Dynamic color change in the grouper Variola louti during interspecific interactions and swimming

Animals can change their body color for various ecological functions. In
fish, rapid dynamic color change is primarily known in contexts of
intraspecific communication and camouflage, while examples in
interspecific contexts are rare. We studied dynamic color changes and
their associated behaviors in the grouper Variola louti in its native
coral reef environment in the Red Sea. Using underwater videos to record
natural behaviors and color-calibrated still images to measure body
colors, we quantified color displays as the brightness of the body and the
contrast of three distinct patterns: body patches, head stripe, and side
bars. V. louti exhibited a diverse range of pattern displays, which
rapidly transformed according to its behavioral shifts. A high-contrast
head stripe pattern was observed when V. louti engaged in agonistic
interspecific interactions, but was interestingly absent when hunting
alone or in cooperation with moray eels. The brightness of V. louti’s body
color and the contrasts of the body patches and side bars were associated
with its swimming behavior. Darker body colors and high contrast body
patches and side bars were expressed when the fish rested on the bottom,
whereas bright and uniform body colors were displayed when swimming higher
above the reef. Our results suggest that V. louti utilizes dynamic color
displays for camouflage and interspecific communication in agonistic and
competitive interspecific interactions. These findings highlight the
importance of dynamic color changes for communication and provide valuable
insights into the behavioral ecology of animals.