| Summary: | This report is an investigation into the 2020 generation of triploid salmon in Northern Norway and their diploid comparators. The trajectory of 16 fish groups comprising more than 10 million fish is described throughout their production cycles. The commercially cultivated fish vary in origin and rearing environment, and experience different disease and treatment events. The acquired dataset provides a uniquely whole description of the aquaculture production cycle but is challenged by the many confounding factors. Rather than make isolated analyses we evaluated the motivations of farmers within the complex system of management regimes, commercial structures, and animal health. We find that farmers and fish health personnel make decisions which balance welfare needs with production goals, but their decisions are constrained and often forced by regulations. Furthermore, a repeated pattern has emerged in which farmers choose to apply riskier handing operations on fish which are perceived to be stronger while reserving gentler operations for those that are perceived to be weaker, which more often are triploid fish. This was also shown in that they typically chose to fast the triploid fish longer than the diploid before delousing operations. The movement of fish between farms and applying delousing treatments increases mortality in the weeks after the operation compared to before, regardless of ploidy. Mortality especially increased after thermal and mechanical treatments even though these were preferentially applied to fish perceived to be stronger. The susceptibility of triploid fish to health problems was demonstrated by higher prevalence of winter ulcers and mortality during the winter for triploid compared to diploids, especially when the fish were transferred to sea that Autumn. Overall, the triploids were also inferior in their economic prospect for the farmer, compared to diploids they had lower product quality at harvest, required more feed per kg produced, and had a higher cumulative mortality by the time of ...
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