Growth characteristics of Sydney rock oysters Saccostrea commercialis in relation to size and temperature

Sydney rock oyster Saccostrea commercialis spat obtained from a single spawning of four females and two males were allocated to six size classes six months after spawning. The spat from each size class were distributed among twelve treatments, which differed in length of time the spat spent in poor growing conditions, followed by good conditions, or conversely, in good growing conditions followed by poor conditions. A two-phase von Bertalanffy model and a regression model relating relative growth rate to size and water temperature gave similar fits to the results. The monthly growth rate of spat kept in good conditions depended on water temperature (reflected in the phases of the two-phase growth model) and size at the start of the month. It is concluded that because of the nature of oyster growth, comparison of growth rates of oysters of different sizes may be misleading.