No. 43: Jan-Feb 1986
Mammals such as bats and porpoises have their acoustical navigational gear, while many fish have opted for electrical methods of scanning their surroundings. The short-range "radars" of these fish are marvelously sophisticated, considering the low limb fish occupy on the Tree of Life. In fact, the following introductory paragraph from an article in Nature sounds almost as if it came from a textbook on electronic signal processing.
"Behavioural experiments have demonstrated that certain species of fish can perform remarkable analyses of the temporal structure of electrical signals. These animals produce an electrical signal within a species-specific frequency range via an electric organ, and they detect these signals by electroreceptors located throughout the body surface. In the context of one electrosensory behaviour, the jamming avoidance response (JAR), the fish Eigenmannia determines whether a neighbour's electric organ discharge (EOD), which is jamming its own signal, is higher or lower in frequency than its own. The fish then decreases or increases its frequency, respectively. To determine the sign of the frequency difference, the fish must detect the modulations in the amplitude and in the differential timing, or temporal disparity, of signals received by different regions of its body surface. The fish is able to shift its discharge frequency in the appropriate direction in at least 90% of all trials for temporal disparities as small as 400 ns."
(Rose, Gary, and Heiligenberg, Walter; "Temporal Hyperacuity in the Electric Sense of Fish," Nature, 318:178, 1985.)
Comment. ns = nanosecond = 10-9 second. There must be some chips in those fish! Sorry, couldn't resist that one.