Flow-dependent fish specialists require specific conditions for reproduction, so the success and reproductive intensity of these animals are determined by the flood regime. Thus, this study investigated the spatial and temporal reproductive patterns of fish, especially migratory Prochilodus species (flow-dependent specialists) in an unusual period of low flow in the Pará River sub-basin, one of the main tributaries of the upper São Francisco River. For this, ichthyoplankton collections were carried out between November 2013 and February 2014. Data were analysed considering the spatial and temporal variations in density of eggs and larvae for the upper, middle, and lower portions of the Pará River sub-basin, and correlating this to some environmental variables. The results showed that the small headwater stretch of the Pará River is one relevant spawning area for migratory fish species. However, this area is isolated by the Cajuru reservoir, which makes it uncertain the recruitment of these embryos, due to interruption of natural drift between spawning/nursery areas caused for reservoirs.Larvae of newly hatched migratory species found in tributaries of the lower Pará River sub-basin also indicate these species use these tributaries as spawning grounds and migratory routes. The period in which the research was conducted represented the most atypical low flow, one in the last 75 years, resulting in the low variability in the environmental parameters. Although few parameters increased briefly in this low flow period influenced by greater rainfall in December, this precipitation was possibly responsible for the final gonadal maturation and spawning of migratory species.

No abstract

The introduction of invasive species is a significant threat to freshwater ecosystems and is changing the biogeographic patterns of fish species, leading to homogenization of fish fauna. The ability to predict potential invasions is critical in conservation biology to avoid further biodiversity loss. Ecological niche modelling has become an important tool in biological invasion studies. However, some introduced species can spread to habitats that are different from those in their native range. A framework based on niche shifts and ecological niche models was used to show that Pterygoplichthys ambrosettii, an armoured catfish, commonly known as ‘pleco', and native to the middle‐lower Paraná river, has expanded its niche by 27% and is now occupying a new range of environmental conditions. This species has experienced a niche shift from its original habitat and has started to occupy new areas of the Upper Paraná river basin and the São Francisco basin in Brazil. Models built using both native and non‐native areas were not able to predict the invaded habitats, and in either the native or non‐native areas the cross‐validation procedures corroborate the niche expansion hypothesis.

The study of ichthyoplankton composition, abundance and distribution is paramount to understand the reproductive dynamics of local fish assemblages. The analysis of these parameters allows the identification of spawning sites, nursery areas and migration routes. However, due to the lack of characters in early life stages, the morphological identification of ichthyoplankton is often impractical and many studies identify only fish larvae. Additionally, its accuracy shows great variation between taxonomists and laboratories according to their experience and specialty. DNA barcoding emerged as an alternative to provide assertive identification of fish eggs and larvae, but it becomes too expensive and laborious when the study demands the processing of huge amounts of organisms. DNA metabarcoding can overcome these limitations as a rapid, cost-effective, broad and accurate taxonomy tool, allowing the identification of multiple individuals simultaneously. Here, we present the identification of a sample containing 68 fish eggs and another containing 293 fish larvae from a single site in the São Francisco River Basin, Eastern Brazil, through DNA metabarcoding. We used a low-cost saline DNA extraction followed by PCR amplification with three primer sets targeting the 12S rRNA gene: MiFish (~170bp), Teleo_1 (~60bp), and NeoFish (~190bp). The latter was recently developed by our research group specifically for the identification of Neotropical fishes. All the amplified samples were sequenced in a single multiplexed Illumina MiniSeq run. We performed the filtering steps and assigned Amplicon Sequence Variants (ASVs) using a DADA2/Phyloseq based pipeline and a custom 12S reference sequence database including 101 species and 70 genera from the Jequitinhonha and São Francisco basins. The species Cyphocharax gilbert, Leporinus taeniatus, Megaleporinus elongatus, Prochilodus argenteus, P. costatus and Psalidodon fasciatus were detected by all three primer sets in the larva pool, while Pterygoplichthys etentaculatus was detected solely by NeoFish (Fig. 1). Within the egg pool, all three markers detected the species Characidium zebra, Curimatella lepidura, M. elongatus, Pimelodus fur and P. costatus, but Brycon orthotaenia was detected only by NeoFish, P. maculatus only by Teleo, and P. pohli by MiFish and Teleo (Fig. 1). The consistency in species detection among all three markers underpins the credibility of this method to accurately describe the sample composition. Considering that most of species were exclusive to the larvae or egg pool, our experiment highlights the importance of including the identification of fish eggs in reproduction studies, as it can provide additional information about which species are spawning in an area. Furthermore, the application of DNA metabarcoding to the study of ichthyoplankton can help decision makers create more informed guidelines for conservation of economically and ecologically important fish species.

We established the length–weight relationships (LWR) for 78 fish species from the São Francisco River basin, Brazil. Samples were originated from different scientific projects performed between 1993 and 2019. Fishing gears used were mainly gillnets and cast nets of various mesh sizes. Specimens varied from 0.6 to 128 cm (18.1 ± 11.8 cm) and from 0.01 to 26,900 g (317.9 ± 733.6 g). The allometric coefficient b varied from 2.509 to 3.494. For 66 species, the LWR parameters were completely novel and, for the other 12 species, are present for the first time for the São Francisco River basin.

Abstract:Megalancistrus barrae is a species endemic to the São Francisco River basin that has not previously been recorded from the Upper São Francisco basin.The present work increases the known distribution of the species by reporting new collections from two different regions in the Upper São Francisco basin: one in the Pará River and the other in the São Francisco River, downstream Três Marias dam, Minas Gerais state. In addition, this study compiles distributional data on Megalancistrus barrae from museums.

The ichthyofauna of the Rio São Francisco basin is relatively well-documented. However, most of this knowledge is concentrated at the upper stretch of its catchment area. In this study, we compile a list of species encompassing almost the entire length of the Rio Carinhanha, an important tributary from upper-middle section of the Rio São Francisco, including a comprehensive diversity of environments. A total of 99 species from 8 orders and 27 families were recorded. Five species are considered non-native, six classifieds as long distance migrants, and three as vulnerable. The orders with the greatest richness of native species were Characiformes and Siluriformes. Characidae was the most represented family, followed by Loricariidae. The main river channels were the richest environments sampled, followed by floodplain lagoons, veredas, and streams. The Carinhanha basin has important lotic remnants, thus it has several migratory fish populations as well as endangered species. This study demonstrates the importance of cataloguing the still poorly explored tributaries of the upper-middle section of the Rio São Francisco basin.

No abstract