Sviluppo di strumenti genomici applicati alla selezione di linee resistenti alla pasteurellosi nell'orata comune (Sparus aurata, L)

Fish pasteurellosis is an infectious disease that affects several fish species living in marine temperate waters. Its causative agent is the Gram - bacterium Photobacterium damselae subsp. piscicida (Phdp Vibrionaceae). Fish pasteurellosis represents a serious health problem for the majority of intensive sea bream hatcheries, with 90-100% mortality during disease outbreaks. Larvae and juveniles are the most susceptible stages. A potential strategy to prevent fish pasteurellosis is to select for disease-resistant animals. Aim of this work is to develop and optimise a set of genomic tools to analyse the genetics of disease resi stance and growth in the gilthead sea bream (Sparus aurata L.). To this end, genomic tools are first developed (repeat-enriched genomic libraries, linkage maps, marker sets for genetic analysis), then applied to the experimental population, which consisted of approximately 3000 animals, originating from uncontrolled crosses between several brodstock fish (mass spawning). The entire population was experimentally infected with a highly virulent strain of Phdp. Mortality was monitored for 20 days, every 12 hours. Upon completion of challenge experiment, genetic profiles at nine microsatellite loci were obtained for 1800 animals and for all (256) broodstock fish, for parentage assignment. A subset of families defined by means of genetic analysis was used to calculate heritability for growth and survival to infection. For growth, h2 ranged between 0.34 and 0.37. For disease resistance, h2 for survival at day 5 after infection was 0.4, while it decreased to 0.1 for day 10 after inferito. Using 90-100 microsatellite markers well spaced on the sea bream genome map, a whole-genome scan for growth and disease-resistance QTL was performed on five full/halfsib families (with n of individuals >70) for a total of 600 animals.