High-resolution behavioral mapping of electric fishes in Amazonian habitats

Abstract

The study of animal behavior has been revolutionized by sophisticated methodologies that identify and track individuals in video recordings. Video recording of behavior, however, is challenging for many species and habitats including fishes that live in turbid water. Here we present a methodology for identifying and localizing weakly electric fishes on the centimeter scale with subsecond temporal resolution based solely on the electric signals generated by each individual. These signals are recorded with a grid of electrodes and analyzed using a two-part algorithm that identifies the signals from each individual fish and then estimates the position and orientation of each fish using Bayesian inference. Interestingly, because this system involves eavesdropping on electrocommunication signals, it permits monitoring of complex social and physical interactions in the wild. This approach has potential for large-scale non-invasive monitoring of aquatic habitats in the Amazon basin and other tropical freshwater systems.

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

“…Sternopygus: n = 69, Eigenmannia: n = 49, Apternonotus: n = 10. brief recordings in the field (Madhav et al, 2018). In our present study and in Henninger et al (2018), we scaled this approach up to obtain data on natural behaviors of freely moving weakly electric fish in the field over extended periods of time.…”

“…A critical problem for temporal tracking wave-type electric fish are EOD frequencies that approach, or even cross, each other. This is not a particular problem in the data set introduced here, but could easily occur at larger fish densities or with social fish like Eigenmannia (Henninger, 2015;Madhav et al, 2018). This issue can, to a certain extent, be be resolved by taking the spatial distribution of power at a given frequency into account (Madhav et al, 2018).…”

“…the water conductivity (inversely proportional). The electric organs of weakly electric fish can be approximated as constant current sources (Knudsen, 1975) and therefore P is proportional to the current produced by the electric organ and inversely proportional to the conductivity of the water (Madhav et al, 2018). For estimating the position, orientation, and EOD amplitude of a fish we fitted the absolute value of the dipole model Eq.…”

“…In contrast, EOD-based tracking exclusively relies on the fish's own, continuously emitted signals and therefore does not disturb the animals. This tracking approach allows for following individuals over time (Madhav et al, 2018), provides direct access to the fish's communication signals (Henninger et al, 2018), and excels in terms of sub-second temporal resolution and a decent spatial resolution of about 10 cm. However, physical interactions like mouth wrestling or tail nipping, which could easily be detected visually in the lab (Triefenbach and Zakon, 2008), are inaccessible and can only be inferred indirectly, if at all, from EOD signals, context, and movement dynamics.…”

“…By recording their EODs with distributed electrodes (Fig. 1 B) -as has been suggested by Hagedorn and Heiligenberg (1985) and tested in the lab (Jun et al, 2013;Matias et al, 2015) and in the field (Madhav et al, 2018) -it is possible to track individual fish in their natural habitats without the need to tag them (Henninger et al, 2018). Such recordings pick up the EODs of all electric fish species present in the recording area.…”