Data from: Red fluorescence of the triplefin Tripterygion delaisi is increasingly visible against background light with increasing depth

The light environment in water bodies changes with depth due to the
absorption of short and long wavelengths. Below 10 m depth, red
wavelengths are almost completely absent rendering any red-reflecting
animal dark and achromatic. However, fluorescence may produce red
coloration even when red light is not available for reflection. A large
number of marine taxa including over 270 fish species are known to produce
red fluorescence, yet it is unclear under which natural light environment
fluorescence contributes perceptively to their colours. To address this
question we: (i) characterized the visual system of Tripterygion delaisi,
which possesses fluorescent irides, (ii) separated the colour of the
irides into its reflectance and fluorescence components and (iii) combined
these data with field measurements of the ambient light environment to
calculate depth-dependent perceptual chromatic and achromatic contrasts
using visual modelling. We found that triplefins have cones with at least
three different spectral sensitivities, including differences between the
two members of the double cones, giving them the potential for
trichromatic colour vision. We also show that fluorescence contributes
increasingly to the radiance of the irides with increasing depth. Our
results support the potential functionality of red fluorescence, including
communicative roles such as species and sex identity, and
non-communicative roles such as camouflage.