Preferência de cor e brilho em substrato pelo peixe elétrico Sul-Americano Ituí-Cavalo (Apteronotus albifrons)

Abstract

The Gymnotiform weakly electric fishes are widely used as animal models for studies in electrocommunication. The theoretical body regarding the vision of these animals is scarce, since their eyes are less developed than their electric sense. In comparison to the physiological evidence from the Gymnotiform Eigenmannia virescens, it is believed that the South American electric fish Ituí-cavalo (Apteronotus albifrons) is a long-wavesensitive cone monochromat. However, no experiment demonstrated the color perception in this animal by behavioral basis so far, nor was the influence of the brightness cue on its natural behavior investigated. In the present study, we tested eight Ituí-cavalos in the UFRN Sensory Ecology laboratory on preference for brightness and color by comparisons on backgrounds. We selected the stimuli after visual modeling for the photopic (high light intensity) and mesopic (intermediate light intensity) vision of the fish under 800 and 8 lux, respectively. We referenced the brightness parameters at 40, 65, 70 and 100% to the gray color reflectance standard, while the chromaticity parameters were 100% of the reflectance pattern of yellow and green colors. We divided circular backgrounds into three equal parts, one for the brightness experiment, divided into gray40 (dark), gray70 (intermediate) and gray100 (light), and one for color test, divided into yellow100, green100 and gray65. We controlled the grays used in the brightness test for the same chromatic value and varied only in achromatic value, inciting discernment based solely on the brightness cue; in the color test, we controlled all colors for the same achromatic value and only varied in chromatic value, guaranteeing that the animal would only differentiate them if it had color vision. We recorded the time spent/area of the stimulus as a deterministic parameter of preference. The results showed that the Ituícavalo had a populational preference for darker shades, avoiding the lightest one, and that the possible color preferences were individual, without any discernible pattern. The preference for dark backgrounds can be justified as a possible maneuver to reduce stress and/or risk of predation, as observed in Heterandria formosa, while color preference rests on a possible visual modeling mismatch of visual modeling outlined for the Ituí-cavalo. These findings demonstrate the importance of behavioral experimentation for the practical verification of physiological studies.