The Sydney Rock Oyster (SRO) aquaculture industry is the largest and oldest aquaculture industry in NSW with annual revenue of approximately A$35 million (I&I NSW 2011). SRO breeding was initiated in 1990 through mass selection aiming to develop faster growing, winter mortality resistant lines (Nell et al. 2000). After five generations the average time to market size reduced by more than 12 months (Nell and Perkins 2005) and disease resistant lines were available. In 2004, the first progeny from 5th generation fast growing lines were distributed to oyster farmers in NSW. In comparison to wild-caught oysters, these stocks demonstrated clear differences in reproductive behaviour, which affected marketability in various estuaries throughout NSW (O’Connor and Dove 2011). While industry demand for selectively bred SRO remains strong (2011/2012 spat sales will exceed 20,000,000 and will form the basis of more than 20% of total production), these changes pose both challenges and opportunities for the entire SRO production cycle from the hatchery, where oysters in “ripe” reproductive condition are required for spawning, through to market where reproductive condition is a major determinant in “saleability”.

With the progression of the SRO breeding program from 3 “base” mass selected lines to 120 pair-mated families, investigation into the biology behind the altered condition index of selectively bred oysters is of great importance. Initially, there is a fundamental need for reproductive concurrency among lines to allow breeding. Secondly, genetic variability in reproductive condition offers the opportunity to manage marketability through the selection of lines whose characteristics suit market requirements.