Location: Warmwater Aquaculture Research Unit2013 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:
A mechanized system for mixing and delivering a live attenuated oral vaccine was developed in collaboration with United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Poultry Unit, and Mississippi State University. Protocols for the commercial production of a live attenuated oral enteric septicemia of catfish (ESC) vaccine was developed in collaboration with USDA-ARS-National Biological Control Laboratory. Vaccine field trials conducted with the developed technologies showed excellent protection from disease and negated the need for medicated feeds. Field trials showed smallmouth buffalo did not alter oligochaete populations, intermediate host for proliferative gill disease, or reduce actinospore levels in pond water. As a result SMB are no longer recommended as a biological control for this disease. Increased pressure from the American white pelican has resulted in wide spread debilitating trematode infections on a majority of farms. Disease treatment regiments, developed from this project, have been implemented and were shown effective in controlling the intermediate host of the parasite. Real-time polymerase chain reactions (PCR) were developed to detect the trematode Bolbophorus damnificus in fish tissues and pond water. The assay differentiates between two morphologically similar pathogenic and non-pathogenic species of Bolbophorus and is critical to scientific studies. Development of real-time PCR assays for catfish pathogens led to the reclassification of Edwardsiella (E.) tarda. Further research identified this fish pathogen as E. piscicida, a newly described pathogen from fish. Assays for the detection of Flavobacterium columnare, E. tarda, E. piscicida and E. piscicida-like species are being validated. Work has been initiated into the development of a diagnostic PCR assay for the identification of the digenetic trematode Drepanocephalus spathans, a parasite of the double crested cormorant, and shown to be infective to channel catfish. In addition, work has also been initiated into the development of a discriminatory PCR assay for the identification of an unidentified echinostomatid cercaria, demonstrated to be infective to catfish. In 2012, the Aquatic Research & Diagnostic Laboratory received a total of 772 cases of which 635 were submitted by producers which is an increase from the previous year (599 cases) despite the contraction of the channel catfish industry. There were no antibiotic resistant isolates out of the 363 bacterial isolates cultured. Botulism Type E (BoNT/E) was identified as the causative agent of visceral toxicosis of catfish (VTC). Solid phase ELISA assays for the detection of anti-BoNT/E antibody were developed against recombinant peptide sequences of the heavy chain toxin. Antibody from convalescent fish showed low specificity to the peptide sequences employed in the assay. Fish immunized with a recombinant heavy chain (BoNT/E) yielded weak and negligible antibody responses and offered no protection following exposure to the toxin. The toxin was successfully inserted in channel catfish virus (CCV) and the recombinant BoNT/E CCV will be evaluated as a potential vaccine.
Soto, E., Griffin, M., Wiles, J., Hawke, J. 2012. Genetic analysis and antimicrobial susceptibility of Francisella noatunensis subsp. orientalis (sun. F. asiatica) isolates from fish. Veterinary Microbiology. 154:407-412.