HYDRODYNAMIC ORIENTATION OF CRAYFISH (PROCAMBARUS-CLARKII) TO SWIMMING FISH PREY

Reversibly blindfolded crayfish (Procambarus clarkii) react to small s wimming fish (Astyanax fasciatus mexicanus) approaching or passing nea rby with antennal and cheliped movements and body turns (Fig. 3). We s tudied the accuracy and dynamics of crayfish orientation responses to the previously analyzed hydrodynamic disturbances caused by the fish, mostly produced by tail flicks. Antennal and cheliped movements starte d slightly before the onset of turning responses (Fig. 4). Antennal sw eeps were performed most rapidly. 50% of the appendage sweeps resulted in contacts with the fish (Fig. 5). Most turns were directed toward t he stimulus (Fig. 6). Response amplitudes increased with increasing st imulus angle. Turns were accurate for small stimulus angles, but small er than expected for larger ones. Sweeps of ipsilateral antennae and c helipeds were generally directed backwards, while those of contralater al appendages were smaller and directed forwards. The amplitudes of ap pendage sweeps first increased with increasing stimulus angle and then decreased again for more caudal stimulus directions. Lateral stimuli (60 degrees-120 degrees) from opposite sides were usually significantl y distinguished. The amplitudes of the different elements of orientati on behaviour were highly correlated with each other, indicating that t hey were directed by the same sensory input.