**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** INTENSIVE AQUACULTURE MAY NEGATIVELY IMPACT FISH HEALTH AND WELL-BEING. DAILY AQUACULTURE PRACTICES IMPOSE STRESSORS OF MANY KINDS INCLUDING PHYSICAL, BIOLOGICAL AND CHEMICAL. EXAMPLES OF MAN-GENERATED STRESSORS IN AQUACULTURE ARE OVER-CROWDING, TRANSPORTATION AND MANUAL HANDLING FOR VACCINATION. AMONG THE ENVIRONMENTAL STRESSORS, TEMPERATURE IS ONE OF THE MOST PROMINENT AND WELL-KNOWN FACTORS INFLUENCING FISH PERFORMANCE IN AQUACULTURE. SINCE FISH ARE COLD-BLOODED ANIMALS, THEIR PHYSIOLOGICAL MECHANISMS ARE GREATLY INFLUENCED BY ENVIRONMENTAL TEMPERATURE CHANGES. THESE PRACTICES CAN THEREFORE REDUCE FISH GROWTH, REDUCE MARKET PRODUCT QUALITY, IMPAIR IMMUNITY AND INCREASE DISEASE SUSCEPTIBILITY RESULTING IN A REDUCTION IN THE SUSTAINABILITY OF THE FISH FARMING INDUSTRY. TO LIMIT ALL OF THESE LOSSES, ANTIBIOTICS AND CHEMOTHERAPEUTANTS ARE LARGELY USED TO PREVENT AND CURE FISH DISEASES, YET THESE COMPOUNDS ARE STRICTLY REGULATED FOR THEIR POTENTIAL TOXICITY ON FISH, IMPACTS ON ENVIRONMENTAL HEALTH AS WELL AS HUMAN HEALTH. ONE OF THE REASONS WHY STRESS IS DETRIMENTAL FOR FISH HEALTH IS ITS IMPACT ON MUCOSAL HEALTH. STRESS CAN REDUCE MUCOSAL IMMUNE DEFENSES IN FISH AND DISTURB THE BENEFICIAL MICROBIOTA. AMONG THE KEY PLAYERS IN MUCOSAL HEALTH OF ALL ANIMALS ARE ANTIMICROBIAL PEPTIDES SUCH AS BETA DEFENSINS, SINCE THEY CAN DIRECTLY KILL PATHOGENS. THE GOAL OF THIS PROJECT IS TO UNDERSTAND THE ROLE OF ANTIMICROBIAL PEPTIDES IN TROUT SKIN IN NORMAL HEALTHY CONDITION AND DURING STRESS RESPONSES. OUR PRELIMINARY DATA SHOWS THAT TROUT BETA DEFENSINS ARE EXPRESSED IN THE SKIN AND THEIR EXPRESSION IS MODIFIED BY TRANSPORT STRESS. MOREOVER, WHEREAS ACUTE STRESS INCREASES THE NUMBERS OF SKIN-ASSOCIATED BACTERIA, CHRONIC STRESS SIGNIFICANTLY DECREASES SKIN-ASSOCIATED BACTERIAL NUMBERS. TROUT BETA DEFENSINS ARE POTENTIALLY CONTROLLED BY HEAT SHOCK AND STRESS RELATED FACTORS, SUGGESTING THAT THESE ANTIMICROBIAL MOLECULES CAN CONTRIBUTE TO CHANGE THE HEALTHY MICROBIOTA UNDER STRESS CONDITIONS. COMBINED, THESE PRELIMINARY DATA LED US TO HYPOTHESIZE THAT STRESS REGULATES DIFFERENT TROUT BETA DEFENSINS IN A MOLECULE-SPECIFIC MANNER RESULTING IN IMPAIRED RESPONSES TO PATHOGENS AND MICROBIOTA. GIVEN THE IMPACT THAT STRESS HAS ON THE SUSTAINABILITY OF THE FISH FARMING INDUSTRY, OUR RESULTS WILL EVALUATE ANTIMICROBIAL PEPTIDES AS THERAPEUTICS IN AQUACULTURE AND THEREFORE HAVE THE POTENTIAL TO INCREASE THE PRODUCTIVITY AND SUSTAINABILITY OF THE SALMONID FARMING INDUSTRY IN THE US.