Visual ecology of Australian flathead

Despite our growing understanding of fish visual ecology, the visual systems of relatively few benthic marine species have been described in detail. Flatfish are one of the largest groups of benthic fish, and in the New South Wales (NSW) region of the East coast of Australia, the Platycephalidae (flatheads) are the predominant and most diverse flatfish family. Flatheads are also important economically, accounting for $2.1 million in NSW fisheries revenue annually. The aim of this study was to investigate the anatomy and spectral sensitivity of the eyes of flatheads to identify correlations with habitat and behaviour, using one or more of the species found in NSW waters. Microspectrophotometry (MSP) was used to measure the spectral absorbance properties of the visual pigments in the rod and cone photoreceptors of the dusky flathead (Platycephalus fuscus) and blue-spotted flathead (Platycephalus caeruleopuntatus). The MSP data show that P. fuscus, which predominantly occupies shallow estuarine habitats, possesses multiple cone visual pigments with peak sensitivities in the short ('blue') to medium ('green') wavelength range of the spectrum. MSP data of P. caeruleopuntatus, which predominantly occupy deeper water marine habitats, shows that they possess similar multiple cone visual pigments to P. fuscus, but with a noticeable shorter wavelength shift in the single cone visual pigment. Spectrophotometry of the ocular media of both species reveals that the spectral absorbance of the lens limits the transmission of short wavelength light to the retina and effectively blocks wavelengths below about 400 nm. The topographic distribution of retinal neurons was also measured to establish the areas of the visual field sampled with high resolution. P. fuscus and P. caeruleopuntatus display a similar distributional topography with an elongated area present in the dorsal retina. The results of this study are compared with findings for other benthic fish species.