Abstract
ABSTRACT Brycon orbignyanus is an endemic species from La Plata basin whose stocks have been presenting significant reductions throughout the Paraná River. Brycon orbignyanus is categorized as an endangered species. This study evaluated aspects of the bio-ecology of this species that may be related to this threat, highlighting its distribution, abundance, and diet as well as the corresponding relationships between its recruitment and flood regimes. Data were obtained from different parts of the upper Paraná River (stretches free and regulated by dams) from 1986 to 2010 with more detailed data collected from the free remnant of this basin. The results indicate that no records for species exist at more than half of the sampling points located in dam-regulated sections of the Paraná River, whereas specimens were collected from 75% sites in the free plain remnant. We observed a remarkable effect of the hydrological regime on recruitment as well as distinct food demands during ontogenetic development, with adults almost exclusively consuming fruits and seeds, revealing that these individuals are supported by riparian vegetation. Thus, it is concluded that changes in the natural flood regime as well as riparian vegetation removal threaten B. orbignyanus populations in the Paraná River basin.
Highlights
Riparian forest degradation is expected to negatively affect the piracanjuba’s diet, which largely consists of terrestrial food (Agostinho et al, 2008), while outflow dam control is a permanent threat to piracanjuba stocks since the reproduction and recruitment of this species depend on the occurrence of intense and prolonged flooding periods (Oliveira et al, 2015)
This study investigates piracanjuba’s (Brycon orbignyanus) biological and ecological features, which may be related to such threats, with an emphasis on species distributions, abundance, diet variations, and the relationship between recruitment and attributes of the hydrological regime
This study confirms that the piracanjuba has almost disappeared from upper Paraná River tributaries with reservoir cascades and that its presence in some of these areas may be attributable to stocking programs (CESP, 2000)
Summary
Brycon orbignyanus (Valenciennes, 1850), common name piracanjuba, is a species of reophilic and migratory fish exclusively found in the Paraná River basin and in Uruguay (Lima, 2017), playing an important role as a commercially exploited natural resource (Lima, 2017) before joining the IUCN list (Agostinho et al, 2008). Since the formation of the Porto Primavera reservoir at the end of 1998, flood attributes, such as their periods, intensity levels and durations, have been intensely altered (Agostinho et al, 2005). Under these conditions, an absence of regular flooding negatively affects the entire reproductive process of migratory species while the larvae of species that can reproduce under these conditions do not reach nearby lagoons, which serve as essential biotopes for growth and feeding in early development stages, due to a lack of connectivity between floodplain environments (Agostinho et al, 2005; Suzuki et al, 2009)
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