Active electrolocation of polarized objects by a pulse-discharging electric fish, Gnathonemus petersii

In this article, the ability of Gnathonemus petersii to discriminate object polarity was investigated. According to the article, polarized light can “conduct current differently depending on the direction.” Since G. petersii is a weakly electric fish, the electric EOD’s it produces will be affected by electric polarity. In other words, electric polarity affects the waveform EOD of an electric fish and will therefore make them more sensitive to polarized objects. A series of experiments we used by manipulating changes in a circuit comprised of diodes with various combinations.

Many of the initial experiments were conducted to test G. petersii’s reaction to different types of test circuits, helping the researchers understand the fish’s sensitivity to semiconductor properties. “

Also, a digital oscilloscope was used to sample and monitor the effect of various circuit configurations on EOD waveforms. Using this technique, the researchers were able to record the EOD waveform in the absence of a stimulus component when the circuit was open. When the pole was set closer to the fish, the amplitude of the signal was increased. By subtracting the intact EOD from the different circuit configurations amplitude drop and waveform distortion can be analyzed. The phase, distance, and orientation of the circuit were tested to determine the effect on EOD waveforms.

The array of tests did show that G. petersii detects polarized objects and is able to discriminate between polarity directions. By changing the various circuit configurations the researchers showed that the fish can perceive an object solely by using electrolocation. It was also found that at a transition point for the diode they “always reacted to one polarity direction (Rev), but in the other direction (Dir), the reaction depended on distance. It would also change its discharge rate when confronted with an inversion of diode. These observations allow us to see the sensitivity that G. petersii exhibits when encountering a polarized object. Heightened electric sense is understandable because G. petersii lacks developed eyes therefore visual sense for finding prey and encountering other fish. In dark, deep waters, visual senses would be practically useless. Using these observations, the scientists hoped to accurately “propose behavioral and ecological implications for polarized object sensitivity in G. petersii.

The topic presented here relates greatly to hat we learned in lecture. The article talks significantly about electrolocation, the ability of weakly electric fish to send out electric fields and shortly after receive them. The ability allows the fish to analyze the electric field when it returns and make inferences about the environment. We also talked about polarization in lecture. Although it was in the context of light when we talked about it in lecture, polarization can occur in electric fields also. This article took a commonly discussed sensory modality and used experiments to further investigate its accuracy when other the electric field is strictly polarized.

Avril, A. & Graff, S. (2007) Active electrolocation of polarized objects by a pulse-discharging electric fish, Gnathonemus petersii. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural & Behavorial Physiology, 193.12, 1221-1234.