The fitness of two bivalves Saccostrea glomerata and Ostrea angasi exposed to a metal contamination gradient in Lake Macquarie, NSW Australia was assessed by measuring subcellular biomarkers (total antioxidant capacity, lipid peroxidation and lysosomal stability), energy metabolism responses and embryo development. Oyster tissue metal concentrations (Cu, Zn, Se, Cd and Pb) in both oyster species significantly increased over 31 days along the metal contamination gradient, but not in proportion to sediment metal concentrations. O. angasi had slightly higher metal concentrations but overall metal concentrations of both species were similar. In response to exposure to metal contaminated sediments, both oyster species showed a decrease in total antioxidant capacity, an increase in lipid peroxidation and decreased lysosomal membrane stability. Cellular Energy Allocation and energy consumption decreased with a corresponding usage of protein, lipid and glycogen stores at most sites. S. glomerata also demonstrated a significant reduction in embryo development. These responses demonstrated that exposure to metal-contaminated sediments impaired the fitness of S. glomerata and O. angasi in Lake Macquarie, NSW, Australia. To integrate and interpret the range of biomarkers measured in future studies, the effect of behavioural responses of bivalve mollusc to metal stress, bivalve closure and subsequent anaerobic metabolism should be evaluated to fully understand these responses.