** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** FOR THE PAST SEVERAL DECADES, AQUACULTURE HAS BEEN THE FASTEST GROWING SECTOR OF ANIMAL AGRICULTURE, WITH WORLDWIDE PRODUCTION OF FISH AND SHELLFISH TRIPLING IN VOLUME PRODUCED SINCE 1995. CURRENTLY, AQUACULTURE AND FISHERIES EACH CONTRIBUTE APPROXIMATELY HALF TO THE DEMAND FOR AQUATIC PROTEIN. A RECENT ESTIMATE INDICATES THAT AQUACULTURE PRODUCTION MUST INCREASE BY AN ESTIMATED 157% TO MEET THE PROTEIN DEMAND OF AN EVER-GROWING GLOBAL POPULATION AND AVOID INCREASED RELIANCE UPON CAPTURE FISHERIES. BOTH EXPANDING AQUACULTURE PRODUCTION CAPACITY AND IMPROVING PRODUCTION EFFICIENCY ARE ESSENTIAL TO MEET THE FUTURE DEMAND FOR AQUACULTURE-DERIVED AQUATIC PROTEIN. SELECTIVE BREEDING HAS BEEN APPLIED IN AQUACULTURE AS A STRATEGY TO INCREASED PRODUCTION EFFICIENCY. FISH BREEDERS HAVE PRIMARILY FOCUSED ON INCREASING GROWTH, FILLET YIELD, AND DISEASE RESISTANCE SINCE THESE TRAITS HAVE HIGH HERITABILITY AND DIRECTLY BENEFIT PRODUCTION EFFICIENCY AND ANIMAL WELFARE. HOWEVER, IT IS RECOGNIZED THAT BREEDING FOR TRAIT IMPROVEMENT CAN HAVE UNINTENDED NEGATIVE CONSEQUENCES ON OTHER PRODUCTION TRAITS, SUCH AS TOLERANCE TO LOW DISSOLVED OXYGEN (HYPOXIA). SALMONID FISH SPECIES, SUCH AS RAINBOW TROUT, REQUIRE HIGH CONCENTRATIONS OF DISSOLVED OXYGEN FOR OPTIMAL GROWTH. HOWEVER, ADDING SUPPLEMENTAL OXYGEN INTO RACEWAYS OF LARGE RAINBOW TROUT OPERATIONS IS NOT ECONOMICALLY FEASIBLE SO FARMERS USE ALTERNATIVE STRATEGIES SUCH AS REDUCING FISH DENSITY AND INCREASING WATER FLOW TO KEEP DISSOLVED OXYGEN WITHIN ACCEPTABLE LIMITS; UNFORTUNATELY, THESE STRATEGIES ALSO REDUCE PRODUCTION CAPACITY. THIS PROJECT ADDRESSES THIS BY CHARACTERIZING GENETIC VARIATION IN HYPOXIA TOLERANCE AMONG LINES OF RAINBOW TROUT WITH IMPROVED PRODUCTION TRAITS AND INVESTIGATING NUTRITIONAL STRATEGIES THAT INCREASE HYPOXIA TOLERANCE.THE FIRST OBJECTIVE OF THIS PROJECT IS TO CHARACTERIZE HOW GENETICALLY IMPROVED LINES OF RAINBOW TROUT WITH HIGH FILLET YIELD ANDIMPROVED DISEASE RESISTANCE RESPOND TO HYPOXIA STRESS. ALTHOUGH THESE SELECT LINES ARE VALUED BY PRODUCERS BECAUSE OF THEIR HIGH PRODUCT YIELD AND IMPROVED HEALTH, IT IS UNKNOWN WHETHER THEIR HYPOXIA TOLERANCE DIFFERS FROM STANDARD LINES. FOR THIS STUDY, STANDARD AND GENETICALLY IMPROVED LINES OF RAINBOW TROUT WILL BE EXPOSED TO GROW-OUT CONDITIONS CHARACTERIZED BY CHRONIC HYPOXIA. GROWTH PERFORMANCE WILL BE ANALYZED FOR HOW WELL FISH PERFORM UNDER THESE CONDITIONS; GLOBAL GENE EXPRESSION WILL ALSO BE EVALUATED TO IDENTIFY GENETIC AND PHYSIOLOGICAL MECHANISMS CONTRIBUTING TO PERFORMANCE DIFFERENCES. FINDINGS FROM THIS STUDY WILL INDICATE IF SELECTION FOR INCREASED FILLET YIELD OR DISEASE RESISTANCE HAS A NEGATIVE CONSEQUENCE ON HYPOXIA TOLERANCE AND DETERMINE WHETHER LINE-SPECIFIC HUSBANDRY STRATEGIES ARE BENEFICIAL WHEN THESE GENETICALLY IMPROVED LINES ARE USED FOR PRODUCTION.A SECOND OBJECTIVE FOCUSES ON THE POTENTIAL FOR DIETARY CHOLINE TO ALLEVIATE NEGATIVE EFFECTS OF HYPOXIA STRESS ON REPRODUCTIVE PERFORMANCE IN RAINBOW TROUT. IN THIS STUD,Y, FEMALE RAINBOW TROUT WILL CONSUME CHOLINE-SUPPLEMENTED DIETS AND BE EXPOSED TO CHRONIC HYPOXIA AS THEY PROGRESS THROUGH SEXUAL MATURATION. INDICES OF REPRODUCTIVE PERFORMANCE SUCH AS EGG SIZE, EGG YIELD, AND HATCH RATE WILL BE EVALUATED TO DETERMINE WHETHER EXCESS DIETARY CHOLINE PROVIDED BROODSTOCK WITH A PERFORMANCE ADVANTAGE. IN ADDITION, GROWTH AND HYPOXIA TOLERANCE OF OFFSPRING WILL BE EVALUATED TO DETERMINE IF MATERNAL TREATMENTS HAVE TRANSGENERATIONAL EFFECTS. THESE FINDINGS CAN IDENTIFY A NUTRITIONAL APPROACH TO IMPROVING REPRODUCTIVE SUCCESS WHEN BROODSTOCK ARE EXPOSED TO HYPOXIA STRESS. ADDITIONALLY, IDENTIFICATION OF TRANSGENERATIONAL EFFECTS IN OFFSPRING MAY INTRODUCE BROODSTOCK CONDITIONING AS A HUSBANDRY STRATEGY FOR IMPROVING HYPOXIA TOLERANCE.TOGETHER, THESE TWO OBJECTIVES WILL IMPROVE OUR UNDERSTANDING OF GENETIC SELECTION EFFECTS ON NON-SELECTEDPHENOTYPES AND MATERNAL EFFECTS ON OFFSPRING PERFORMANCE. THIS INFORMATION WILL AID IN STAKEHOLDER'S UNDERSTANDING OF A FEW BASIC HUSBANDRYTECHNIQUES THAT CAN BE ALTERED SLIGHTLY TO AFFECT PERFORMANCE.