Fluid Dynamics of Chemical Scent Detection in Stingrays*

Stingrays are macrosmatic, relying on their sense of smell as one of their primary senses for survival. Olfaction is crucial for predator and prey recognition, navigation and tracking, and reproductive signaling. While these fishes rely on water flow to direct odors into their nose, there have been very few studies on the fluid dynamics of their olfaction. With an odor-impeding boundary layer and no direct pump-like system, how do these fishes efficiently capture chemical stimuli? To understand how nasal morphology influences chemical detection, models of the 4 nasal morphotypes seen in batoids were 3D printed in clear resin from CT scans. Models were mounted in a water tunnel and dye visualization and particle image velocimetry methods were performed at various Reynolds numbers. Models were printed with their mouths opened and tubing connecting to a syringe pump to mimic respiration. To determine how respiration indirectly influences nasal irrigation, models were tested with a continuous “inhale” respiratory rate. The pitch of the head was investigated at 0 and 8°, to mimic the change in body orientation with increased swimming speed. Particle image velocimetry was used to measure the flow. We found that different nasal geometries produce different patterns of flow and odor capture mechanisms. Pitch and respiratory processes are also crucial parameters for odor detection. This study lends insights into the fluid dynamics of chemical sensing in the marine environment and highlights the importance of the morphology of the system for odor capture and circulation.