Subterranean Fishes of the World

4571

2011

Investigative Ophthalmology and Visual Science

4076

52

Purpose: : Many troglomorphic fish often have enhanced sensory mechanisms for spatial location. Often, the eyes are reduced in size and/or embedded deeply in connective tissue. Our aim is to compare the ocular anatomy in six species of troglomorphic fish in which there is ocular reduction and enhancement of other sensory mechanisms. Methods: : We obtained formalin fixed specimens of the mormyrid Gnathonemus petersii, the Mexican blind cavefish Astyanax sp, and its sighted surface morph, plus four species from the Lower Congo River: Lamprologus lethops and its sighted sister species Lamprologus tigripictilis, the mastacembelid Mastacembelus brichardii, and the clariid Platyallabes tihoni. Ocular tissues from all species were cut in transverse step sections, and stained with hematoxylin and eosin. Results: : The mormyrid elephant-nose fish, Gnathonemus petersii , has a tiny eye in comparison to other surface fish. It has a tapetum in which the rods are embedded in clusters which function as a unit. The Congo River fish show a variety of ocular anatomy. The deep river blind fish, Lamprologus lethops, has small eyes embedded deep in the skull beneath bone and skin. No extra ocular muscles or choroidal rete mirabilis were evident. Morphometric measurements by MLJS demonstrate an enlarged laterosensory canal system in this fish as compared to L. tigripictilis , it’s surface-dwelling, sighted sister species. Mastacembelus brichardii, which lives under rocks and boulders, has a deeply recessed small eye with a well-developed retina. Platyallabes tihoni occupies roughly the same niche in the Congo River as M. brichardii, yet has a functional cornea. This species does have sensory barbells, which may compensate for the decreased vision in the dark, allowing it to locate prey. In Astyanax, the globe is recessed only slightly with skin growing over the surface, allowing more surface area for increased olfaction. Conclusions: : In widely different ecological niches, a variety of selective pressures exist, resulting in the evolution of different sensory modes for mate selection and spatial location.

8

ARVO Annual Meeting Abstract April 2011