In this study, the subacute toxicity of the heavy metal cadmium to Hippolyte inermis Leach was investigated. Subacute effects were evaluated using changes in the locomotory behavior (i.e., moving velocity and moving distance) as indicators. The locomotory activity was analyzed by means of real-time image analysis, using a video camera and a Pentium PC equipped with a standard low-cost frame grabber. For a sequence of 3000 images per treatment, where 10 shrimp were moving simultaneously, the trajectories were reconstructed as binary image sequences. The locomotory activity of the test organisms was analyzed under normal conditions (without heavy metal stress) and after application of a subacute Cd stress. Test animals were stressed by Cd of the following 3 concentrations: 1 (C1), 2 (C2), and 3.5 ppm (C3). Shrimp were exposed to the heavy metal concentrations for 12 h under static conditions. At initiation (0 h) of Cd exposure, the test animals showed a significant (p ≤ 0.05) decrease in the average swimming velocity at C3. After 3 h of Cd exposure, the median moving velocity was for the first time highly significantly (p ≤ 0.01) reduced with the 1 ppm Cd treatment.