Astyanax fasciatus

Astyanax fasciatus species complex (Cuvier, 1819)
Mexican blind/cave tetra
Common Name: Mexican blind/cave tetra (E). Etymology: This epigean form of this species was originally described by Cuvier (1819:352, Pl. 26 [Figure 2]) as Chalceus fasciatus based on material from Brazil. The genus Astyanax was created by Baird & Girard (1854) and then the species was reassigned to it. The specific status of the epigean form in the areas surrounding the cave localities for the troglobitic ones is in dispute. The whole family Characidae is very complex, with many species that are difficult to differentiate from each other and are not always allopatric (Géry 1977, Nelson 1994). New species of the genus Astyanax have been described in Mexico using morphological characters only (e.g., Contreras-Balderas & Lozano-Vilano 1988, Lozano-Vilano & Contreras-Balderas 1990). Common synonyms are A. mexicanus, a rearrangement of Tetragonopterus mexicanus (De Filippi 1853), and Astyanax fasciatus mexicanus. The use of mexicanus has been most commonly employed by US-based authors, especially when dealing with epigean individuals from Texas. However, clear taxonomic differences and geographic limits between A. fasciatus and A. mexicanus have yet to be established. Until the taxonomy of the entire genus is fully clarified, the most parsimonious approach is to use the name Astyanax fasciatus, clarifying when necessary whether we refer to the epigean or troglobitic populations. We avoid the use of the term ‘cave populations’ because some hypogean individuals are actually eyed and pigmented. Major Synonyms: (See the History section below). History: The first cave, troglobitic population (from La Cueva Chica in the San Luis de Potosí area) was described as Anoptichthys jordani (Hubbs and Innes 1936), the second one (from La Cueva El Pachón) was named Anoptichthys antrobius (Alvarez 1946), and a third one (from La Cueva de Los Sabinos) was named Anoptichthys hubbsi (Alvarez 1947). Most if not all of the papers that still use either those names, or a combination of Astyanax and the specific names given to cave populations, are written by experimentalists, not field or taxonomic researchers. As more cave populations were discovered it became evident that this typological approach was creating a lot of confusion (Romero 2001).
Morphological Characteristics: Troglomorphic Characters: Troglomorphic individuals have reduced eyes (most are not externally visible), pigmentation (including totally depigmented), and a larger number of taste buds (Schemmel 1967). The surface and cave forms interbreed in both natural and laboratory conditions, producing fertile hybrids with a phenotypically intermediate form in the F₁ generation, and with an F₂ generation whose individuals range from an almost completely blind and depigmented form to an almost eyed and pigmented one (Peters and Peters 1973, Sadoglu 1957, Wilkens 1969). Breeding, electrophoretic, and karyotypic studies support the contention that the cave and epigean forms are the same species (Avise and Selander 1972, Kirby et al. 1977). Eye Condition: Reduced and usually not externally visible. Pigmentation: Reduced or absent pigmentation. Scales: Large and cycloid. Swim (gas) bladder:
Distribution: The epigean A. fasciatus is a freshwater fish with a broad distribution in the New World. Although obligatory and facultative cave populations of the eyed form have been reported for Belize and Costa Rica (Romero 1984), the Yucatán Peninsula (Hubbs 1938), and Brazil (Trajano 2001a), the only region in which they have developed into blind, depigmented individuals is the San Luis de Potosí Area, East Central Mexico, where at least thirty-one caves supporting subterranean populations of this fish can be found (Espinasa et al. 2001) (ca. 22^o 05' N, 99^o 00' W). Not all the cave populations of this area display the same degree of morphological divergence from the surface forms, however. Some are completely blind and depigmented while others are only partially so. Three caves contain only individuals with full eyes and pigmentation. Eleven of these populations include blind, eyed, as well as phenotypically intermediate forms (Mitchell et al 1977, Romero 1983, Espinasa et al. op. cit.).
Habitat and Ecology: In numerous caves. Some of those caves appear to be very poor from a trophic viewpoint while others (e.g., La Cueva Chica) have a very rich input of nutrients thanks to large bat colonies producing guano on which these fish feed.		Food and Feeding:
Reproduction and Development:		Other Behaviors: The two forms are not only different in their morphology, but also in their behavior: unlike the surface/ eyed form, the blind form never schools, is active all the time, and is not aggressive (Boucquey et al. 1965, Breder 1942, Breder and Gresser 1941, Erckens and Weber 1976). Although the blind form does produce an alarm substance, it does not respond to it (Pfeiffer 1966). Schemmel (1980) also reported differences between the two forms in the angle of inclination used when feeding from the bottom. Differences in the level of phototactic responses among different populations have also been reported (Romero 1985).
Conservation Status: Vulnerable. Major Threats:		Conservation Plans:
Phylogenetic Relationships: