Brycon opalinus ( Cuvier, 1819 )

Rodrigues, Leydiane Nunes, Silva, Juliana Paulo Da, Lima, Flávio César Thadeo, Ingenito, Leonardo Ferreira Da Silva, Duboc, Luiz Fernando, Machado, Débora Ferreira & Sarmento-Soares, Luisa Maria, 2021, The genus Brycon Müller & Troschel (Ostariophysi: Characiformes: Bryconidae) of Espírito Santo State, Brazil: new records and comments on conservation, Zootaxa 5072 (2), pp. 145-156 : 150

Brycon opalinus ( Cuvier, 1819)

Local name. Pirapitinga.

Distribution and additional records. Brycon opalinus was previously known from the upper rio Paraíba do Sul and upper rio Doce basins in the states of São Paulo, Rio de Janeiro, and Minas Gerais, Brazil ( Lima 2017). Its current geographical range is highly fragmented and restricted to some headwater tributaries of the rio Paraíba do Sul and rio Doce basins, with relatively healthy populations in some river stretches ( Lima 2017). There is an old record for the species downstream from the rio Doce in Espírito Santo State, considered doubtful by Lima (2017) in view of the known preference of the species for headwater areas. Brycon opalinus is recorded herein for the first time from the rio Itapemirim ( figure 5 ), a river system located in the southern portion of the Espírito Santo State. The specimens were all sampled in the upper rio Itapemirim basin, in the rio Braço Norte Direito, on a stretch limited upstream by Parque Estadual da Cachoeira da Fumaça (PECF) and downstream by Central Geradora Hidrelétrica (CGH) Francisco Gross, near the mouth of tributaries.

Habitat and ecological notes. Brycon opalinus is found in headwater areas, inhabiting small rivers, characterized by possessing slightly dark-stained to clear waters, and lentic stretches alternated with rapids ( Lima 2017). All B. opalinus specimens collected in the rio Itapemirim basin were found in stretches close to rapids. The rio Braço Norte Direito near Parque Estadual da Cachoeira da Fumaça , where the species was first recorded in this basin in the years 2012 and 2013, had a maximum width of 28.6 m, a maximum depth of about 2.2 m, and the river in this stretch has a fast current with rapids. The substrate is composed mainly of sand and pebbles, with scattered rocks. Water transparency in this river varies markedly throughout the year, with relatively low turbidity and clear waters during the dry season, and turbid waters, with low transparency, during the rainy season. The catchment area of the rio Braço Norte Direito is mostly deforested, being mainly composed of pastureland, with a few more vegetated areas in an initial phase of succession.

Brycon opalinus is not known to undertake large migrations ( Lima 2017). It is likely that this species uses the rio Braço Norte Direito as a migratory corridor and spawning area (this river stretch is approximately 18 km long). This assumption is based on the fact that only juveniles were recorded within the Parque Estadual da Cachoeira da Fumaça (PECF) ( Rodrigues 2013), which is situated downstream from a waterfall 144 meters high, which corresponds to a natural barrier for most of the aquatic fauna in this river. The PECF protects a preserved section of rio Braço Norte Direito, one of the main tributaries forming the rio Itapemirim. While the few recorded adult specimens were found downstream from the PECF, in the area comprised by CGH Francisco Gross.

Figures

FIGURE 5. Brycon opalinus, MBML 9587, 145.9 mm SL: Brazil, Espírito Santo, rio Itapemirim basin.