First record of a bird in the stomach contents of Serrasalmus maculatus (Kner, 1858) in the Upper Paraná Basin

Primeiro registro de uma ave no conteúdo estomacal de Serrasalmus maculatus (Kner, 1858) na Bacia do Alto Paraná

Abstract

This article reports the first recorded occurrence of a bird in the stomach contents of Serrasalmus maculatus (Kner, 1858) in a reservoir environment in the Ipanema National Forest, São Paulo, Brazil, Upper Paraná River basin. The specimen, a mature female measuring 19.7 cm standard length, contained 12.6 mm³ of Nannopterum brasilianum feathers and 6.48 mm³ of fish fragments in its stomach. Local environmental conditions, slightly alkaline water, muddy substrate, and dense marginal vegetation, promote strong connectivity between aquatic and terrestrial habitats, creating opportunities for occasional trophic interactions. This record highlights the opportunistic feeding behavior of the species and expands knowledge of its trophic ecology in lentic environments.

Keywords
Diet; food plasticity; allochthonous vertebrates; Serrasalmidae; trophic ecology

Resumo

Esse artigo relata o primeiro registro de ocorrência de ave no conteúdo estomacal de Serrasalmus maculatus (Kner, 1858), em ambiente represado na Floresta Nacional de Ipanema, São Paulo, Brasil, Bacia do Alto Rio Paraná. O exemplar, uma fêmea madura com 19,7 cm de comprimento padrão, apresentou 12,6 mm³ de penas de Nannopterum brasilianum e 6,48 mm³ de fragmentos de peixe em seu conteúdo estomacal. As condições ambientais locais, água levemente alcalina, substrato lodoso e vegetação marginal densa, favorecem elevada conectividade entre os ambientes aquático e terrestre, criando oportunidades para interações tróficas ocasionais. O registro evidencia o comportamento alimentar oportunista da espécie e amplia o conhecimento sobre sua ecologia trófica em ambientes lênticos.

Palavras-chave
Dieta; plasticidade alimentar; vertebrados alóctones; Serrasalmidae; ecologia trófica

Introduction

Serrasalmus maculatus (Kner 1858) is the only native serrasalmid in the Sorocaba River Basin (Costa et al. 2005; Smith et al. 2007). It belongs to the Neotropical family Serrasalmidae, which includes 101 species and 16 genera (Favarato 2019; Mastrochirico-Filho et al. 2021), with piranhas accounting for about half of these species (Géry 1984; Andrade et al. 2019; Moraes et al. 2023). S. maculatus, revised from S. spilopleura by Jégu (2003), is notable as the basin’s sole species.

Piranhas, or pirambebas, are social fish that can form groups of three to 20 individuals and attack their prey when they are distracted, disoriented, or vulnerable. They are primarily active during the day and extend their foraging time into the early evening because they feed visually (Sazima and Pombal Junior, 1988; Villares Junior et al., 2008). They are capable of tearing chunks from their prey with their sharp teeth and can attack considerably larger animals. They are primarily carnivorous and employ a highly opportunistic feeding strategy (Britski et al. 1984; Gomes & Verani 2003; Behr & Signor 2008; Villares Junior et al. 2008). The species is characterized by a strongly compressed body, generally tall, possessing a single set of teeth in both jaws and a serrated keel on the chest, formed by scales modified into spines (Machado-Allison & Garcia 1986; Raposo & Gurgel 2003). Due to their morphological characteristics, they are fish characteristic of lentic environments and are commonly caught in backwater areas (Agostinho & Julio Junior 2002; Behr & Signor 2008). In these environments, aquatic macrophyte beds play an important role for the species, functioning as shelter areas against predators, foraging sites, and also potential sites for reproduction and initial development of juveniles (Agostinho et al. 2003; Oliveira et al. 2020). Aquatic vegetation increases habitat structural complexity, favoring territorial behavior, egg deposition, and offspring protection, characteristics frequently reported for serrasalmids in floodplains and vegetated marginal environments (Sánchez-Botero & Araújo-Lima 2001).

