An Electric Sense in Crayfish?
The Biological Bulletin
A variety of aquatic vertebrates, including teleost and non-teleost fish, amphibians, and monotreme mammals, are sensitive to low-frequency electric signals with thresholds of low nanovolts per centimeter to high microvolts per centimeter, have specialized detectors for these signals, and use electroreception to locate food or orient in their environment (1-9). Although invertebrates would similarly benefit from an electric sense (10), none are known to use it. A recent report concluded that
... t concluded that the freshwater crayfish species Cherax destructor responds to electric fields (11). Some years ago, we investigated whether another species of freshwater crayfish, Procambarus clarkii, has an electric sense and uses it to find prey. Weak fields were produced across water-bridge electrodes spaced 1-5 cm apart, and exploratory feeding behaviors such as touching, grabbing, and tugging at the electrodes using the claws, legs, and mouthparts were examined. Our results show that P. clarkii responds to fields with intensities of 20 mV/cm and greater. We also recorded from sensory neurons in P. clarkii legs and claws and found that the only field-sensitive cells had similarly high thresholds and were also responsive to chemical and mechanical stimuli. We conclude that P. clarkii does not have a high-sensitivity, specialized electric sense used in locating food. Male and female freshwater crayfish (Procambarus clarkii), 55-80 mm total length, were shipped from Atchafalaya Biological Supply Co. (Louisiana), kept in our laboratory, and fed shrimp pellets. A week before behavioral assays, animals were isolated without food in holding aquaria under a photoperiod of 12 h light to 12 h dark. We assumed that if P. clarkii has an electric sense, these crayfish would use