Optimization of intensive rearing systems, especially those involved in yields of marketable sizes of bivalve molluscs, must pass through several technical improvements. One such improvement is described here: it concerns the experimental use of a simple centrifugal pump that causes artificial breakage of the chains of the diatom Skeletonema costaturn (Grev. ) Cleve used to feed adults of the Manila clam Ruditapes philippinarum (Adams and Reeve). The breakage process progressively reduced the size distribution of the algal particles but eliminated all algal chains longer than 60 pm. Scanning electron microscope (SEM) observations indicated that the breakage process impacts on both algal cells themselves (60% of broken structures) and siliceous structures connecting sibling cells (40% of broken structures). Some expected implications of the breakage process are presented in connection with the intensive rearing system and nutritional requirements of Manila clam.