Understanding the diet of this species is key to assessing its ecological interactions (Hahn et al. 1997). This study examines dietary habits and their ecological implications for S. maculatus. Dietary analysis enables evaluation of predation, competition, and trophic relationships, revealing core aspects of ichthyofauna feeding ecology (Costello 1990). Neotropical fish like S. maculatus have flexible diets, adjusting food sources to spatiotemporal environmental changes (Abelha et al. 2001). Feeding activity generally increases during flood periods - when the specimen was collected - due to increased availability of allochthonous items from bank flooding (Goulding 1980; Rodrigues 2013) and more preserved riparian vegetation (Barili et al. 2011; Vaz et al. 2018). In the dry season, lower water levels limit access to marginal resources and reduce prey, leading to broader dietary choices and opportunistic feeding (Pereira et al. 2004). Thus, the record of bird consumption likely reflects an opportunistic event, linked to reduced aquatic resources and higher organism concentrations in the channel during low flow, which favored the ingestion of atypical prey.

Within this context, previous studies have already recorded opportunistic feeding behaviors in piranhas, including the ingestion of vertebrates during periods of high water (Winemiller 1989; Andrade et al. 2019). Behr & Signor (2008) recorded the occurrence of birds in S. maculatus in the Uruguay River. However, until now, no records had been found for the Upper Paraná. Thus, in this brief communication, we present the feeding record of Nannopterum brasilianum in the stomach contents of a specimen of S. maculatus collected at the Hedberg Reservoir, located in the Ipanema National Forest.

Material and Methods

This study was conducted at the Hedberg Reservoir (Figure 1), located on the Ipanema River, a tributary of the Sorocaba River, within a Conservation Unit (CU). The Ipanema National Forest (FLONA de Ipanema) covers 5,180 hectares and is located between the municipalities of Iperó, Capela do Alto, and Araçoiaba da Serra (Smith et al., 2021). Data collection took place in November 2023 using 10 m long, 1.5 m high gillnets with 10 cm mesh between opposite nodes. The nets remained at the sampling point for 12 hours, being placed at dusk and retrieved at dawn the following day. The collections were carried out with authorization under the permanent licenses for the collection of zoological material nº 24151-1 and 85747-1 (Authorization and Information System in Biodiversity – SISBIO) and the certificate from the Ethics Committee on the Use of Animals (CEUA nº 4721030821) of Paulista University (UNIP).

Figure 1
Location of the Ipanema National Forest, Iperó, Brazil, together with the Hedberg Dam and the collection point for the Serrasalmus maculatus specimen.

After collection, the individual was measured to determine standard length and total weight, and then anesthetized with clove oil and immersed in ice. The specimen was taxonomically identified, and key specimens were deposited in the fish collection of the Museum of Biological Diversity of the State University of Campinas – UNICAMP (ZUEC 18332 and ZUEC 18334), being identified by the systematist Flávio C. T. Lima.

For the evaluated stretch, environmental variables were measured; three types of chemical variables were collected using an Oakton PCD650 series multiparameter probe (pH, conductivity (µs), and total dissolved solids (ppm)), and environmental characterization of the sampling point was performed.

In the Laboratory of Structural and Functional Ecology of Ecosystems, located at Paulista University, Sorocaba campus, the dissection of the individual and the removal of the stomach were performed with the aid of scissors, forceps, and scalpels. An incision was made starting at the anal opening and ending near the pectoral fins. The stomach contents were analyzed under a stereomicroscope, with the identified items separated into Petri dishes. Immediately afterward, the stomach was placed in a test tube containing 70% alcohol.

The dietary item was quantified using the volumetric method (Vi), in which the food item’s volume was measured in test tubes and a glass counting plate (Hellawell & Abel 1971). Food items were identified to the lowest possible taxonomic level using taxonomic keys.

Results and Discussion

The collection point for the Serrasalmus maculatus specimen is located near the northwest bank of the Hedberg Dam reservoir (23°25′37.44′′S, 47°35′50.13′′W), in the Ipanema National Forest (Figure 2). The environmental characterization of the collection point reveals a typically lentic environment, with a slightly alkaline pH (7.6), low conductivity (120 µS cm⁻¹), and reduced total dissolved solids concentration (66.7 ppm), conditions indicative of good water quality and low direct anthropogenic influence. The muddy substrate and accumulation of organic matter, combined with the presence of aquatic macrophytes and marginal vegetation composed of grasses, shrubs, and small trees, create a habitat with high structural heterogeneity, which is highly compatible with the ecological preferences of the species (Sazima & Machado 1990; Hoffmann et al. 2005), in addition to providing nesting and foraging sites for aquatic and semi-aquatic birds.

