Camouflage Strategies in Cryptic Predatory Fishes

Abstract

For a successful hunt, marine sit-and-wait predators such as the scorpionfishes need to be well camouflaged in the eyes of their prey. While scorpionfishes are indeed cryptic to the human eye, there is barely any research on the functionality of their camouflage in a preypredator context. Therefore, my research investigated camouflage strategies in two scorpionfish species under consideration of the prey’s visual perspective. I focussed on the question how scorpionfish can camouflage in a heterogeneous environment with a variety of backgrounds, such as different kinds of substrates. In camouflage research, three main strategies are discussed as a solution to this problem. First, animals could dynamically adjust their body colour and pattern depending on their background. Second, animals might choose to settle on backgrounds on which they are best camouflaged and avoid others. Third, animals could have a generalist body colouration that allows camouflage on many natural substrates and therefore mitigates the need to employ dynamic camouflage strategies such as colour change and background choice. In two experiments, I placed scorpionfish on different backgrounds and documented changes in body colouration over one to five minutes using calibrated photography. I used visual modelling to process the images accounting for the visual system properties of prey fishes as naturally relevant observers. I confirmed that scorpionfish dynamically change their body colouration in response to their background, including body hue, luminance, and pattern contrast. In two behavioural choice experiments, I then tested whether scorpionfish prefer to settle on backgrounds that facilitate camouflage. Here, scorpionfish did not choose the background that provided the best background match for their average body colouration, but preferred the background that allowed disruptive colouration. Finally, using data of average scorpionfish body colouration and photographs of natural substrates, I calculated how well scorpionfish would match these substrates from the prey’s perspective. I can show that even without adjustment, scorpionfish have low chromatic (colour) contrast to natural substrates, but high achromatic (luminance) contrast. I demonstrate that scorpionfish show several strategies to camouflage in heterogeneous environments. I discuss how they might interact and interpret the importance of achromatic and chromatic cues for camouflage in these fishes.