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C. S. Schobert, I. R. Schwab, M. L. J. Stiassny, R. C. Schelly, J. H. Lowenstein, C. Zeiss, R. R. Dubielzig; Comparative Ocular Anatomy in a Blind African Cichlid Fish, Lamprologus lethops. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6332.
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We describe the gross and microscopic anatomy of ocular structures of the albino, blind cichlid, Lamprologus lethops, and its putative sister species, Lamprologus tigripictilis. The two are sympatric and endemic to the Lower Congo River rapids.
An individual was fixed and processed for paraffin sectioning. Five-micron sections, including all ocular structures, were stained with H&E. Samples of the closely related, sighted congener, L. tigripictilus, were treated in the same manner. Immunohistochemical staining for rhodopsin markers was also performed.
Anatomical features of L. lethops included a diminished globe diameter. Although the scleral profile maintained a spherical shape, much of the choroid was occupied by adipose tissue containing no choroidal gland. In L. tigripictilus, no adipose tissue is seen within the choroid, and a choroidal gland is present. The optical globe was foreshortened in the A-P dimension and deviated dorsally towards the midline with no extraocular muscles. Globes were surrounded behind the posterior pole by an open periocular space with no cell bodies. Similar to other teleosts, the sclera contains cartilage. The L. lethops lens appeared as fully developed as in its sighted congener, but the size of the lens in the former is not consistent with Matthiessen’s ratio. The cornea has an intact scleral layer but no trace of a dermal layer. Instead, the globe is situated beneath bone and skin. The retina of L. lethops was thin and the ONL had 2 layers compared with 4 in L. tigripictilus. The inner and outer segments were barely discernable; however rhodopsin was present in both species in comparable amounts.
Troglomorphic fishes provide excellent comparative models with which to study convergent and divergent evolution of the eye.
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