Figure 2
Hedberg Dam in the Ipanema National Forest, Iperó, Brazil. A, Dam located between the Ipanema River and the Hedberg Dam; B, Hedberg Dam; C, Sampling point on the banks of the Hedberg Dam.

The specimen analyzed (Figure 3), a mature female measuring 19.7 cm in standard length and weighing 317.38 g, presented a total stomach content of 19.08 mm³, composed of 6.48 mm³ of fish fragments and 12.6 mm³ of bird feathers. The presence of this material in a volume greater than that of piscivorous material indicates an opportunistic feeding event, where the bird was possibly deceased. This is supported by the fact that during flood periods, water levels approach the vegetated banks, increasing the availability of allochthonous prey (Barili et al. 2011; Rodrigues 2013).

Figure 3
Serrasalmus maculatus, 197 mm SLW, 317.38 g, female; collected in the Ipanema River, Sorocaba River basin, Iperó municipality (SP - Brazil); 23°25′37.44′′S 47°35′50.13′′W. Photo: Welber Senteio Smith.

The marginal vegetation in the reservoir harbors several bird species, many of which are diurnal and coincide with the peak foraging period of S. maculatus (Villares Junior et al. 2008). This temporal and spatial overlap favors occasional interactions between predators and potential allochthonous prey. Thus, the record of feathers in the stomach contents (Figure 4) suggests a direct predation event or opportunistic scavenging, a behavior already described for piranhas in other contexts (Winemiller 1989; Andrade et al. 2019), but unprecedented for the Upper Paraná Basin.

Figure 4
Stomach contents and histology of Serrasalmus maculatus. A, histology of mature female magnified 10x; B, stomach contents analyzed; C, slide containing the feather of Nannopterum brasilianum located in the stomach.

Previous studies on the species’ diet indicate a predominantly piscivorous diet, with the ingestion of fish muscle tissue, scales, and fins (Behr & Signor 2008; Miguel et al. 2022). However, the trophic plasticity of S. maculatus allows it to occasionally consume terrestrial or allochthonous vertebrates, reinforcing its ability to exploit resources as they become available (Hahn et al. 1997; Abelha et al. 2001). This flexibility can be advantageous in dammed systems, where the community structure and prey supply vary seasonally.

The recorded occurrence also highlights the importance of marginal reservoir environments within Conservation Units. Even in protected areas, hydrological alterations resulting from damming modify the lateral connectivity pattern, favoring the access of aquatic predators to new food sources (Pereira et al. 2016). Thus, the presence of a bird in the stomach contents of S. maculatus may reflect not only the species’ opportunistic feeding habits but also the ecological role of dams in amplifying unexpected trophic interactions. In summary, this study represents the first record of a bird in the stomach contents of S. maculatus in the Upper Paraná Basin and reinforces the opportunistic and generalist nature of its diet, expanding knowledge of the species’ feeding ecology.

• Ethics
  Not applicable.

Acknowledgments

The authors would like to thank the Chico Mendes Institute (ICMBio) for the sampling licenses and the Vice-Rector for Postgraduate Studies and Research at Universidade Paulista (UNIP) and the Laboratory of Structural and Functional Ecology of Ecosystems at Universidade Paulista for logistical support. To Luis Gustavo Nogueira de Carvalho for preparing the map. The CAPES Process 88887.114010/2025-00 scholarships were awarded to the first author. CNPq Process 132189/2025-9 scholarships were awarded to the third author. Toyota Brasil granted the fourth author a research grant, in addition to the support and logistical assistance.

Data Availability

All data are available in the paper.

