Location: Warmwater Aquaculture Research Unit2010 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
Preliminary bacterial challenges have been conducted comparing mortality of fish fed bactericidal and bacteriostatic antibiotics before and after exposure to Edwardsiella (E.) ictaluri indicate bactericidal drug was shown more effective in treating infection but could interfere with the development of acquired immunity if used prior to infection. Anticoccidial drugs were evaluated as a potential treatment for proliferative gill disease. Before and after exposure to Henneguya ictaluri actinospores. fish readily consumed diets containing 100 mg/kg amprolium but not diets containing 60 mg/kg salinomycin. Amprolium was not shown effective in reducing acute stages of disease, however, it is anticipated that it will interfere with the developing life stages associated with chronic H. ictaluri infection. Preliminary studies indicate smallmouth buffalo (SMB) may be effective for biological control of benthic oligochaetes, which transmit myxozoan parasites, including the causative agent of proliferative. SMB were shown to completely eliminate benthic organism from pond sediments whereas, environments without SMB contained diverse populations of benthic organisms, including several species of benthic oligochaetes. 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 immunoglobulin type M (IgM). The specificity of the 9E1 for IgM from a blue catfish and blue catfish hybrids is unknown. Preliminary results indicate that 9E1binds equally with the IgM antibodies of blue and blue x channel hybrid catfish and can be used in blue and hybrid catfish to asses humoral immunity to key catfish pathogens. Primer and probe combinations have been developed for specific amplification for E. ictaluri, Flavobacterium columnare, Bolbophorus (B.) damnificus and H. ictaluri. 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. Toxin-free ELISA procedure was developed to measure the level of anti-BoNT/E antibody in catfish sera. A peptide library was constructed based on the known primary structure of the heavy chain subunit of BoNT/E. Archived channel catfish sera collected from fish exposed to BoNT/E was screened for antibody binding with a panel of 69 synthetic peptides composed of 18 amino acid residues. Peptides with highly reactive epitopes will be used as primary antigens to optimize ELISA conditions. Studies were initiated to evaluate the effects of mycotoxin contaminated feed on growth and disease resistance of catfish. Corn naturally contaminated with aflatoxin was used to formulate diets to contain graded toxin concentrations ranging from 0 to 160 ug/kg feed. No differences in mean weight gain and mortality following disease challenge were observed among treatments. These results are in agreement with other studies conducted in our laboratory showing catfish are resistant to relatively high levels of aflatoxin.
5. Significant Activities that Support Special Target Populations
It is estimated that disease-related mortalities account for 45-50% of all losses incurred on farms and may account for as much as $100 million annually in direct economic impact. Production inefficiencies related to management and disease losses disproportionately affect small farms because they are more susceptible to economic impacts related to interruption of cash flows. The USDA Census of Aquaculture conducted in 2000 classified 84% of catfish farms as small businesses, with annual sales of less than $500,000. Of the 1,370 catfish farms in the United States, 38% (515) reported annual revenues of less than $25,000. The profitable operation of small farms is dependent on improvements in disease management to curtail monetary losses associated with disease. Catfish health research provides technical and diagnostic support to catfish farmers and assists with the implementation and evaluation of disease treatments and management strategies. Specific activities include diagnostic evaluations, disease monitoring programs, research to support the approval and licensing of new aquatic animal vaccines and medicines, and development of fish health management protocols for improving production efficiency.
Khoo, L., Rommel, F.A., Smith, A.A., Griffin, M.J., Pote, L.M. 2010. Myxobolus Neurophilus: Morphologic, Histopathologic and Molecular Characterization. Diseases of Aquatic Organisms. 89:51-61.