Tracking activity patterns of a multispecies community of gymnotiform weakly electric fish in their neotropical habitat without tagging

Abstract

Field studies on freely behaving animals commonly require tagging and often are focused on single species. Weakly electric fish generate a species-and individual-specific electric organ discharge (EOD) and therefore provide a unique opportunity for individual tracking without tagging. We here present and test tracking algorithms based on recordings with submerged electrode arrays. Harmonic structures extracted from power spectra provide fish identity. Localization of fish based on weighted averages of their EOD amplitudes is found to be more robust than fitting a dipole model. We apply these techniques to monitor a community of three species, Apteronotus rostratus, Eigenmannia humboldtii, and Sternopygus dariensis, in their natural habitat in Darién, Panamá. We found consistent upstream movements after sunset followed by downstream movements in the second half of the night. Extrapolations of these movements and estimates of fish density obtained from additional transect data suggest that some fish cover at least several hundreds of meters of the stream per night. Most fish, including Eigenmannia, were traversing the electrode array solitarily. From in-situ measurements of the decay of the EOD amplitude with distance of individual animals we estimated that fish can detect conspecifics at distances of up to 2 m. Our recordings also emphasize the complexity of natural electrosensory scenes resulting from the interactions of the EODs of different species. Electrode arrays thus provide an unprecedented window into the so-far hidden nocturnal activities of multispecies communities of weakly electric fish at an unmatched level of detail. Summary statementDetailed movement patterns and complex electrosensory scenes of three species of weakly electric fish were tracked without tagging using a submerged electrode array in a small Neotropical stream.Keywords animal behavior | tracking | weakly electric fish | localization | electrosensory scenes | movements | nocturnal

Adaptive shift of active electroreception in weakly electric fish for troglobitic life

“…Although these fishes use electric fields to detect nearby objects, evidence from catfish are nevertheless consistent with the hypothesis that the generation of weak electric fields evolved in the context of social signaling (Baron et al, 1994;Orlov et al, 2021). Weakly electric fishes detect the electric fields of nearby conspecifics (Heiligenberg, 1991) and the active electric sense is an important channel for social communication between conspecifics (Henninger, 2015;Caputi, 2017;Crampton, 2019). The ancestors of weakly electric fishes had a category of electroreceptors known as ampullary receptors, which detect low-frequency electric signals in the water.…”