References

• ABELHA, M.C.F., AGOSTINHO, A.A., & GOULART, E. (2001). Plasticidade trófica em peixes de água doce. Acta Scientiarum: Biological Sciences, 23(2), 425–434. https://doi.org/10.4025/actascibiolsci.v23i0.2696
  » https://doi.org/10.4025/actascibiolsci.v23i0.2696
• AGOSTINHO, A.A., GOMES, L.C., & JULIO JUNIOR, H.F. (2003). Relações entre macrófitas aquáticas e fauna de peixes. In S. M. Thomaz, & L. M. Bini (Eds.), Ecologia e Manejo de Macrófitas Aquáticas (pp. 261–279). Editora da Universidade Estadual de Maringá.
• AGOSTINHO, C.S., & JULIO JUNIOR, H.F. (2002). Observation of an invasion of the piranha Serrasalmus marginatus Valenciennes, 1847 (Osteichthyes, Serrasalmidae) into the Upper Paraná River, Brazil. Acta Scientiarum: Biological Sciences, 24(2), 391–395.
• ANDRADE, M.C., WINEMILLER, K.O., BARBOSA, P.S., FORTUNATI, A., CHELAZZI, D., CINCINELLI, A., & GIARRIZZO, T. (2019). First account of plastic pollution impacting freshwater fishes in the Amazon: Ingestion of plastic debris by piranhas and other serrasalmids with diverse feeding habits. Environmental Pollution, 244, 766–773. https://dx.doi.org/10.1016/j.envpol.2018.10.088
  » https://doi.org/10.1016/j.envpol.2018.10.088
• BARILI, E., AGOSTINHO, A.A., GOMES, L.C., & LATINI, J.D. (2011). The coexistence of fish species in streams: relationships between assemblage attributes and trophic and environmental variables. Environmental Biology of Fishes, 92(1), 41–52. https://doi.org/10.1007/s10641-011-9814-2
  » https://doi.org/10.1007/s10641-011-9814-2
• BEHR, E.R., & SIGNOR, C.A. (2008). Distribuição e alimentação de duas espécies simpátricas de piranhas Serrasalmus maculatus e Pygocentrus nattereri (Characidae, Serrasalminae) do rio Ibicuí, Rio Grande do Sul, Brasil. Iheringia, Série Zoologia, 98(4): 501–507. https://doi.org/10.1590/S0073-47212008000400014
  » https://doi.org/10.1590/S0073-47212008000400014
• BRITSKI, H.A., SATO, Y., & ROSA, A.B.S. (1984). Manual de identificação de peixes da região de Três Marias: com chave de identificação para os peixes da Bacia do São Francisco. 3a ed. Brasília, Câmara dos Deputados/Codevasp, pp. 115.
• CALLISTO, M., GOULART, M., & MORETTI, M. (2001). Macroinvertebrados bentônicos como ferramenta para avaliar a saúde de riachos. Revista Brasileira de Recursos Hídricos, 6(1), 71–82. https://doi.org/10.21168/rbrh.v6n1.p71–82
  » https://doi.org/10.21168/rbrh.v6n1.p71–82
• COSTA, A.C., SALVADOR JUNIOR, L.F., DOMINGOS, F.F., & FONSECA, M.L. (2005). Alimentação da pirambeba Serrasalmus spilopleura Kner, 1858 (Characidae; Serrasalminae) em um reservatório do Sudeste brasileiro. Acta Scientiarum Biological Sciences, 27(4), 365–369. https://doi.org/10.4025/actascibiolsci.v27i4.1331
  » https://doi.org/10.4025/actascibiolsci.v27i4.1331
• COSTELLO, M.J. (1990). Predator feeding strategy and prey importance: a new graphical analysis. Journal of Fish Biology, 36, 261–263. https://doi.org/10.1111/j.1095-8649.1990.tb05601.x
  » https://doi.org/10.1111/j.1095-8649.1990.tb05601.x
• FAVARATO, R.M. (2019). Mapeamento cromossômico comparativo de serrasalmídeos (Serrasalmidae, Characiformes) por meio de sequências repetitivas de DNA. [Thesis, Instituto Nacional de Pesquisas da Amazônia].
