ABSTRACT
Subterranean or hypogean fi shes are herein defi ned as those living in [an occluded, semi-occluded] a cave or subterranean river system during their whole life. Among these, species restricted to subterranean habitats (troglobites) usually show a series of autapomorphies (troglomorphisms), including morphological, physiological, behavioral and ecological features, which can be directly or indirectly related to the hypogean life, being either adaptive or not (Trajano 2001). The most common morphological traits characterizing cavefi shes and other troglobites are the reduction of eyes and pigmentation when compared to their surface relatives. Eyes are vestigial or absent and dark pigmentation may reduce to the point that the body appears to be transparent. In addition, the numbers and sizes of mechano-and chemo-reception organs are often increased (Greenwood 1967, Chen et al. 1997, Chen et al. 1998, Chen et al. 2001). To a certain degree, it can be said that cavefi shes are living fossils in the process of evolution (Chen et al. 2001). Because of their unusual appearance, local people also call them “transparent fi shes”, “glass fi shes”, “blind fi shes” or “eyeless fi shes”. Hypogean fi shes have always been a source of amazement and amusement throughout the history of ichthyology (Romero and Paulson 2001).
