Spectral sensitivity of the Hawaiian saddle wrasse, Thalassoma duperrey, and implications for visually mediated behaviour on coral reefs

Although tropical coral reefs are one of the most spectrally complex habita ts, there is relatively little known about colour vision of reef fish. In t his study, we measured the spectral sensitivity of an endemic Hawaiian cora l reef fish, Thalassoma duperrey (family Labridae), and assessed the possib le role of visual sensitivity in mediating intraspecific communication. Ele ctrophysiological recordings of compound action potentials from retinal gan glion cells were used to generate spectral sensitivity curves for specific wavelengths (380-620 nm). We found at least 2 sensitivity peaks for the on response (lambda(max)=460, 550 nm). The off response lacked a short wavelen gth mechanism but a medium wavelength mechanism (lambda(max)=545 nm) and a longwave mechanism (lambda(max)=570 nm) were found. To quantify the visual stimulus provided by a conspecific individual, spectral reflectance from th e colour pattern of T. duperrey was measured with a spectroradiometer. Lumi nance and spectral contrast were computed between colour patches of the pat tern and between the patches and natural backgrounds (i.e., water and coral ). Reflectance from the blue head and contrast from the blue, green and red patches matched the sensitivity maxima of T. duperrey, although this depen ded on the type of background. Our results indicate that T. duperrey should be able to visually detect the colour pattern of a conspecific fish and th at T. duperrey's visual system is designed to enhance target detection in t he coral reef habitat with matched and offset cone mechanisms.