Electrosensory and metabolic responses of weakly electric fish to changing water conductivity

Abstract

AbstractWeakly electric Gymnotiform fishes use self-generated electric organ discharges (EODs) to navigate and communicate. The electrosensory range for these processes is a function of EOD amplitude, determined by the fish’s electric organ (EO) output and the electrical conductivity of the surrounding water. Anthropogenic activity, such as deforestation, dams, and industrial/agricultural runoff, are known to increase water conductivity in neotropical habitats, likely reducing the electrosensory range of these fish. We investigated whether fish modulate EO output as means of re-expanding electrosensory range after a rapid increase in water conductivity in the pulse-typeBrachyhypopomus gauderioand the wave-typeEigenmannia virescens. Furthermore, because EOD production incurs significant metabolic costs, we assessed whether such compensation is associated with an increase in metabolic rate. Following the conductivity increaseB. gauderioincreased EOD amplitude by 20.2 ± 4.3% over six days but with no associated increase in metabolic rate, whereas the EOD amplitude ofE. virescensremained constant, accompanied by an unexpected decrease in metabolic rate. Our results suggest thatB. gauderiouses a compensation mechanism that requires no metabolic investment, such as impedance matching, or a physiological tradeoff wherein energy is diverted from other physiological processes to increase EO output. These divergent responses between species could be the result of differences in reproductive life history or evolutionary adaptations to different aquatic habitats. Continued investigation of electrosensory responses to changing water conditions will be essential for understanding the effects of anthropogenic disturbances on gymnotiforms, and potential physiological mechanisms for adapting to a rapidly changing aquatic environment.