Knollenorgan receptors are electrically tuned to frequencies between 100 Hz and 20,000 Hz depending upon the species. The plots below show a close correspondance between the electroreceptor tuning and the power spectrum of the EOD.
The plot to the left shows the tuning curves of Knollenorgans from Brienomyrus brachyistius TP . The EOD of the female is shown in the inset along with the Fourier Transform of the EOD. The peak of the power spectrum is at about 1.5 k Hz
Tuning curves are shown in the second pannel. There are two types of receptors: high frequency receptors are tuned to 1.5 kHz; low frequency receptors are tuned to 500 to 1000 Hz.
A histogram of knollenorgan best frequencies shows two populations, one high frequency one low.
The fish at the bottom shows the positions of the receptors on the body surface.From Hopkins (1983)
Low frequency knollenorgans are located on the opercular flap and on the underside of the head. High frequency knollenorgans are located elsewhwere on the body surface.
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