Behavioural response of the cladoceran Daphnia magna STRAUS to sublethal Copper stress--validation by image analysis

In this study changes in the locomotory behaviour of the freshwater cladoceran Daphnia magna STRAUS were used as sublethal indicators of toxic copper (Cu) stress. 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 daphnids were moving simultaneously, the trajectories have been reconstructed in binary image sequences. As biological endpoints, we defined the average swimming velocity and the average duration of swimming activity and inactivity. The behavioural responses of the daphnids were analysed under normal conditions (without Cu stress) and after application of sublethal Cu stress of following concentrations (in microg l(-1) (ppb)): C1=1, C2=5, C3=10, C4=20, C5=30. The test organisms were exposed to the Cu concentration for 24 h under static conditions. Already after 9 h of Cu-exposure a significant (*P<0.05) decrease of the average swimming velocity could be observed at the group of the highest Cu concentration (30 ppb). After 13 h of Cu-contamination the swimming velocity was significantly (*P<0.05) reduced at group of 20 ppb Cu-treatment and after 14 h a significant (*P<0.05) decrease of the average swimming velocity could be measured at the group of 10 ppb Cu-treatment. No significant decrease of the swimming velocity could be observed in the 1 and 5 ppb Cu-treatment.