The development of the eye in Astyanax mexicanus (Characidae, Pisces), its blind cave derivative, Anoptichthys jordani (Characidae, Pisces), and their crossbreds. A scanning- and transmission-electron microscopic study

Abstract

The development of the eye of the characin Astyanax mexicanus, of its blind derivative Anoptichthys jordani, and crossbreds of both forms was studied at different ontogenetic stages by means of scanning- and transmission-electron microscopy. Astyanax exhibits a form of eye development resembling that in other characid species. A severe reduction of the eye could be observed in Anoptichthys starting with the second day of ontogeny. This degenerational process is characterized by the following features: 1) An overgrowth of epidermal tissue that gradually covers the surface of the eyeball; 2) the sinking of the eyeball below the surface of the integument; 3) the formation of epidermal channels from the body surface to the disappearing surface of the eyeball; 4) a severe degeneration of the retinal sensory cells; and 5) a small number of pigment granules in the pigment epithelial cells. The progeny of crosses between Astyanax and Anoptichthys show varying degrees of these degenerational signs. Taste buds and the lateral line organ display identical features in all crosses analyzed with the scanning electron microscope.