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United States Department of Agriculture

Agricultural Research Service

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Location: Warmwater Aquaculture Research Unit

2012 Annual Report

1a. Objectives (from AD-416):
Objective 1: Monitoring and surveillance of biotoxin, pathogen, pathogen/host interactions in aquatic environment. Objective 2: Develop methods to protect channel catfish and its hybrids with vaccines, antibiotics and other therapeutics against enteric septicemia of catfish, columnaris, proliferative gill disease, botulism, Bolbophorus and anemia. Objective 3: Effects of chemical and mycotoxin feed contaminants on growth and disease resistance of catfish.

1b. Approach (from AD-416):
Despite successful growth and prosperity of the past few decades, the U.S. catfish industry is threatened by increasing disease losses, low fish prices, high feed costs and foreign competition. Fish losses due to disease are estimated to cost the U.S. catfish industry $100 million in direct sales annually and are considered the largest impediment to increasing production efficiencies. Objective 1 will provide catfish farmers a better method to monitor biotoxins, pathogens, and pathogen/host interaction in the aquatic environment using new and better surveillance and monitoring procedures coupled with the development of experimental vaccines. Case submissions will also document the prevalence and the emergence of new diseases in the catfish industry. Objective 2 will develop new methods to protect catfish against known disease organisms including antibiotics and vaccines and evaluate the effectiveness of these products to improve disease resistance. New and improved on-farm management programs for the control of trematode infections will be developed. Objective 3 will investigate the prevalence of chemical and mycotoxin feed contaminants in fish feeds and develop methods to detect and control feed contaminants that affect disease resistance of catfish. The overall benefits of this project will be to improve fish health reduce losses due to infectious and non-infectious diseases. The reduction of losses to disease will make catfish farming a more profitable endeavor and increase the competitiveness of U.S. aquaculture.

3. Progress Report:
In 2011, the Aquatic Research & Diagnostic Laboratory saw a total of 852 cases of which 599 were cases submitted by producers. In addition, a total of 1,060 water quality samples were submitted and analyzed. With regards to antibiotic resistance, there were no resistant isolates seen in the over 400 bacterial isolates cultured. Only 1 of 191 isolates of Edwardsiella (E.) ictaluri and 2 out of 19 isolates of Edwardsiella tarda had intermediate sensitivities. Oral vaccination of fish with an attenuated E. ictaluri vaccine was shown very effective in preventing mortality associated with enteric septicemia of catfish. The vaccine was shown to negate the need for medicated feeds to control mortality. Preliminary studies indicated smallmouth buffalo (SMB) may be an effective agent for biological control of benthic oligochaetes, which transmit myxozoan parasites, including the causative agent of proliferative gill disease. Ponds stocked with juvenile SMB (2-3”) had significantly lower oligochaete populations compared to ponds without SMB. Primer and probe combinations have been developed for specific amplification for Edwardsiella ictaluri, Flavobacterium (F.) columnare, Bolbophorus (B.) damnificus and Henneguya (H.) ictaluri and an emerging, highly virulent strain of Aeromonas hydrophila. A similar assay for E. tarda is being developed. Assays for H. ictaluri, B. damnificus and E. ictaluri have been validated and will be used to evaluate infections rates and integrated into field monitoring programs. Assessment of antigen specific antibody levels in channel catfish is based on a detection system employing a mouse monoclonal antibody (9E1) developed against channel catfish immunoglobulinm (IgM). Validation studies show 9E1 binds equally with IgM antibodies of blue and blue x channel hybrid catfish. Immunoassays assessing humoral immunity in blues and hybrids have been developed to key catfish pathogens. The LD50 for botulinum type-E toxin (BoNT/E) was determined to establish vaccination/challenge protocols for catfish. The 96 hour LD50 for 5.3 grams channel catfish was determined to be 13.7 pico grams (pg). Immunization trials with recombinant heavy chain BoNT/E have been conducted to hyper-immunize channel catfish to create a reference serum to determine optimal antigen coating concentrations for enzyme-linked immunosorbent assay (ELISA). Based on endpoint titers, generated from hyper-immunized fish (IP injection), the recombinant antigen appears poorly immunogenic. Studies have been conducted evaluating the effects of mycotoxin contaminated feed on growth and disease resistance of catfish. Catfish fed diets formulated with alfatoxin contaminated feed showed alfatoxin levels of up to 160 ug/kg feed had no effect on growth or disease resistance. Similar results were also observed in catfish fed diets containing elevated levels of deoxynivalenol (DON) toxin.

4. Accomplishments

Review Publications
Khoo, L.H., Goodwin, A.E., Wise, D.J., Holmes, W.E., Hanson, L.A., Steadman, J.M., Mcintyre, L.M., Gaunt, P.S. 2011. The pathology associated with visceral toxicosis of catfish. Journal of Veterinary Diagnostic Investigation. 23(6):1217-1221.

Gaunt, P.S., Gao, D.X., Wills, R. 2011. Preparation of ormetoprim-sulfadimethoxine-medicated discs for disc diffusion assay. North American Journal of Aquaculture. 73:17-20.

Griffin, M.J., Goodwin, A.E. 2011. Theohanellus toyamai infecting the gills of Koi cyprinus carpio in the Eastern United States. Journal of Parasitology. 97(3):493-502.

Griffin, M.J., Mauel, M.J., Greenway, T.E., Khoo, L.H., Wise, D.J. 2011. A real time polymerase chain reaction assay for quantification of Edwardsiella ictaluri in catfish pond water and genetic homogeneity of diagnostic case isolates from Mississippi. Journal of Aquatic Animal Health. 23(4):178-188.

Gaunt, P.S., Langston, C., Wrzesinski, C.L., Gao, D., Adams, P., Couch, L.S. 2011. Single intravenous and oral dose pharmacokinetics of florfenicol in the channel catfish Ictalurus punctatus. Journal of Veterinary Pharmacology and Therapeutics. P.1365-2885.

Last Modified: 10/20/2017
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