1. The ability to see ultraviolet (UV) light (<400 nm) may have importance for foraging, communication or navigation in many taxa including insects, crustaceans, fishes, amphibians, reptiles, birds and mammals. Behavioural experiments reveal how vision mediates such behaviour; however, our knowledge of UV perception is constrained by the challenge of creating and calibrating stimuli that reflect or emit UV. Commonly used technologies for displaying visual stimuli-such as computer screens and printers-are designed for human vision and thus are unsuitable for testing UV perception. 2. To overcome this limitation, we designed and constructed a display with five spectral channels with peak wavelengths as follows: red at 629 nm, green at 526 nm, blue at 466 nm, violet at 395 nm and UV at 367 nm. Each pixel of the display consists of five LEDs with a baffle to prevent crosstalk from adjacent pixels and a diffuser to promote uniform colour mixing. The LEDs are driven by high-performance pulse-width-modulated constant-current drivers with a maximum flicker rate of 64 kHz and a maximum frame rate of 6.5 kHz. This method allows colour mixing with wavelengths as low as 350 nm to be calibrated and tested rapidly and concurrently. 3. To demonstrate the utility of this display, we conducted colour detection tests using the anemonefish, Amphiprion ocellaris, a species known to have UV-sensitive cones. Fish were able to associate pecking all target colours ('Blue', 'UV-grey' and 'UV') with a food reward, demonstrating for the first time, UV perception in A. ocellaris. 4. The RGB-V-UV LED display is a useful device for behavioural tests of colour vision across a broad spectrum (350-650 nm) visible to many animals and can be used to investigate various questions concerning animal perception, including colour discrimination and categorisation. We include design documents and source code so this system can be further developed and modified to investigate other visual behaviours in a variety of taxa. K E Y W O R D S animal behaviour, colour vision, coral reefs, ultraviolet vision, visual ecology This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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In many animals, ultraviolet (UV) vision guides navigation, foraging, and communication, but few studies have addressed the contribution of UV vision to color discrimination, or behaviorally assessed UV discrimination thresholds. Here, we tested UV-color vision in an anemonefish (Amphiprion ocellaris) using a novel five-channel (RGB-V-UV) LED display designed to test UV perception. We first determined that the maximal sensitivity of theA. ocellarisUV cone was at ~386 nm using microspectrophotometry. Three additional cone spectral sensitivities had maxima at ~497, 515, and ~535 nm, which together informed the modelling of the fish's color vision. Anemonefish behavioral discrimination thresholds for nine sets of colors were determined from their ability to distinguish a colored target pixel from grey distractor pixels of varying intensity. We found thatA. ocellarisused all four cones to process color information and is therefore tetrachromatic, and fish were better at discriminating colors (i.e., color discrimination thresholds were lower, or more acute) when targets had UV chromatic contrast elicited by greater stimulation of the UV cone relative to other cone types. These findings imply that a UV component of color signals and cues improves their detectability, that likely increases the salience of anemonefish body patterns used in communication and the silhouette of zooplankton prey.

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