination will improve survival and production efficiency of channel catfish raised under commercial conditions.

Diagnostic records provide critical insight to changes in disease trends and emergence of new diseases affecting animal production systems, an essential component of population health management. This information provides clinicians, caregivers and researchers a good cross-section of disease occurrence across the industry. This information can then be used to prioritize the allocation of resources in the development of rapid diagnostic procedures, disease surveillance and treatment programs and implementation of biosecurity measures to stop the spread of emerging diseases when possible. Edwardsiella tarda has been identified as an emerging disease as indicated by diagnostic case submissions and interaction with industry advisory groups. Recently, E. tarda has undergone a reclassification, suggesting many organisms previously thought to be E. tarda are actually E. piscicida, a newly described fish pathogen closely related to E. ictaluri. Research will focus on the comparative susceptibility of channel catfish, blue catfish and hybrid catfish to E. piscicida, E. tarda and the as yet classified E. piscicida-like sp. In addition, quantitative PCR assays will be developed to detect and quantify these various pathogens in fish tissues and the pond environment. Non-hypothesis driven clinical research will be conducted to define minimum inhibitory concentration (MIC) and cut-off values for clinical bacterial pathogens against 3 commercially available antimicrobials. This information is critical to policy review concerning antibiotic approval in the catfish industry. Separately, hypothesis-driven research will be conducted to optimize the effectiveness of oral vaccination and determine environmental factors which may limit efficacy and safety. Field studies will be conducted to evaluate practical management strategies for controlling two diseases which account for more than half of the diagnostic case submissions to the Aquatic Research and Diagnostic Laboratory (ARDL). Research will focus on development management strategies for controlling proliferative gill disease, caused by the myxozoan parasite Henneguya ictaluri and field evaluation of an oral vaccine for control of enteric septicemia of catfish (ESC) caused by the gram-negative bacteria Edwardsiella ictaluri. These management approaches have the potential to greatly reduce the impact of these diseases, that are estimated to cost the catfish industry $60-80 million annually.