Influence of the Abaeté River on the reproductive success of the neotropical migratory teleostProchilodus argenteus in the São Francisco River, downstream from the Três Marias Dam, southeastern Brazil

Abstract

The curimatã-pacu Prochilodus argenteus is an important characiform from the São Francisco River basin that performs longdistance migrations for spawning upstream during the rainy season, when the temperature and photoperiod are elevated. Despite the interruption of the migratory routes by the Três Marias Dam and accentuated decline in fishing, the curimatã-pacu still sustains the fisheries at the Três Marias region in recent decades. The objective of this study was to evaluate the reproductive activity of P. argenteus in two sections of the São Francisco River, downstream from the Três Marias Dam, during the rainy season. In the first 34 km of the river, immediately below the dam, most of the females were in gonadal resting. At 34-54 km downstream from the dam, following the confluence with a medium-sized tributary, the Abaeté River, there was a high frequency of males and females in reproductive activity. Follicular atresia was more frequent in the upper section of the river while postovulatory follicles occurred predominantly in the lower section. Fulton's condition factor and gonadosomatic index indicated that the females were in a better physiological and reproductive condition below the confluence with the Abaeté River. In contrast to the females, the males were less affected by damming, and testicular maturation was largely achieved in two river sections. Thus, although the section of the São Francisco River immediately below the Três Marias Dam was found to be unfavourable for the reproduction of the migratory fishes due principally to the hypolimnetic water from the reservoir, reproductive success of P. argenteus was achieved below the Abaeté River. In this section, the species encountered appropriate conditions for maturation and spawning, i.e. warm temperatures above 24 C, high water flow and dissolved oxygen, and low water transparency. These results indicate the importance of a non-regulated tributary to minimize the ecological impact of a dam on the downstream native fish communities.

Blockage of migration routes by dam construction: can migratory fish find alternative routes?

“…This behavior is fundamental, since it can assure the reproduction and the perpetuation of populations even in situations in which principal migration routes are lost. Some recent studies have supported this trend, and reported that Prochilodus argenteus can successfully use tributaries downstream from Três Marias Dam (São Francisco River basin) for spawning (Sato et al, 2005;Godinho & Kynard, 2006). In addition, Godinho & Kynard (2006) also report the existence of different populations living in a short river stretch (~50km), using distinct migratory routes for spawning.…”

The roles of marginal lagoons in the maintenance of genetic diversity in the Brazilian migratory fishes Prochilodus argenteus and P. costatus

“…In fact, the existence of a single panmictic population for each species associated with the highly migratory behavior support the hypothesis of extensive gene flow among shoals. The convergence between rio São Francisco and rio Abaeté is considered the most important spawning site of Prochilodus argenteus (Godinho & Kynard, 2006), mainly because of the limnological conditions offered by the junction of the two rivers, such as water flow above 600 m³/ s, water temperature over 24ºC and concentrations of dissolved oxygen above 5 mg/l (Sato et al, 2005). As suggested by Hatanaka & Galetti (2003), one fraction completes its migration toward the dam during the reproductive period, and the majority possibly migrates to locations with environmental conditions more favorable for reproduction.…”

“…As suggested by Hatanaka & Galetti (2003), one fraction completes its migration toward the dam during the reproductive period, and the majority possibly migrates to locations with environmental conditions more favorable for reproduction. Sato et al (2005) (Sato et al, 2005).…”

Downstream impacts of a dam and influence of a tributary on the reproductive success of Leporinus reinhardti in São Francisco River

“…Changes in environmental conditions downstream from dams may negatively affect fish populations and their reproduction (Lessard & Hayes 2003, Sato et al 2005, mainly due to the de crease in temperature, which may cause a delay in spawning and embryo development and, hence, a reduction in the distribution of a species (Arantes et al 2010, Olden & Naiman 2010. The effects on fish populations downstream are not always negative.…”