11. ELECTRORECEPTION
495
of their electric organs.” These fish proved to be extremely sensitive to
applied fields as well as to distortions in the fields they themselves
generated ( Lissmann, 1958; Lissmann and Machin, 1958). Subsequently,
it has become apparent that some catfish and most elasmobranchs
possess electroreceptors but lack electric organs ( Dijkgraaf, 196$;
Dijkgraaf and Kalmijn, 1963, 1966; Lissmann and Machin, 1963; Murray,
1967; Roth, 1968, 1969). In these instances, it is likely that the fish primarily detect signals of external origin, although the receptors may also
be responsive to fields set up by the fish‘s own muscles. Other groups of
fish may yet be shown to have electrosensory systems, and there are
morphological suggestions of electroreceptors in several groups
(Dijkgraaf, 1963).
All the known electroreceptors are modified lateral line organs (see
Chapter 8 by Flock, this volume). In the weakly electric freshwater fish,
they are distributed along most or all of the body length as would be
expected in a sensory system that detects distortions in a field set up by
the fish itself. As in their mechanoreceptive precursors, the initial active
transformation of the stimulus is carried out by receptor cells that are
presynaptic to the innervating afferent fiber.
One may classify the electrosensory systems as passive, if they detect
signals of external origin, and active, if they are equipped with their own
energy source, that is, an electric organ (Bennett, 1967; Machin, 1962).
Familiar examples of active sensory systems are echo locating systems of
bats, cetaceans, and oil birds (Griffin, 1958), and one is justified in using
the term “electrolocation.” It should be emphasized that electrolocation
does not involve electromagnetic waves; the system instead operates
analogously to an ohmmeter or impedance measuring device. Of course,
receptors in an active sensory system can also operate passively. Furthermore, freshwater weakly electric fish have two or three kinds of electroreceptor. One kind of receptor is insensitive to the high frequencies
usually predominant in the organ discharge and operates passively while
the remaining receptors operate actively. In the skates, which are marine
weakly electric fish, the organ discharge is infrequent and the receptors
probably function passively most of the time. The same consideration
appears to apply to the weakly electric organ of the torpedinid Narcine.
Many electric fish can detect each other’s discharges, and there is
evidence that weakly electric organs can function in intraspecific com’ Chapter 10 of this volume should be consulted for verification or elaboration
of statements made in the present chapter about physiology and discharge patterns
of these organs. A briefer review of electric organs and electroreception is given
-
by Bennett (1970), and a short summary of most recent data appears in Bennett
(1971b).
495
of their electric organs.” These fish proved to be extremely sensitive to
applied fields as well as to distortions in the fields they themselves
generated ( Lissmann, 1958; Lissmann and Machin, 1958). Subsequently,
it has become apparent that some catfish and most elasmobranchs
possess electroreceptors but lack electric organs ( Dijkgraaf, 196$;
Dijkgraaf and Kalmijn, 1963, 1966; Lissmann and Machin, 1963; Murray,
1967; Roth, 1968, 1969). In these instances, it is likely that the fish primarily detect signals of external origin, although the receptors may also
be responsive to fields set up by the fish‘s own muscles. Other groups of
fish may yet be shown to have electrosensory systems, and there are
morphological suggestions of electroreceptors in several groups
(Dijkgraaf, 1963).
All the known electroreceptors are modified lateral line organs (see
Chapter 8 by Flock, this volume). In the weakly electric freshwater fish,
they are distributed along most or all of the body length as would be
expected in a sensory system that detects distortions in a field set up by
the fish itself. As in their mechanoreceptive precursors, the initial active
transformation of the stimulus is carried out by receptor cells that are
presynaptic to the innervating afferent fiber.
One may classify the electrosensory systems as passive, if they detect
signals of external origin, and active, if they are equipped with their own
energy source, that is, an electric organ (Bennett, 1967; Machin, 1962).
Familiar examples of active sensory systems are echo locating systems of
bats, cetaceans, and oil birds (Griffin, 1958), and one is justified in using
the term “electrolocation.” It should be emphasized that electrolocation
does not involve electromagnetic waves; the system instead operates
analogously to an ohmmeter or impedance measuring device. Of course,
receptors in an active sensory system can also operate passively. Furthermore, freshwater weakly electric fish have two or three kinds of electroreceptor. One kind of receptor is insensitive to the high frequencies
usually predominant in the organ discharge and operates passively while
the remaining receptors operate actively. In the skates, which are marine
weakly electric fish, the organ discharge is infrequent and the receptors
probably function passively most of the time. The same consideration
appears to apply to the weakly electric organ of the torpedinid Narcine.
Many electric fish can detect each other’s discharges, and there is
evidence that weakly electric organs can function in intraspecific com’ Chapter 10 of this volume should be consulted for verification or elaboration
of statements made in the present chapter about physiology and discharge patterns
of these organs. A briefer review of electric organs and electroreception is given
-
by Bennett (1970), and a short summary of most recent data appears in Bennett
(1971b).