Pterolebias longipinnis was described by Garman in 1895 has its locality type in the Amazon Basin, in the municipality of Santarém, Pará. He is a member of the Rachovini tribe (Costa, 1990), a including annual species endemic to the center and north of South America (Costa, 2014). The species has a great variation of color, mainly males, which are larger and more colorful than the females. The specimens photographed were all collected in a marginal pool on the Paraguay River, Pantanal plain (ZUFMS 5433, 5434). Identification. Three species of Pterolebias are described for South American drainage, two of which are found in Brazilian territory: P. longipinnis and P. phasianus Costa, 1988, while P. hoignei Thomerson, 1974 occurs only in the Orinoco basin in Venezuela. P. longipinnis has 3 to 4 scales in the anal sheath; dorsal with 9, pectoral with 15 to 16 and anal with 18-19 rays. Longitudinal line with 31 a 32 scales (Britski et al., 2007). The species presents marked sexual dimorphism. Beyond the colorful colorful that the males present in life, they have the ventral to the end of the anal and dorsal anal intercourse exceed the onset of flow while females have smaller fins and have a rounded edge. Biology. P. longipinnis is part of the fish group known as annual fish. This term refers to to a unique condition present in this group of fish, the diapausas. Diapauses are exclusive to a lineage of natural history of the Aplocheiloidei Americans and Africans (Parenti, 1981). There is no publication in the scientific field that addresses about its natural food supply but the from the mouth upwards, and the habit of living close to the water surface (Costa, 2005) suggest the capture of allochthonous items falling on the surface of the water, which is reinforced by observations in aquariums (obs. pess.). Field observations and collections in the Pantanal revealed that this species occurs in syntopy with the also annual P. phasianus and Trigonectes balzanii (Perugia, 1891) as well as several other species of non-annual fish, including in bays, non-temporal environments. Easily found and captured during the night while sleeping near the surface of the shallowest areas of wetlands. Distribution. The distribution of the genus Pterolebias covers the east and south of the Amazon basin and the Paraná-Paraguay, occurring in Brazil, Bolivia, Paraguay and Argentina. Within this geographical range, P. longipinnis is the most extensive species, occurring Marajó, in Pará, to Corrientes in Argentina (Costa, 2005). Conservation. Pterolebias longipinnis not found threat of extinction according to the recent list of threatened species (BRASIL, 2014). Thanks. To Tamires Yule and Matheus Volcan suggestions in the text and the Rufford Foundation for financial support (RSGF 22546-1). Literature cited. BRAZIL. 2014. National List of Brazilian Fauna Species Threatened Extinction. Available at: http: // www. icmbio.gov.br/portal/biodiversidade/ fauna-Brazilian / species-list.html. Access in [08/10/2017] Britski, H.A., Silimon, K. Z. S. & Lopes, B.S. 2007. Pantanal Fish: Manual of identification. Embrapa, Brasília, 230p. Costa, W. J. E. M. 1990. Phylogenetic analysis of the Rivulidae family (Cyprinodontiformes, Aplocheiloidei). Brazilian Journal and Biology, 50: 65-82. Costa, W. J. E. M. 2005. The Neotropical annual killifsh genus Pterolebias Garman (Teleostei: Cyprinodontiformes: Rivulidae): phylogenetic relationships, descriptive morphology, and taxonomic revision. Zootaxa, 1067: 1-36. Costa, W. J. E. M. 2014. Phylogeny and evolutionary radiation in seasonal rachovine killifishes: biogeographical and taxonomical implications. Vertebrate Zoology, 64: 177-192. Parenti, L. R. 1981. A phylogenetic and biogeographic analysis of cyprinodontiform fishes (Teleostei, Atherinomorpha). Bulletin of the American Museum of Natural History, 168: 335-557. __________ Federal University of Mato Grosso do Sul, Center for Biological of Health, University City, CEP 79070-700, Campo Grande, Mato Grosso of the South, Brazil. São Paulo State University "Júlio de Mesquita Filho" (UNESP), Institute of of Biosciences, Letters and Exact Sciences, Department of Zoology and Botany, Laboratory of Ichthyology, Rua Cristóvão Colombo, 2265, Jardim Nazareth, CEP 15054-000, São José do Rio Preto, SP, Brazil