A new tool was recently developed using two colors of 2 µm fluorescent beads to measure ingestion rates, gut volume, and gut passage time in bivalve larvae, specifically Crassostrea gigas (Pacific oysters). In this study, several assumptions were tested that formed the basis of the method: larvae do not select for beads based on color, that the two colors of beads can be added at a ratio constant across all vials, and that the larvae treat the beads similar to algae cells, their natural food source. It was found that some of the assumptions were not met; however, when assumptions are not met, modifications can be made during data analysis so that the method may still be used as a tool to compare the feeding physiology and behavior of bivalve larvae during experiments.