Simpsonichthys de Carvalho

Wilson J. E. M. Costa, 2007, Taxonomic revision of the seasonal South American killifish genus Simpsonichthys (Teleostei: Cyprinodontiformes: Aplocheiloidei: Rivulidae)., Zootaxa 1669, pp. 1-134 : 5-6

[[ Genus Simpsonichthys de Carvalho ]]

The genus Simpsonichthys Carvalho is the most speciose and geographically widespread genus of neotropical seasonal rivulids. It occurs over a vast region of South America, including the Jaguaribe, São Francisco, Pardo, Jequitinhonha and Doce river basins and smaller isolated river basins of northeastern, eastern and southwestern Brazil; southern tributaries of the Amazon River basin, including the Tocantins, Araguaia, and Xingu drainages in Brazil; the Mamoré River basin in Bolivia; the Paraguay River basin in Paraguay and Bolivia; and the upper Paraná River basin in central Brazil (Costa, 1996, 2006a). All species of Simpsonichthys spend their entire lives in shallow seasonal pools formed by rains, in different natural areas of South America (Costa, 1995), including rainforests (the Amazonian forest and the Atlantic forest, including the adjacent coastal Restinga); semiarid areas (the Caatinga of northeastern Brazil, the Gran Chaco of Paraguay and Bolivia, and a coastal area of Rio de Janeiro state, southeastern Brazil); and savanna-like regions such as the Brazilian Cerrado, which includes forested vegetation formations such as the Mata Ciliar and Mata de Galeria, and open vegetation formations as Campo Limpo, Brejos, and Buritizal (Buriti-palm). The pools in all these regions are dry during some months of the year (usually between July and November), when all individuals die. Embryos, protected by the thickened outer layer of egg, undergo a diapause until the beginning of the rainy season (which usually lasts from November to March).

Simpsonichthys comprises a genus of small to median sized killifish species, usually reaching 35 to 60 mm standard length as adults, although one species, S. ghisolfii Costa, Cyrino & Nielsen, is known to reach about 75 mm SL. At the opposite extreme, S. parallelus Costa, S. nigromaculatus Costa, S. cholopteryx Costa, Moreira & Lima, S. costai (Lazara), S. reticulatus Costa & Nielsen, and S. semiocellatus (Costa & Nielsen) are miniature species not exceeding 26 mm SL. A remarkable feature of species of Simpsonichthys is the strong sexual dimorphism, the males possessing striking color patterns and longer fins than females. Meristic differences between sexes of the same species are common, especially with regard to numbers of dorsal and anal rays (counts in males are always greater). In addition, the dorsal and anal fins of males often have filamentous rays. Because of their small size, beauty, and diversity of color patterns and fin morphology, species are widespread in the aquarium trade, often appearing in aquarium magazines and on internet sites throughout the world. Several species are maintained by specialized breeders and have become popular aquarium fishes.

Despite their vast geographic range and great morphological diversity, it is surprising that all known 50 species of Simpsonichthys were described after 1941, and 46 of these have only been described within the last 20 years. This is a consequence of recently increased interest in South American seasonal fishes, which has resulted in greater collecting effort and an increased number of publications involving the ecology and taxonomy of these fishes. This work has also revealed, unfortunately, that several species are threatened with extinction (Costa, 2002).

Species of Simpsonichthys have been the focus of recent phylogenetic studies (Costa, 1996, 1998, 2003, 2006a). Despite this work, some species are still poorly known, and data on morphology and geographic distribution is often limited to that appearing in their original descriptions. The present revision incorporates a considerable amount of new information; including detailed descriptions of species, primary synonyms, taxonomic keys to subgenera and species, lists of material examined, and information on geographic distribution and habitat for each species.