11. ELECTRORECEPTION
559
Table I1
Behavioral and Receptor Thresholds"
Computed Measured
Threshold receptor receptor
Behavioral
gradient stimulus threshold
Fish
response
(rV/cm)
(PV)
(PV)
Skates, dogfish, sharks Heart rate acceleration
0.01
0.2
2
Gymnarchus
Feeding
0.15
4
1006
Mormyrids
Change in organ dis50
500
20w
charge rate
Catfish
Clarias
Feeding
1
10
K ryptopterus
100
Gymnotids
Jamming avoidance
3-100
15-500
100
References in text.
Mormyrid tonic receptors.
Large receptors.
pV/cm, and the minimum receptor threshold is about 2 pV (Dijkgraaf
and Kalmijn, 1966; Murray, 1967). Since the longest ampullary canals
were probably 20 cm or more in length in the behavioral experiments, an
applied field of 0.01 pV/cm would result in a stimulus to these receptors
of 0.2 pV or more.
The Gymnurchus studied by Machin and Lissmann (1960 ) was
sensitive to fields of about 0.15 pV/cm, and a slightly higher threshold
was calculated for distortions of fields produced by objects. Since the
animal was about 50 cm in length, the field strength would result in a
receptor stimulus of about 4 pV. The thresholds of receptors in Gymnurchus have not been well studied, but the required sensitivity is only
10-20 times greater than is observed in small (tonic) receptors in mormyrids. In Gymnarchus the threshold for high frequency rectangular
pulses is given by the dc component of the stimuli. This observation
indicates that the phasic receptors are no more sensitive to the ac component of this form of stimulus than the tonic receptors are to the dc
component ( granted that these classes of receptor exist).
The catfish Clarias has been shown to be sensitive to a gradient of
about 1 pV/cm in training using food reinforcement (Lissmann and
Machin, 1963). For a 20-cm animal this would correspond to a receptor
stimulus of about 10 pV assuming that the skin is of high resistance.
Receptor thresholds 5-10 times this value have been observed in the
transparent catfish Kryptopterus ( Bennett, 1971a,b).
In mormyrids, threshold gradients along the entire fish for electric
pulses to evoke changes in organ discharge frequency are about 0.05
559
Table I1
Behavioral and Receptor Thresholds"
Computed Measured
Threshold receptor receptor
Behavioral
gradient stimulus threshold
Fish
response
(rV/cm)
(PV)
(PV)
Skates, dogfish, sharks Heart rate acceleration
0.01
0.2
2
Gymnarchus
Feeding
0.15
4
1006
Mormyrids
Change in organ dis50
500
20w
charge rate
Catfish
Clarias
Feeding
1
10
K ryptopterus
100
Gymnotids
Jamming avoidance
3-100
15-500
100
References in text.
Mormyrid tonic receptors.
Large receptors.
pV/cm, and the minimum receptor threshold is about 2 pV (Dijkgraaf
and Kalmijn, 1966; Murray, 1967). Since the longest ampullary canals
were probably 20 cm or more in length in the behavioral experiments, an
applied field of 0.01 pV/cm would result in a stimulus to these receptors
of 0.2 pV or more.
The Gymnurchus studied by Machin and Lissmann (1960 ) was
sensitive to fields of about 0.15 pV/cm, and a slightly higher threshold
was calculated for distortions of fields produced by objects. Since the
animal was about 50 cm in length, the field strength would result in a
receptor stimulus of about 4 pV. The thresholds of receptors in Gymnurchus have not been well studied, but the required sensitivity is only
10-20 times greater than is observed in small (tonic) receptors in mormyrids. In Gymnarchus the threshold for high frequency rectangular
pulses is given by the dc component of the stimuli. This observation
indicates that the phasic receptors are no more sensitive to the ac component of this form of stimulus than the tonic receptors are to the dc
component ( granted that these classes of receptor exist).
The catfish Clarias has been shown to be sensitive to a gradient of
about 1 pV/cm in training using food reinforcement (Lissmann and
Machin, 1963). For a 20-cm animal this would correspond to a receptor
stimulus of about 10 pV assuming that the skin is of high resistance.
Receptor thresholds 5-10 times this value have been observed in the
transparent catfish Kryptopterus ( Bennett, 1971a,b).
In mormyrids, threshold gradients along the entire fish for electric
pulses to evoke changes in organ discharge frequency are about 0.05