Spatial and temporal distribution of ichthyoplankton during an unusual period of low flow in a tributary of the São Francisco River, Brazil

Abstract

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.

Dispersal of fish eggs and larvae in a cascade of small hydropower plants with fish ladders

“…Similarly, successful drift and downstream passage of eggs and larvae have been reported at other hydropower plants with comparable characteristics (Suzuki et al, 2011;Fuentes et al, 2016). A fundamental condition to maintain the dispersal process is high water discharge and low water retention time (Rosa et al, 2018). Indeed, this has also been noticed for the study area where, at certain sampling periods coinciding with lower flows and higher water retention time both dams had the lowest eggs and larvae densities.…”

Arms as areas for larval development of migratory fish species in a Neotropical reservoir and the influence of rainfall over abundances

“…The coincidence of greater larval densities with periods of greater rainfall suggests that populations of migratory species respond to the same environmental stimuli to reproduction as conspecifics in nondammed environments. The reproduction of migratory fish is directly linked to the hydrological cycle (Agostinho et al, 2004;Harvey & Carolsfeld, 2003;Lozano et al, 2019;Rosa et al, 2018;Vazzoler, 1996), with the rainfall regime described as a trigger for the reproduction of tropical fish (Lopes et al, 2018;. Rainfall can affect a variety of hydrologic factors, including flow, transparency, electrical conductivity and fluviometric level, which are directly related to spawning (Baumgartner et al, 2008;Vazzoler, 1996) and to the transport and survival of ichthyoplankton and recruitment (Baumgartner Despite the damming limiting the influences of flow velocity and fluviometric level, rainfall apparently influences the onset of migration to free stretches of the tributaries, where the species spawn (Marques et al, 2018).…”

Genetic evaluation of migratory fish: Implications for conservation and stocking programs

“…Surprisingly, fish sampled at the Paraopeba River site were the only ones with gene pool 4, which was present at high frequency (>90%). Environmental factors can trigger spawning seasons that affect recruitment area selection (Rosa et al, 2017), and likely have changed allele frequencies at the population level (see more details in Appendix ).…”

“…If the allele with the largest number of reads does not exceed 80%, we consider the second allele, and if it encompasses ≥20% of the total reads, we consider the individual to be heterozygous. Rosa, Salvador, Bialetzki, & Santos, 2017; https://doi.org/10.1007/s00335-016-9670-7) established a minimum of two reads to confirm the less frequent allele. In our work, we set the minimum depth at 10 reads, 20% of which would give at least two reads confirming the less frequent allele.…”