True electrotaxis and threshold voltages in the American crayfish Procambarus clarkii.

摘要

Experiments were conducted to obtain detailed information on the behavioural responses of American crayfish (Procambarus clarkii) to DC electric stimuli in the form of voltage gradients. Four different arrangements of electrodes producing different electric fields were tested in both indoor and outdoor tanks. The electrical intensity varied from 0.02-0.46 V/cm. We determined two threshold voltages: threshold voltage I, which induced parallel orientation of the animal to the electric field and forward crawling toward the anode (0.04-0.10 V/cm) and threshold voltage II, which induced flicking of the tail and backward swimming toward the anode (0.12-0.16 V/cm). The crayfish that displayed true electrotaxis moved to the anode when stimulated within the space enclosed by the electrodes. However, when the electrodes were elevated 5 or 10 cm off the bottom of the tank, the crayfish moved to the anode, crawled through the gap beyond it and out of the electric field. This movement beyond the anode cannot be explained by positive electrotaxis, but it can be interpreted as repulsion from the cathode. Anodal movement was most effective at 0.24-0.30 V/cm in the indoor tank and from 0.16-0.24 V/cm in the outdoor tank. The crayfish suffered electronarcosis when stimulated at 0.32-0.46 V/cm in the indoor tank and at 0.28-0.46 V/cm in the outdoor tank. They recovered from narcosis several minutes after the electric current was switched off. Thus, crayfish can be herded into a trap or net when stimulated by direct current of 0.24-0.30 V/cm, taking care not to induce electronarcosis.