Mortality in single-pair mating families of QX disease-resistant and wild-type Sydney rock oysters (Saccostrea glomerata)

QX disease causes mass mortalities among Sydney rock oysters (Saccostrea glomerata).To overcome commercial production losses, Industry & Investment NSW has been developing mass selected QX diseaseresistant breeding lines since1997.This breeding programme has signi¢cantly reduced QX-associated mortality in the Lime Kiln Bar (LKB) breeding line relative to non-selected, wild-type (WT) oysters.The current study assessed mortality in families produced by single-pair mating between LKB and WT oysters.When these families were grown in a QX disease-prone area, the progeny of LKB Â LKB crosses had signi¢cantly lower mortality compared with LKB Â WT or WT Â WT families.Mortality in the di¡erent crosses was associated with infection by sporulating Marteilia sydneyi, the parasite responsible for QX disease.Overall, the study identi¢ed a strong association between parentage and mortality resulting from QX disease.