Studies on triploid oysters in Australia: XII. Gonad discolouration and meat condition of diploid and triploid Sydney rock oysters ( Saccostrea commercialis) in five estuaries in New South Wales, Australia

The relative performance, in terms of meat condition, of triploid compared to diploid Sydney rock oysters varied among five widely distributed sites in New South Wales (NSW). Over the final year on leases, ploidy, month and the ploidy×month interaction had a significant effect on meat condition at all sites except for ploidy at the southern, Lake Pambula site. From March to December (autumn to the first month of summer), triploid condition indices were higher, or not significantly different from those of diploids at all sites. Condition indices of triploids were higher than those of diploids from May to November/December at four of the five sites. A higher condition index (CI) of triploids became apparent later in the sampling period for the Lake Pambula site in comparison to the remaining four sites. Triploid Sydney rock oysters were susceptible to brown discolouration of the gonad surface. Discolouration occurred in localised areas of the gonad and was not correlated to CI except for triploids at Lake Pambula. As discolouration was less noticeable during cooler months of the year, thus, coinciding with the generally superior condition of triploids relative to diploids during winter and spring, triploids remain a viable winter crop for farmers throughout NSW.