A comparative study on the visual adaptations of four species of moray eel.

The goal of this study was to investigate how the eyes of different species of moray eel evolved to cope with limitations to vision imposed on them by the photic environments in which they reside. The comparative retinal histological structures and visual pigment characteristics including opsin gene sequences, of four species of moray eel inhabiting diverse habitats (i.e., shallow-water species, Rhinomuraena quaesita and Gymnothorax favagineus, and deep-sea species, Gymnothorax reticularis and Strophidon sathete) were examined. The histological sections showed that retinal layer structures of R. quaestia are significantly different from those of the other three species which likely reflects the effects of distribution depth on the structures. The maximal absorbance wavelength (λ(max)) of photoreceptor cells, as measured by microspectrophotometry (MSP), showed a close correlation between the λ(max) and the intensity/spectral quality of the light environment where each species lives. The spectra-shift, between shallow and deep-sea species, observed in the rods cells results from amino acid substitution in Rh1 gene, while that in cones most likely results from differential expression of multiple Rh2 genes.