2012 Annual Report 1a.Objectives (from AD-416): The objective of this cooperative research project is to discover and develop novel natural antimicrobial peptides that could be used to control fish diseases. This research project will allow USDA, Agricultural Research Service and Qingdao Agricultural University (QDAU) to implement cooperative research with a common goal to discover and develop novel natural antimicrobial peptides to control fish bacterial diseases. The fish pathogens to be investigated include but not limited to Edwardsiella ictaluri, Streptococcus iniae, and Flavobacterium columnare. 1b.Approach (from AD-416): Antimicrobial peptides will be isolated through bioassay-guided fractionation that shows activity against important fish bacterial pathogens such as, but not limited to, Edwardsiella ictaluri, Streptococcus iniae, and Flavobacterium columnare. The source of antimicrobial peptides will be aquatic animals, such as bivalves, from which a novel antimicrobial peptides has been discovered by Qingdao Agricultural University. Bioactive crude protein extracts will be initially tested for antimicrobial activity against fish pathogens. Various fractionation techniques, including HPLC, will be used to separate, purify, and determine the active antimicrobial ingredient guided by antimicrobial bioassays. 3.Progress Report: The objective of this cooperative research project is to discover and develop novel natural antimicrobial diseases in aquatic animals. Using quantitative polymerase chain reaction (PCR) technique, the relative transcriptional levels of seven channel catfish antimicrobial peptide (AMP) genes in response to acute infection of Edwardsiella (E.) ictaluri, has been determined by ARS scientists in Auburn, AL. Among all the AMPs that were significantly upregulated at different time points, hepcidin at 4-, 6-, and 12-h post infection was upregulated the most. In vitro growth studies revealed that the presence of synthetic hepcidin peptide at concentration of 80 micromolar or higher significantly inhibited the growth of E. ictaluri. This work suggests that AMP might be used for the control of fish diseases.