Eighty percent of global fish production is consumed as food and currently over 50 percent of annual fish consumption worldwide is produced from aquaculture. Further, the United Nations Food and Agriculture Organization (FAO) forecasts that an additional 40 million tonnes (Mt) will be needed to feed the world population by 2030. Finfish aquaculture needs R&D in areas such as stock development, vaccine development, high performance diets and fish health, as well as genomic research in the areas of elite broodstock development, controlling environmental hazards and pest management strategies. On the west coast of Canada, farming of Atlantic salmon is still dominant, but Chinook salmon offers a native species alternative. Escapees mixing with wild stocks can be a potential hazard of this species, however. One mitigation strategy is to use triploid fish, as they are sterile. This strategy offers the added advantage that triploid fish do not mature sexually, a process that degrades market quality of the fillets. Chinook salmon maturation is a seasonal process, causing a rush to optimize the time of harvest before the fish mature. Non-maturing triploids will reduce losses due to early maturation of fish and extend the harvest time, providing increased profits. Triploid salmon are more susceptible to disease, however and that prevents the aquaculture industry from obtaining these benefits. The degree of this disease susceptibility differs between families of fish. This proposal examines the possibility that triploid fish have compromised immunity due to their genetic background causing family specific differences in expression of their immune genes combined with behavioural differences seen in triploids. It will also examine the possibility of ameliorating detrimental effects of triploidy through probiotic diets. The results of this research will provide information that allows the selection of broodstock and diet formulations that will produce triploid fish with minimal extra disease resistance, providing the environmental and economic benefits which triploid fish offer. Additionally, the results of this research will provide information on fish genetics and immunity so unique that it will provide benefits to the aquaculture of all finfish.