A new blind cave fish population of genus Astyanax: Geography, morphology and behavior

A new population of blind, cave dwelling tetra fish of the genus Astyanax w as discovered in Granadas Cave, in the Balsas drainage, southern Mexico. Al l blind Mexican tetras previously described are from Tampico and San Luis P otosi, northern Mexico. The discovery of a new blind morph thus represents an independent colonization and convergent adaptation to the cave environme nt by this fish. Individuals of this population display variability of thei r troglomorphic features. Some individuals presented asymmetrical degenerat ion of the eyes, where one was normal, but the other somewhat reduced in si ze and complexity. Loss of pigmentation and eye reduction, although sometim es correlated, were not always linked; reduced eyes were found on pigmented fish and unpigmented fish often possessed normal eyes. Some individuals ha d reduced lens size or an absence of lens altogether. Retina is highly modi fied with photoreceptors sometimes absent. Eye reduction was correlated wit h a diminished size of the optic lobes and an increase of the prosencephalo n. Modifications of the skull involve closing in of the circumorbital serie s of bones. Certain aspects of behavior are also modified.