Elektroortung bei schwach elektrischen fischen: verzerrungen des elektrischen feldes von Gymnotus carapo und Gnathonemus petersii durch gegenstände und ihre wirkungen auf afferente aktivitäten

Abstract

• 1. Discharges of the electric organ (EODs) of the weakly electric fishes Gymnotus carapo and Gnathonemus petersii produce alternative electric fields in the surrounding water. Equipotential contures are plotted in order to know the electric field in detail and to mimic it with a dipol model.

• 2. Either fields are deformed in a characteristic manner by conducting and nonconducting objects. These field distortions, opposite for conductors and nonconductors were measured by using several methods:

  • a) Comparisons of undistorted and distorted field patterns issue variable distortions shapes depending on the objects' placement.

  • b) Direct measurements of field distortions at a “receptor site” were made by several sets of electrodes.

  The effects measured depend on the conductivity of objects, their size and their distance from the electrical dipole the last being due to the inhomogenous field contures. As a general rule, plastic objects make the field increase, and metal objects decrease. However, considering all positions, either material produces complex field variations (di- and polyphasic curves).

• 3. Since responses of gymnotids' primary fibers as a function of plates' position strikingly fit to the curves of field distortion, the electroreceptors use obviously quite similar measurement conditions as the field registration arrangements. This evidence is discussed and compared with more general aspects of field distortions in homogenous fields.

• 4. The field effects decrease exponentially with the lateral distance of objects to the dipole. However, the reaction of primary fibers decreases rather linearly as the lateral distance of objects is increased.

• 5. Experiments with systematically changed stimulus frequency showed primary fibers to be exited over a much wider range of frequencies (0–1000 cps at least) than to be expected regarding the usual EOD discharge rate of 30–100 cps. However, the peak of the “tuning curve” at best frequency fits well into this range. On the other hand, the change of response over this frequency range is 10–20%, so that there is but minor improvement of the information by an increase of EOD frequency.