In this study changes in the locomotory behaviour of three different crustacean species (D. magna Straus, D. pulex Leydig, H. inermis Leach) have been used for studying sublethal effects of the heavy metals copper (Cu) and cadmium (Cd). The behavioural responses were determined by a real time image analysis, using a video camera and a Pentium-PC equipped with a standard low cost frame grabber. For a sequence of 50 images per group, where 10 test organisms were moving simultaneously, the trajectories have been reconstructed in binary image sequences. As biological end points we defined the...