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| (a, b) Psalidodon terezinhae (c, d) h P. velhochico (e, f) P. paiva Rodrigues-Oliveira, Assis, Pimente, Soares, Silva, Rocha, Menegidio, Pasa & Kavalco, 2025 |
Abstract
Psalidodon rivularis, a fish endemic to the São Francisco River Basin and known as “piaba do córrego,” has long been regarded as a widely distributed species complex, exhibiting remarkable morphological and cytogenetic variation, even in sympatry. This study aims to determine whether P. rivularis represents a single polymorphic species or a group of cryptic species. We analyzed meristic, morphometric, and karyotypic data from 419 specimens identified as P. rivularis, as well as from the related species Astyanax turmalinensis and Hyphessobrycon santae. Additionally, we inferred the phylogeny of the group using NGS data from 25 individuals, incorporating both mitochondrial and nuclear genomic sequences. Our integrative results support the recognition of at least five distinct species within the P. rivularis complex. The true P. rivularis (called morphotype 1) has 46 chromosomes, while the others have 50 and differ in both morphology and distribution. One of these corresponds to Psalidodon santae comb. nov.—which includes A. turmalinensis as a junior synonym—and three others are newly described species. These findings clarify the diversity of fishes in the São Francisco River Basin and highlight the importance of conserving its unique freshwater ecosystems.
Keywords: cytotypes; cryptic species; phylogenomics; morphometrics
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| Psalidodon terezinhae (a) holotype, LaGEEvo 27-4521, 53.0 mm SL, Lage stream, Abaeté River drainage and (b) LaGEEvo 35-529, 45.0 mm SL, Funchal River, Indaiá River drainage. P. velhochico (c) holotype, LaGEEvo 28-5079, 77.0 mm SL, Rasga Canga Waterfall, São Francisco River drainage and (d) LaGEEvo 51-4999, 75.0 mm SL, Casca d’Anta Waterfall, São Francisco River drainage. P. paiva (e) holotype, LaGEEvo 29-2072, 62.0 mm SL, Bonito stream, Borrachudo River drainage and (f) LaGEEvo 55, 34.5 mm SL, Usina do Abaeté dam Lagoon, Abaeté River drainage. |
Psalidodon terezinhae sp. nov.
Psalidodon velhochico sp. nov.
Etymology. The specific epithet velhochico is used as a noun in apposition and refers to the popular nickname of the São Francisco River in Brazil, affectionately called “Velho Chico” (“Old Chico”) by Brazilians.
Psalidodon paiva sp. nov.
Etymology. The specific epithet is used as a noun in apposition and honors the Paiva family, whose life, portrayed in the Brazilian Oscar-winning film “Ainda Estou Aqui” (2024), was profoundly affected by the imprisonment, disappearance, and execution of the family patriarch, Rubens Paiva, during the Brazilian military dictatorship.
Igor Henrique Rodrigues-Oliveira, Priscila Martins de Assis, Luiz Guilherme Pereira Pimente, Rafael Augusto Silva Soares, Iuri Batista da Silva, Renan Rodrigues Rocha, Fabiano Bezerra Menegidio, Rubens Pasa and Karine Frehner Kavalco. 2025. Unraveling a 150-Year-Old Enigma: Psalidodon rivularis (Acestrorhamphidae: Acestrorhampinae), a Species Complex or a Polymorphic Species. Biology. 14(12), 1793. DOI: doi.org/10.3390/biology14121793 [16 December 2025]
Simple Summary: This study investigates a group of closely related fish species from southeastern Brazil known as the Psalidodon rivularis complex. These fishes are very similar in appearance, which has made it difficult to know exactly how many species exist. By combining information from their body shape, body measurements, chromosome counts, and DNA, we found that what was once thought to be a single species includes at least five distinct ones. The true P. rivularis has 46 chromosomes, while the others have 50. One of them corresponds to Psalidodon santae, which was previously classified in another genus, and three are new species described here. Our results also suggest that their diversity arose through processes such as changes in chromosome numbers, hybridization between populations, and morphological divergence, potentially within broader scenarios that may involve vicariant or adaptive processes. These fishes live in small rivers and streams of the Upper São Francisco River basin, environments that are rich in unique species but threatened by human activities. Recognizing and protecting these new species is essential for conserving the biodiversity of Brazilian freshwater ecosystems.
