Comparative analyses of reproductive activity inSchizodon knerii(Steindachner, 1875) (Characiformes: Anostomidae) in three sections of the São Francisco River basin

Abstract

Summary This paper aims to establish possible changes in the main reproductive parameters of the so‐called piau‐branco, Schizodon knerii, in three sections of the São Francisco River basin. Fish (n = 388) were captured quarterly between May 2012 and April 2013 from three sections of the São Francisco River (SFR): section 1 = Três Marias Reservoir (TMR), a lentic environment; section 2 = SFR, the first 34 km downstream of TMR, a lotic environment in which the temperature, oxygen levels, and flow are not suitable for reproduction; section 3 = SFR, 34–54 km downstream from TMR after the confluence with the Abaeté River, a lotic environment in which temperature, oxygen levels and flow are suitable for reproduction. In section 2, females and males showed lower values of total length and body weight in relation to fish from sections 1 and 3. The reproductive mode of S. knerii in sections 1 and 3 exhibited a prolonged reproductive period, parceled spawning, and a reproductive peak from January to March. In section 2, neither spawning females or spermiated males were captured, probably due to the fact that this section receives cold water with low oxygen levels from the hypolimium of the dam that presents thermal stratification in the summer. This study showed in section 2, immediately downstream of the Três Marias Reservoir, that S. knerii does not reproduce successfully.

The influence of a large reservoir on the reproductive activity of the white piranha, Serrasalmus brandtii (Lütken, 1875) in Southeast Brazil

“…Size at first gonadal maturation was determined as the smallest total length of females and males with gonads in the maturing/mature stage from each section (Boncompagni-Júnior et al 2013, Brandão et al 2017).…”

Morphological analysis of the reproductive activity of Curimatella lepidura (Characiformes: Curimatidae)

“…These species have pre‐adaptations to life in lentic environments and, in many cases, have great behavioural plasticity combined with low selectivity of habitat and resources, allowing them to complete their reproductive cycle in reservoirs (Agostinho et al, 2007). These factors may explain why fish caught in lotic environments, such as in sections 2 and 3 of this study, present relatively low‐reproductive performance that is similar to other species (Bazzoli et al, 2019; Brandão et al, 2017; Mantel & Hughes, 2010).…”

“…For histological analysis, the middle portion of the ovary and testis fragments of each fish, previously fixed in Bouin's liquid, were embedded in paraffin, cut at a 5 μm thickness, and stained with haematoxylin‐eosin. The frequency of gonadal maturation stages (GMEs) were established based on the macroscopic (entire gonads) and microscopic (gonad fragments) characteristics of the ovaries and testes, according to Brandão et al (2017). The type of spawning was determined based on the histological characteristics of spawned ovaries (Santos et al, 2004).…”

“…The size at first gonadal maturation was established based on the TL of the shortest female and male specimen found in the maturation/mature gonadal stage. This was done in accordance with the procedures used by Brandão et al (2017).…”

“…Immediately downstream of the Três Marias reservoir (TMR) (section 2), the water conditions of the São Francisco River (SFR) are not favourable for spawning of migratory fish species due to the release of hypolimnion water with temperatures below 24°C, constant flow, high transparency, and reduced dissolved oxygen levels (Sato et al, 2005). Hydrological and thermal alterations affect fish reproduction, including species that depend on lotic environments for spawning (Abdo et al, 2018; Brandão et al, 2017). Further downstream, after the confluence with a medium‐sized tributary (Abaéte River, section 3), the SFR has better conditions in terms of water temperature, dissolved oxygen, and flow rate, which favourably influence reproduction (Bazzoli et al, 2019; Nascimento et al, 2020).…”