10. ELECTRIC ORGANS
409
Fig. 35. Responses recorded in head region of Steatogenys elegans. Methods
as for Fig. 30. The dotted lines indicate the sites of recording of the various traces.
The three traces with arrows are recorded 2.5 cm rostral to the snout, 4.5 cm
caudal to the snout and near the tip of the tail. There are large early negativities
external to the rostral end of the submental organ and external to the caudal end
of the postopercular organ. There are corresponding positivities just inside the
mouth and gill opening.
phasic action potentials. The related genus Rhumphichthys has not been
studied with respect to its electric organs.
f. Sternopygus and Eigenmunnia. Sternopygus and Eigenmannia are
closely related and the organ discharges are so similar that they may be
considered together. The discharges consist of head-positive pulses
superimposed on a head-negative base line such that there is little dc
component in the organ discharge; that is, averaged over one discharge
cycle, there is little or no net current flow (Fig. 3C). The frequency in
Sternopygus is about 5&100/sec, and in Eigenmannia it is about 2506OOIsec.
The frequency is quite constant, and ordinary forms of stimulation do
not affect it. Weak electric stimuli of nearly the same frequency as the
animal‘s own discharge evoke the “jamming avoidance” response, that is,
a small shift in frequency away from that of the interfering stimulus
(Watanabe and Takeda, 1963; Bullock, 1970; see Chapter 11, this
volume). Sternopygus can also stop discharging completely under these
conditions.
The electric organ is located in the same position as in Hypopomus
409
Fig. 35. Responses recorded in head region of Steatogenys elegans. Methods
as for Fig. 30. The dotted lines indicate the sites of recording of the various traces.
The three traces with arrows are recorded 2.5 cm rostral to the snout, 4.5 cm
caudal to the snout and near the tip of the tail. There are large early negativities
external to the rostral end of the submental organ and external to the caudal end
of the postopercular organ. There are corresponding positivities just inside the
mouth and gill opening.
phasic action potentials. The related genus Rhumphichthys has not been
studied with respect to its electric organs.
f. Sternopygus and Eigenmunnia. Sternopygus and Eigenmannia are
closely related and the organ discharges are so similar that they may be
considered together. The discharges consist of head-positive pulses
superimposed on a head-negative base line such that there is little dc
component in the organ discharge; that is, averaged over one discharge
cycle, there is little or no net current flow (Fig. 3C). The frequency in
Sternopygus is about 5&100/sec, and in Eigenmannia it is about 2506OOIsec.
The frequency is quite constant, and ordinary forms of stimulation do
not affect it. Weak electric stimuli of nearly the same frequency as the
animal‘s own discharge evoke the “jamming avoidance” response, that is,
a small shift in frequency away from that of the interfering stimulus
(Watanabe and Takeda, 1963; Bullock, 1970; see Chapter 11, this
volume). Sternopygus can also stop discharging completely under these
conditions.
The electric organ is located in the same position as in Hypopomus