Abstract: Copepods use hydromechanical signals to detect prey and predators. However, little is known about their ability to differentiate prey from predators, neither from random water flow. We used laser- and video-optical equipment with a modified Schlieren optical pathway to observe a tethered copepod under variable hydrodynamic conditions. The results suggest that the copepod can distinguish between hydromechanical signals generated by an external source and those created by its own feeding current, even when these disturbances are within a similar speed range, as defined by measurements of spatial displacement of suspended particles. The data suggests that planktonic copepods may use a simple form of pattern recognition to distinguish between sources of signals: predators, prey, or random flow.