The slender filefish is a master of adaptive camouflage and can change its appearance within 1–3 s. Videos and
photographs of this animal’s cryptic body patterning and behavior were collected in situ under natural light on a
Caribbean coral reef. We present an ethogram of body patterning components that includes large- and small-scale
spots, stripes and bars that confer a variety of cryptic patterns amidst a range of complex backgrounds. Field
images were analyzed to investigate two aspects of camouflage effectiveness: (1) the degree of colour resemblance
between animals and their nearby visual stimuli; and (2) the visibility of each fish’s actual body outline vs. its
illusory outline. Most animals more closely matched the colour of nearby visual stimuli than that of the
surrounding background. Three-dimensional dermal flaps complement the melanophore skin patterns by
enhancing the complexity of the fish’s physical skin texture to disguise its actual body shape, and the morphology
of these structures was studied. The results suggest that the body patterns, skin texture, postures and swimming
orientations putatively hinder both the detection and recognition of the fish by potential visual predators.
Overall, the rapid speed of change of multiple patterns, colour blending with nearby backgrounds, and the
physically complicated edge produced by dermal flaps effectively camouflage this animal among soft corals and
macroalgae in the Caribbean Sea. © 2015 The Linnean Society of London, Biological Journal of the Linnean
Society, 2015, 116, 377–396.