IN THE CHANNEL CATFISH AQUACULTURE INDUSTRY, WE OFTEN SEE UNEXPLAINED PATTERNS OF OUTBREAKS OF INFECTIOUS DISEASES. CATFISH AQUACULTURE IS AN INTENSIVE, CONTINUOUS POND BASED OPERATION. THE PRODUCTION PONDS ARE RARELY COMPLETELY HARVESTED. THEREFORE, MOST POPULATIONS ARE ENDEMIC FOR COMMON INFECTIOUS PATHOGENS OF CATFISH. THE COMMONLY ASSUMED DISEASE MODEL IS AN ENVIRONMENTAL STRESSOR CAUSES IMMUNOSUPPRESSION AND THIS ALLOWS THE PATHOGEN GAIN A FOOTHOLD AND CAUSE DISEASE. YET, A LARGE PORTION OF THE INFECTIOUS DISEASE OUTBREAKS WE SEE ARE NOT TIED TO AN OBVIOUS STRESSING EVENT. WE BELIEVE THAT THE DIRECT INFLUENCE OF BIOTOXINS ARE UNDERLYING PREDISPOSING FACTORS FOR THESE DISEASE OUTBREAKS. IN THIS GRANT, WE FOCUS ON MICROCYSTIN LR. THIS TOXIN IS COMMONLY PRODUCED BY CYANOBACTERIA (BLUE-GREEN ALGAE) WHICH ARE PREVALENT IN CATFISH PRODUCTION PONDS. THE MECHANISM OF ACTION OF MICROCYSTIN LR INCLUDES LIVER TOXICITY AND POTENTIAL SUPPRESSION OF FUNCTION IN CELLS OF THE INNATE IMMUNE SYSTEM. OUR STUDY WILL EVALUATE THE PHYSIOLOGICAL RELEVANCE OF THE LEVELS OF MICROCYSTIN FOUND IN CATFISH FROM PRODUCTION PONDS AND THE IMPACT OF THIS ON DISEASE SUSCEPTIBILITY. THE FIRST PART OF THIS STUDY WILL BE CONDUCTED BY DOSING FISH WITH MICROCYSTIN LR AND EVALUATING THE LEVELS OF TOXIN THAT OCCURS IN THE TISSUES AND THE ASSOCIATED PATHOLOGY PHYSIOLOGICAL CHANGES AND CHANGES IN IMMUNE SYSTEM FUNCTION. THE SECOND PART OF THE STUDY WILL BE PERFORMED BY DOSING THE FISH WITH MICROCYSTIN-LR AND DETERMINING THE DEGREE TO WHICH THE TOXIN CHANGES THE CATFISH'S SUSCEPTIBILITY TO TWO COMMON BACTERIAL DISEASE THAT OCCUR PRIMARILY DURING THE HOT SUMMER MONTHS WHEN MICROSCYSTIN LR PRODUCING ALGAE ARE MOST PREVALENT. BY DOING THIS RESEARCH, WE WILL BE ABLE TO EVALUATE THE NEED TO INCORPORATE ANALYSIS OF THIS TOXIN INTO OUR DISEASE DIAGNOSTIC LABORATORIES AND TO ASSIST FARMERS IN DISEASE MANAGEMENT DECISIONS. IN ADDITION TO STANDARD ROUTES OF DISSEMINATING SCIENTIFIC FINDING, WE PLAN TO PRESENT OUR FINDINGS DIRECTLY TO THE PRODUCERS IN ANNUAL WORKSHOPS AND TO OTHER DIAGNOSTICIANS IN FISH HEALTH MEETINGS.