Why do electric fishes swim backwards? An hypothesis based on gymnotiform foraging behavior interpreted through sensory constraints

Abstract

SynopsisFishes producing high-frequency wavelike electrical discharges maintain a relatively rigid body axis and swim forwards and backwards with equal ease. Using stop-action videotape filming we have observed the gymnotiform Apteronotus albifrons feeding on zooplankton and oligochaete annelids. Here it is reported that reverse swimming is characteristic of two foraging behaviors: searching for prey and assessing it. In assessing a potential prey item, fish typically scan it from tail to head by swimming backwards, then ingest it after a short forward lunge. A scan in the opposite direction -from head to tail by forward swimming-would have the prey located near the tail and out of position for the final lunge. Food choice experiments indicate that these electrosensing fish feed equally well, and take larger rather than smaller zooplankton, under light and dark conditions. Furthermore, electric fish take normal (light) colored and darkened prey (Daphnia) in a 50 : 50 ratio under both dark and light conditions. These results are consistent with the interpretation that electrosensory cues are being used to detect zooplankton and other prey. Together, our observations support Lissmann's (1958Lissmann's ( ,1974 and Lissmann & Machin's (1958) assertion that backwards swimming is a component of a locomotory pattern guided by the constraints produced by an active electrical sense.

Sensory flow shaped by active sensing: sensorimotor strategies in electric fish

“…The active placement of fovea-like sensory structures, as described for the dorsal filament in prey-capture behavior of A. albifrons, is also evident in the 'side-searching' behavior (Lannoo and Lannoo, 1993). This behavior is exclusively linked to foraging.…”

“…Bastian, 1995;Bastian, 1999;Sawtell, 2010). Coincidence of these centrally Lannoo and Lannoo, 1993;MacIver et al, 2001;Pusch et al, 2008 Relative motion (va-et-vient) Shift spatiotemporal dynamics of sensory input towards the dynamic range of the sensory system, generation of temporal slopes Babineau et al, 2007;Hofmann et al, 2013;Sim and Kim, 2012;Stamper et al, 2012;Toerring and Belbenoit, 1979 Relative motion (tail bending) Change in contrast, calculation of lateral distance by temporal slope ratio Bacher, 1983;Behrend, 1984;Heiligenberg, 1975;Stamper et al, 2012;Sim and Kim, 2011 Control the amount of change of the incoming sensory input Arnegard and Carlson, 2005;von der Emde, 1992 In the left column, text in parentheses indicates exemplary probing motor acts that can be attributed to the strategy. Studies where aspects of these behaviors have been addressed are shown to the right.…”

Ecomorphological relationships of fish assemblages in a trans-Andean drainage, Upper Magdalena River Basin, Colombia

“…It has an elongated body, reduced pectoral fins, prolonged anal fin and lack of dorsal and caudal fin (Maldonado-Ocampo et al, 2005). These morphological features allow this knifefish to swim forward, backward or stay stationary (Lannoo, Lannoo, 1993;Ferreira, 2007), which would facilitate its survival in the pools among the roots of riparian vegetation (Ferreira, 2007;López-Delgado, 2013).…”

Target Detection, Image Analysis, and Modeling

“…When weakly electric knifefish capture prey, they usually do so by swimming backwards (Lannoo and Lannoo 1993;MacIver et al 2001). During the search phase, prior to detection, the fish is often swimming forwards.…”