Reproductive aspects of piranhas Serrasalmus spilopleura and Serrasalmus marginatus into the Upper Paraná River, Brazil

Abstract

Construction of the Itaipu Dam, 150 km downstream from Sete Quedas Falls, resulted in the drowning of that natural geographic barrier, with consequent invasion of Serrasalmus marginatus in the upper stream. This event was followed by the reduction in the abundance of the native species, S. spilopleura. Analyzes of reproductive activity these species revealed that in lotic waters S. marginatus had a very intense reproductive activity while activity of S. spilopleura was nil. This, probably made it possible for the invading species to occupy new environments into the Upper Paraná River, using the river as an entry port. In the 1987-1988 period there was a marked decline in reproductive activity of S. spilopleura reflecting the negative effects of its interaction with the invading species, S. marginatus. The assertiveness of S. marginatus in caring for its offspring and aggressiveness in establishing its feeding territory may be the determining factor for its competitive superiority over S. spilopleura, and consequently its success in colonizing the Upper Paraná River. In addition to the negative interference of S. marginatus, a possible recruitment failure of S. spilopleura could have benefited the colonization of the floodplain by the invader species.

<b>Endoparasitic fauna of <i>Serrasalmus</i> spp. (Characidae: Serrasalminae) in a neotropical floodplain

“…Crustaceans are, in general, intermediate hosts for some Echinorhynchus (Acanthocephala) species and, because of this, crustaceans can carry larval forms of these parasites (Schmidt, 1985). As S. marginatus presents territoriality and aggression in its behavior (Agostinho, 2003), this allows a better foraging for this species and consequently a large amount of acanthocephalans. So, S. marginatus ingests a greater number of infected intermediate hosts than S. maculatus and consequently a large amount of acanthocephalans larvae.…”

“…According to Agostinho (2003), in a study about those species condition factor variation pattern in the Paraná river floodplain, it indicated that the most important is food availability and not reproductive events, since in food shortages periods have shown reduced condition factor, especially in immature individuals. Besides, it can be assumed that males and females have similar diets, what did not influence these fishes parasitism.…”

“…Agostinho, Julio Júnior, and Petrere Júnior (1994) since the Itaipu reservoir construction, which caused the two population fauna mixing. Because of this process, S. marginatus achieved large population growing in the new habitat, demonstrated by the increasing number of specimens collected (Agostinho, 2003).…”

<b>Ovarian histology and fecundity in the evaluation of the reproduction of the invasive species <i>Serrasalmus marginatus</i> (Characidae) on a neotropical floodplain

“…These rivers belong to the upper Paraná River floodplain and are two of the main tributaries responsible for the maintenance of ichthyofaunistic diversity and serve as nursery and growth areas, mainly for migratory species (Agostinho, Thomaz, Minte-Vera, & Winemiller, 2000; Reynalte-Tataje, Agostinho, & Bialetzki, 2013). Therefore, these sites are characterized by possessing adequate conditions for the establishment of S. marginatus and, consequently, the population increase of this species results in negative impacts for the native species S. maculatus, as the two are congeners that have similar environmental and feeding requirements (Agostinho & Júlio Jr, 2002;Agostinho, 2003;Alexandre, Luiz, Piana, Gomes, & Agostinho, 2004).…”

“…The reproductive success of S. marginatus on the upper Paraná River floodplain is attributed to parental care and greater aggressiveness in defending its feeding and reproduction territories (Agostinho, 2003;Alexandre et al, 2004). However, it is also associated with fecundity, because the long reproductive period with the continual spawning of oocytes guarantees more descendants.…”