This very angient genus was described by the famous A. Valenciennes in 1839.

The genus name is derived from the greek mythological figure Orestes that said to have be hidden in the mountains. This connection was brought up as this genus was hidden in the mountains also and lived in high altitude Andian lakes in Peru and Bolivia.

The number of species whitin this genus is large but many species names are not valid and were synonymized by 3 major reviews based on morphological and data analizes. One by Eigenmann and Rosen in 1942, one by Tchernavin in 1944 and the last one by Parenti in 1984. All this knowledge was summarized by Wildekamp in 2004.

The author of this site is not specialized in this genus and the origin of all data, except the data from Killi Data Online, given here, are retrieved from the publication of Ruud Wildekamp's "A world of Killies" Vol: IV, 2004, a project sponsered by the American Killifish Association.

I like to thank Ruud Wildekamp for his cooperation and also tank the American Killifish Association for their support.

Literature

Valenciennes, A. 1839. Ichthyologie. Rapport sur quelques poissons de l'Amerique rapportés par M. Pentland du Lac Titicaca et des autres points éléves des Andes. L'Institut 7: 118

Comments herein...Source: Killi Data Online: Endemic genus with about 40 described species, of dwarf (3.5 cm) to very large size (27 cm), with strong polymorphism (most names are today thought to be synonyms); in Lake Titicaca, it may include only 4 to 6 distinctive species, the degree of interfertility being high: agassii highly variable, lutea, mulleri, cuvieri, pentlandii, gilsoni, and maybe ispi ; Parenti (1984a) considers 43 species as valid, however, this has been seriously challenged since Müller (1993), who points to mistakes and the use of non-quantitative criteria in Parenti's interpretation, and who suggests a much smaller number of valid species ; Villwock & Sienknecht (1995) report that sexual maturity is reached before the specimens reach their maximum size and that with further growth there are changes in body proportions, morphology, coloration, scalation and development of individual scales ; in addition, Mueller (1972) has shown that a parasitic infection by Metacercariae flatworm, a trematod, induces morphological and osteological modifications in specimens, notably head, and that it significantly affect Orestias morphology, and thus species determination ; consequently, on the basis of personal observations, published information, high interfertility, morpho-metric and osteological studies, and strong dimorphism along growth in most species (scale counts, body proportions), Villwock (pers. comm.) believes that many of the smaller Orestias agassii-like species can be regarded as synonymous with agassii and that within Lake Titicaca speciation is much more limited than anticipated and this view is accepted

since Huber (2000) and even extended by Wildekamp (2004) within a global synthesis of the genus, with a summary of all available knowledge, hence several described species turn into mere junior synonyms ; preliminary molecular studies by Lüssen et al. (2003, 2004) confirm this view and the non-correspondance of Parenti's morphological species with genetically distinct species.

Diagnosis: Very variable according to species variation (virus attacks) and within life span (dimorphism) according to development stages and because of occurrence of hybridization within and between complexes ; variable mouth, sometimes protractile; lack of Ventrals ; extended Dorsal and Anal in dominant male of some species; female, with a more rounded belly; distinct micromorphological characters such as reduced and irregular body squamation pattern and a unique head pore pattern (Parenti, 1981, 1984, Villwock 1986) ; 7 synapomorphies as a monophyletic group: (1) Ventral fins and fin girdle absent, (2) vomer absent, (3) middle Anal and middle Dorsal fin radials cartilaginous, rather than ossified, (4) bony anterior and posterior ceratohyal separated ventrally by a large gap filled with cartilage, (5) first postcleithrum absent; (6) anguloarticular without a ventral extension parallel to the retroarticular, (7) unique squamation and head pore pattern characterized by a prominent lyre-shaped arrangement of minute neuromasts and a prominent median dorsal ridge of scales running from top of head to Dorsal fin origin (Parenti, 1984a).

Phylogenetic positioning: relict, more related to Euro-Asian Aphanius than to Cyprinodontins of North America (molecular biology and osteology); the most primitive group of Cyprinodontins (osteology) ; the phylogenetic positioning of Orestias within Cyprinodontidae is today well documented (Villwock, 1963; Parenti, 1981; Parker & Kornfield, 1995; Costa, 1997), while in the old past it used to be related to Fundulidae and/or to the genus Empetrichthys, and more recently to Cynolebias, on the basis of frontal neuromasts patterns by Foster (1967) ; Protorestias Eigenmann & Allen (1942: 353, fig.) is a not defined name (derived from first, primary -from Greek: protos- Orestias, in reference to the theoretical ancestral position to Orestias) ; the name appears only in a figure showing a genealogy of Orestias species -today it would be termed as a phylogenetic tree- with at its base the name Protorestias in italics, as the ancestor of all reviewed species (a concept, not a real fish, i.e. exluded from the ICZN Code): if it were not written in italics and not with a Latin root («Pro» means ancestor), then there would be no rationale to consider it as a scientific name, even unavailable (Huber, 2006b) ; fully scaled species may be closely related to incompletely scaled species, as is the case with forgeti and ispi, which, along with pentlandii and cuvieri comprise the cuvieri complex, and in general (with exceptions), larger species tend to be irregularly scaled, whereas smaller species tend to be fully scaled (Parenti, 1984a).

In 2024 a new paper was released which states that the genus Orestias is not longer considered to belong to the family Cyprinodontidae. See below.

Morales, P., Gajardo, F., Valdivieso, C. et al. Genomes of the Orestias pupfish from the Andean Altiplano shed light on their evolutionary history and phylogenetic relationships within Cyprinodontiformes. BMC Genomics 25, 614 (2024).

https://doi.org/10.1186/s12864-024-10416-w

Oor check this link to the paper:

https://rdcu.be/dOnkA

The evolutionary history of the Orestias genus is linked to the South American ichthyofauna and it should no longer be considered a member of the Cyprinodontidae family. Instead, we submit that Orestias belongs to the Orestiidae family, as suggested by Freyhof et al. (2017), and that it is the sister group of the Fluviphylacidae family, distributed in the Amazonian and Orinoco basins. These two groups likely diverged during the Late Eocene concomitant with hydrogeological changes in the South American landscape.