The relationship between body size and the field potentials generated by swimming crayfish

Aquatic animals generate electrical field potentials which may be monitored by predators or conspecifics. Many crustaceans use rapid, forceful contractions of the flexor and extensor muscles to curl and extend their abdomens during swimming in escape and locomotion. When crayfish swim they generate electrical field potentials that can be recorded by electrodes nearby in the water. In general, it is reasonable to assume that larger bodied crayfish will generate signals of greater amplitude because they have larger muscles. It is not known, however, how activity in particular muscles and nerves combines to produce the compound electrical waveform recorded during swimming. We therefore investigated the relationship between abdominal muscle, body size and the amplitude of nearby tailflip potentials in the freshwater crayfish (Cherax destructor). We found that amplitude was correlated positively with abdominal muscle mass. The mean amplitude recorded from the five smallest and five largest individuals differed by 440 microV, a difference sufficiently large to be of significance to predators and co-inhabitants in the wild.