1/28/2024 0 Comments Signalscope electric fishBy convention, head-positivity is always plotted upward.īecause the electric organ approximates a dipole source, positioning the electrodes anywhere near the fish will give you the same EOD waveform, although the amplitude of the EOD waveform will diminish as the fish's body axis becomes more oblique to the axis of the electrodes and will invert when the fish goes past perpendicular and switches head-tail orientation with respect to the electrodes. The voltage axis is arbitrary, since the distance between fish and electrodes is variable. The voltage between the two electrodes is amplified, recorded, and viewed. EOD waveforms are usually shown as oscilloscope tracings, or oscillograms, with time on the X-axis and voltage on the Y.ĮODs are recorded by placing wire electrodes at both ends of the fish (see the earlier blog article on electrode wand construction below). The waveform of an individual EOD pulse, however, remains fixed from moment to moment and its duration and shape often reflects the species and sex of the signaler (Friedman & Hopkins, 1996 Hopkins & Bass,1981). A mormyid changes the interval between the pulses (called the "sequence of pulse intervals" or SPI) in stereotyped ways to communicate its intentions (aggression, submission, courtship, etc.) to neighboring fish. These brief (0.25-10 millisecond) electric pulses are too weak to be felt by touch (although catch a large Mormryrus and place your hand near its tail in the water and report back!), but they are easily monitored by a small amplified speaker (see article below) or recorded. Mormyrids continuously produce weak electric organ discharges or EODs from an organ in their caudal peduncle. In this article I will indicate a couple of simple ways to make high quality EOD recordings. Recording EODs is especially important when species identity of the fish is in doubt and when the specimens could represent new taxa. Ideally, more researchers should be recording EODs when they collect mormyrids in the field, particularly as it is no longer so difficult to do and the size and expense of the required equipment is now rather modest. Feel free to leave your comments or questions.īecause of their frequent species-specificity, the value of EOD waveforms in mormyrid taxonomy has long been recognized. I'll update this article as needed to keep it current and maximally helpful. What I know about EODs and recording them I've learned from Professor (now Emeritus) Carl Hopkins of Cornell University and from experience on more than one dozen field trips to Africa. This is written with mormyrids in mind, but most of this will also hold for recording EODs from gymnotiform fishes in Central & South America. Here I lay out how I record the electric organ discharges (EODs) of mormyrids and offer some advice on how you can do so yourself.
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