Economic weights for disease resistance in Sydney rock oysters

Sydney rock oyster farmers and wholesalers surveyed in 2006 provided production and economic data, which were used to construct a profit function for the industry. Economic values, assuming a range of initial mortality levels, were estimated using the partial first derivative of the profit function. Economic values were differentiated for Winter Mortality (WM) and QX disease taking into account the growth phase at which mortality occurred and reported mortality levels for these diseases. Increased mortality leads to higher costs associated with replacing dead oysters, which is done by attaining additional spat (young oysters). Plus there are additional grading costs, particularly at the later stages of growth, which increased the economic value for mortality occurring in later growth phases. There was little difference in the corresponding economic values between nursery and initial grow out growth phases, but mortality during the final grow out growth phase had large economic values. For QX disease, the high level of mortality typically occurring in the final growth phase (90%) resulted in an economic value of -$0.146/% per dozen oysters. No successful management practices are available to manage QX disease. Winter Mortality commonly causes approximately 46% mortality, resulting in an economic value of -$0.061/%. When management strategies were used to reduce initial mortality levels (between 10% and 30%), economic values were between -$0.047/% and -$0.052/% respectively. The difference between the economic values for WM and QX disease resistance show that selecting against mortality from QX disease is more economically important to a breeding program than selecting against WM, assuming similar genetic variation for both diseases.