Spatial aggregation and resting places of Apteronotus galvisi (Apteronotidae: Gymnotiformes) individuals in a stream in the Orinoquia region (Meta: Colombia)

Abstract

Weakly electric fish navigate and communicate by using Electric Organ Discharges (EODs). EOD emission depends on internal and external factors and is used to study the biology of these organisms. Recent studies have evaluated distribution and territoriality in some Apteronotus species, but more studies are needed to better comprehend their ecology and behavior under natural conditions. Keeping this in mind, we used fish-finder amplifiers and a GPS to locate, sex and geoposition resting places of Apteronotus galvisi individuals in a 96-m section of a stream located in San Martin (Meta) from September to November 2022. We also made 24-hour EOD recordings ensuring this tracking method accurately identifies fish regardless of water temperature. We found an average of 49 individuals in the sampled area, with a proportion of mature males:females/immature of ~1:6. In the sampled section of the stream, we found a clustered distribution of fish in their resting places, and a majority of males retained their resting places during the sampled months. The effect of water temperature on EOD frequency of A. galvisi was established by calculating the temperature coefficients (Q10) under natural conditions. We were unable to track females/immature individuals due to the overlapping in EOD frequency ranges in clustered areas of the stream. In conclusion, through non-continuous surveys of A. galvisi in their natural habitat we found a skewed sex ratio, a clustered pattern of spatial distribution of their resting places, and males with fixed territories.