In 1990, NSW Fisheries initiated a mass selection programme in Port Stephen
s, NSW, with the aim of breeding faster growing Sydney rock oysters Saccost
rea glomerata (Gould 1850). After two generations of selection, an average
weight for age advantage of 18% (range 14-23% per breeding line) was achiev
ed. This equates to a reduction of 3 months in the time taken to reach mark
et size. Experiments are planned to determine how much of this 3 months adv
antage is additive to the 6 months advantage this laboratory has already ob
tained using triploid S. glomerata. A parallel set of S. glomerata breeding
lines was established on the Georges River, NSW, to include selection for
resistance to the protistan parasite Mikrocytos roughleyi, the causal agent
of winter mortality. The programme was disrupted by the outbreak of QX dis
ease Marteilia sydneyi, another protistan parasite, in 1994. In 1997, the b
reeding programme was reorganized and expanded. New lines were bred from oy
sters that had survived both QX and winter mortality. After one generation,
a small improvement in resistance to QX has been recorded; however, the ex
posure of further generations to M. sydneyi will be required to confirm an
increase in resistance.