Can the Dynamic Colouration and Patterning of Bluelined Goatfish (Mullidae; <b><i>Upeneichthys lineatus</i></b>) Be Perceived by Conspecifics?

Bluelined goatfish (<i>Upeneichthys lineatus</i>) exhibit dynamic body colour changes and transform rapidly from a pale, buff/white, horizontally banded pattern to a conspicuous, vertically striped, red pattern when foraging. This red pattern is potentially an important foraging signal for communication with conspecifics, provided that <i>U. lineatus</i> can detect and discriminate the pattern. Using both physiological and behavioural experiments, we first examined whether <i>U. lineatus</i> possess visual pigments with sensitivity to long (“red”) wavelengths of light, and whether they can discriminate the colour red. Microspectrophotometric measurements of retinal photoreceptors showed that while <i>U. lineatus</i>lack visual pigments dedicated to the red part of the spectrum, their pigments likely confer some sensitivity in this spectral band. Behavioural colour discrimination experiments suggested that <i>U. lineatus</i>can distinguish a red reward stimulus from a grey distractor stimulus of variable brightness. Furthermore, when presented with red stimuli of varying brightness they could mostly discriminate the darker and lighter reds from the grey distractor. We also obtained anatomical estimates of visual acuity, which suggest that <i>U. lineatus</i> can resolve the contrasting bands of conspecifics approximately 7 m away in clear waters. Finally, we measured the spectral reflectance of the red and white colouration on the goatfish body. Visual models suggest that <i>U. lineatus</i> can discriminate both chromatic and achromatic differences in body colouration where longer wavelength light is available. This study demonstrates that <i>U. lineatus</i> have the capacity for colour vision and can likely discriminate colours in the long-wavelength region of the spectrum where the red body pattern reflects light strongly. The ability to see red may therefore provide an advantage in recognising visual signals from conspecifics. This research furthers our understanding of how visual signals have co-evolved with visual abilities, and the role of visual communication in the marine environment.