Substitution of microalgae with microcapsule diet for two bivalve species, manila clam Ruditapes philippinarum and razor clam Sinonovacula constricta

In this study, a microcapsule diet was produced by spray-drying. Then, the filtration rate (FR) and ingestion rate (IR) of manila clam Ruditapes philippinarum were determined in relation to feeding on the microcapsule and microalgal Chaetoceros muelleri diets. Finally, two feeding experiments were conducted to evaluate the effects of increasing substitution of C. muelleri by the microcapsule on the survival rates, growth performances, biochemical compositions, and specific activities of digestive enzymes of two clams, R. philippinarum and razor clam Sinonovacula constricta. In experiment 1, the replacement of C. muelleri with the microcapsule was evaluated at three substitution levels (0%, 50%, and 100%) with R. philippinarum. In experiment 2, the replacement was evaluated at five substitution levels (0%, 25%, 50%, 75%, and 100%) with S. constricta. Results showed that the FR and IR of R. philippinarum in the microcapsule suspension were (4.07 +/- 0.19) mL clam(-1) min(-1) and (6.36 +/- 0.19) x 10(4) microcapsules clam(-1) min(-1), respectively. In experiment 1 and 2, no significant difference in survival rate of R. philippinarum or S. constricta was observed between different groups. The partial replacement of C. muelleri (25-50%) by the microcapsule diet did not significantly reduce the growth rates of these clams, while higher replacement (50-100%) did. The high-level microcapsule diet led to higher carbohydrate content when compared with high-level C. muelleri diet. In experiment 1, no significant difference in specific activity of amylase or lipase of R. philippinarum was observed between the 50% and 0% microcapsule groups. Meanwhile, no significant difference in specific activity of protease or lipase of S. constricta was observed between the 50% and 0% microcapsule groups in experiment 2. Our result suggested that the microcapsule was effective as a partial replacement of C. muelleri at up to 25-50% of dry weight of C. muelleri in clams.