COMPARATIVE EFFECTS OF MICROALGAL SPECIES AND FOOD CONCENTRATION ON SUSPENSION-FEEDING AND ENERGY BUDGETS OF THE PEARL OYSTERS PINCTADA-MARGARITIFERA AND PINCTADA-MAXIMA (BIVALVIA, PTERIIDAE)

This study aimed to determine the influence of microalgal species and food concentration on Various physiological parameters and Scope for G rowth (SFG) in adults of 2 pearl oysters, Pinctada margaritifera and P . maxims. Clearance rate, pseudofaecal production rate, absorption eff iciency, respiration rate and excretion rate were determined over a ra nge of food concentrations using 2 microalgal diets. Tahitian Isochrys is sp. (T-Iso) and Dunaliella primolecta at 28 degrees C. Clearance, p seudofaecal production and respiration rates were significantly affect ed by microalgal diet. From these results, and because of the higher e nergy content of T-Iso, pearl oysters feeding on T-Iso had maximum val ues of SFG that were 1.5 to 2.1 times higher than when feeding on D. p rimolecta. Clearance rate and absorption efficiency were significantly related to food concentration as negative exponential relationships ( p < 0.001). Generally, pseudofaecal production, respiration and excret ion rates were significantly related to food concentration as positive linear relationships (p < 0.005). Optimal food concentrations for max imum SFG for P. margaritifera and P. maxima were 1 to 2 mg l(-1) and 2 to 3 mg l(-1), respectively. P, maxima was better adapted to a wider range of food concentrations. P. maxima maintained positive SFG up to 9 mg l(-1) food concentration when feeding on T-Iso and up to 3 mg l(- 1) when feeding on D. primolecta, while equivalent values for P. marga ritifera were 7 mg l(-1) and 5 mg l(-1), respectively. These results a re in accordance with P. maxima occurring in a wider range of habitats than P. margaritifera, and experiencing greater concentration ranges of suspended particulate matter.