The tropical pearl oysters Pinctada margaritifera (Linnaeus) and P maxima Janieson are=520 \\ suspension feeders of malor economic importance. P margaritifera occurs in coral reef waters characterised=520 \\ by oligotrophy and low turbidity. P. maxima habitats are generally characterised by high terrigenous=520 \\ sediment and nutrient inputs, and productivity levels. These differences in habitat suggest=520 \\ that P. margaritifera will feed more successfully at low food concentrations, while P. maxima will cope=520 \\ with a wider range of food concentrations and more silty conditions. The effect of varying concentrations=520 \\ of natural suspended particulate matter (SPM) on clearance rate (CR), pseudofaeces production,=520 \\ absorption efficiency (abs.eff.),r espired energy (RE) and excreted energy (EEJ was determined for P.=520 \\ margantifera and P maxlma. The resultant scope for growth (SFG) was deterrmned and related to=520 \\ habitat differences between the oysters. There was no selective feeding on organic particles in either=520 \\ species. P. rnargaritifera had higher CR at low SPM concentration (<2 mg I-'), while P. maxima had=520 \\ higher CR under turbid conditions (SPM: 13-45 mg 1-'). The latter species produced less pseudofaeces=520 \\ in relation to its filtration rates; consequently, this species ingested more SPM than P. margaritifera. P.=520 \\ maxima had positive SFG over a wider range of SPM concentrations (up to 30-40 mg I-') while P. margaritifera=520 \\ maximised SFG under low SPM conditions (<3 mg I-'). Thus feeding responses and energy=520 \\ balance reflected the typical habitats of each species. P, margaritdera retained smaller particles than P.=520 \\ maxima, enabling it to consume a wider particle size range of SPM at low food levels. P. maxima was=520 \\ adapted to its environments of greater SPM load through greater ingestion rates and higher digestive=520 \\ ability. The optimum SPM concentrations and particle size range for P. margaritifera (SPM < 5 mg I-',=520 \\ size > 3 pm) and P. maxima (SPM = ca 3 to 15 mg I-', size > 4 pm) may be used for selection of optimum=520 \\ pearl culture sites.