Despite the ecological and economic importance of vertebrate suspension feeders, hypotheses about particle entrapment mechanisms inside their oral cavities have rarely been tested and the fluid mechanics of filtration by vertebrates has not been modelled. This project will develop a mathematical model of flow fields around and particle retention by the gill raker of blackfish (Cyprinidae), and will apply this model to Pacific herring (Clupeidae) and northern anchovy (Engraulidae). Using a fiberoptic endoscope and thermistor flow probe to record the first images and water velocities inside the oral cavity of a vertebrate suspension feeder, an unexpected filtration mechanism was documented in blackfish. Gill rakers, assumed to be the site of particle retention in fishes, act in blackfish as barriers that direct particle-laden water to the mucus-covered oral roof. A thermistor flow probe will provide empirical values for the model parameters in herring and anchovy, and a fiberoptic endoscope will establish whether the model accurately predicts the pattern of flow at the rakers. The model will indicate the flow velocities and raker morphologies that are associated with the functioning of rakers as barriers versus filters, and will be applicable to a diversity of fish species and other suspension feeders.
