FISH FARMING PROVIDES ALL US CONSUMERS WITH A HIGH-QUALITY FOOD SOURCE. INTENSIVE FISH FARMING, HOWEVER, CAN RESULT IN DISEASE OUTBREAKS. MOST OF THE DISEASES AFFECTING FARMED FISH START AT MUCOSAL BARRIERS SUCH AS THE SKIN, GILLS, GUT AND OLFACTORY ORGAN. THUS, THERE IS A NEED FOR EFFECTIVE MUCOSAL VACCINES FOR USE IN AQUACULTURE. NASAL VACCINATION IS HIGHLY EFFICACIOUS AND PROTECTS SALMONIDS FROM VIRAL AND BACTERIAL PATHOGENS. WE HYPOTHESIZE THAT NOT ONLY THE OLFACTORY MUCOSA, BUT ALSO IMMUNE STRUCTURES RECENTLY IDENTIFIED IN OTHER AREAS OF THE TROUT NASAL CAVITY, ARE INVOLVED IN THE IMMUNE RESPONSE DURING VACCINATION. THE GOAL OF THIS PROPOSAL IS TO CHARACTERIZE THE UNIQUE ASPECTS OF THESE PREVIOUSLY IGNORED STRUCTURES OF THE RAINBOW TROUT NASAL CAVITY. TO THAT END, WE WILL EVALUATE THE INNATE AND ADAPTIVE IMMUNE RESPONSES IN RAINBOW TROUT DURING THE COURSE OF VACCINATION USING VIRAL AND BACTERIAL VACCINES DELIVERED INTRANASALLY OR BY INJECTION. WE PREDICT THAT THESE STRUCTURES PLAY COMPLEMENTARY IMMUNOLOGICAL FUNCTIONS TO THOSE IN THE OLFACTORY MUCOSAL EPITHELIUM. THESE FINDINGS WILL INCREASE OUR UNDERSTANDING OF HOW FISH DEFEND THEMSELVES FROM MUCOSAL INFECTIONS AND WILL PROVIDE A PLATFORM TO DESIGN BETTER MUCOSAL VACCINES FOR FARMED SALMONIDS. THESE IMPROVED VACCINES WILL INCREASE THE SUSTAINABILITY AND PRODUCTION OF THE FISH FARMING INDUSTRY IN THE US.