Red fluorescence in a signalling context. a-b. Frameshots of two videos suggestive of communication involving fluorescent fins. a. Enneapterygius destai waving its first dorsal fin when 'excited' (laboratory, from Additional file 3, sequence 2b). b. Corythoichthys schultzi pair interacting, displaying conspicuous red fluorescence on the tail plate (natural reef illumination, 20 m depth, from Additional file 3, sequence 1). c. Ctenogobiops maculosus is cryptic when sitting at its burrow entrance under natural illumination (insert), but shows conspicuous eyes when emphasizing red wavelengths (Additional file 2). d. Bryaninops natans with a pupil-like black spot on the upper part of the fluorescent eye ring suggesting that fluorescence and (deceptive) gaze signalling may be linked in this species (Additional file 2).