Vision and visual variation in the peacock blenny

Microspectrophotometry (MSP) revealed the presence of a rod and at least two cone classes (mid- and long-wavelength sensitive) in the intertidal peacock blenny Salaria pavo. Both rhodopsin and porphyropsin based visual pigments were found in all fish, together with high individual variation in the chromophore ratio. The three morphs (females, males and sneaker males) differed in their spectral sensitivities (as measured with the optomotor response) with sneakers having higher sensitivity at long-wavelengths than either males or females. This long-wave displacement of peak sensitivity could be due to elevated proportions of porphyropsin visual pigments in the sneakers' retinae. The lenses of all morphs exhibited a short-wavelength cut-off and an unusual layer of carotenoid was found behind the retinal pigment epithelium and in the outer segments of some cones. These screening pigments could serve a photo-protective role or to improve visual contrast. No short-wave photoreceptors were located using MSP. This indicates that this cone class may be absent or present at very low numbers in the retina. This is the first in depth study of the visual system of a blenniid fish and indicates potential within-species visual variation that may be related to the species' habitat and morph-specific behavioural requirements.