• GÉRY, J. (1984). The fishes of Amazonia. In H Sioli (Eds.) The Amazon (pp. 353-370). Monographiae Biologicae, 56. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-6542-3_14
  » https://doi.org/10.1007/978-94-009-6542-3_14
• GOMES, J.H.C., & VERANI, J.R. (2003). Alimentação De Espécies De Peixes Do Reservatório De Três Marias. In H. P. Godinho, & A. L. Godinho (Eds.). Águas, peixes e pescadores do São Francisco de Minas Gerais (pp. 195–227). Belo Horizonte: PUC Minas, 12.
• GOULDING, M. (1980). The fishes and the forest: explorations in amazonian natural history. University of California Press.
• HAHN, N.A., AGOSTINHO, A.A., & GOITEIN, R. (1997). Feeding ecology of curvina Plagioscion squamosissimus (Hechel, 1840) (Osteichthyes, Perciformes) in the Itaipu reservoir and Porto Rico Floodplain. Acta Limnologica Brasiliensia, 9, 11–22.
• HELLAWELL, J.M., & ABEL, R.A. (1971). A rapid volumetric method for the analysis of the food of fishes. Journal of Fish Biology, 3(1), 29–37. https://doi.org/10.1111/j.1095-8649.1971.tb05903.x
  » https://doi.org/10.1111/j.1095-8649.1971.tb05903.x
• HOFFMANN, A.C., ORSI, M.L., & SHIBATTA, O.A. (2005). Diversidade de peixes do reservatório da UHE Escola Engenharia Mackenzie (Capivara), rio Paranapanema, bacia do Alto Rio Paraná, Brasil, e a importância dos grandes tributários na sua manutenção. Iheringia, Série Zoologia, 95(3), 319–325. https://doi.org/10.1590/S0073-47212005000300012
  » https://doi.org/10.1590/S0073-47212005000300012
• JÉGU, M. (2003). Subfamily Serrasalminae. In R. E. Reis, S.O. Kullander, & C. J. Ferraris Jr. (Eds.), Check List of Freshwater Fishes of South and Central America (pp. 182–196). Porto Alegre, EDIPUCRS.
• MACHADO-ALLISON, A., & GARCÍA, F. (1986). Food habits and morphological changes during the ontogeny in three serrasalmin fish species of the Venezuelan floodplains. Copeia, Lawrence, 1, 193–196.
• MASTROCHIRICO-FILHO, V.A. (2016). Análise de parentesco e variabilidade genética de pacu (Piaractus mesopotamicus) por meio de marcadores SNPs: subsídios para o melhoramento genético. [Dissertation, Universidade Estadual Paulista].
• MORAES, C.G., BRABO, L.D.M., SANTOS, A.L.S., FERREIRA, G.B., & ÂNDRADE, M. (2018). Peixe da Vez: Pygocentrus nattereri Kner, 1858. Boletim da Sociedade Brasileira de Ictiologia - SBI Nº 142 - ISSN 1808–1436.
• OLIVEIRA, L.S., CAJADO, R.A., SANTOS, L.R.B., SUZUKI, M.A.L., & ZACARDI, D.M. (2020). Bancos de macrófitas aquáticas como locais de desenvolvimento das fases iniciais de peixes em várzea do Baixo Amazonas. Oecologia Australis, 24(3), 644–660. https://doi.org/10.4257/oeco.2020.2403.09
  » https://doi.org/10.4257/oeco.2020.2403.09
• PEREIRA, C.C.G.F., SMITH, W.S., & ESPÍNDOLA, E.L.G. (2004). Hábitos Alimenticios de Nueve Especies de Peces del Embalse de Três Irmãos, São Paulo, Brasil. Universidad Y Ciencia, Número Especial I, 33–38.
• PEREIRA, L.S., AGOSTINHO, A.A., & DELARIVA, R.L. (2016). Effects of river damming in Neotropical piscivorous and omnivorous fish: feeding, body condition, and abundances. Neotropical Ichthyology, 14(1). https://doi.org/10.1590/1982-0224-20150044
  » https://doi.org/10.1590/1982-0224-20150044
• RAPOSO, R.M.G., & GURGEL, H.C.B. (2003). Variação da alimentação natural de Serrasalmus spilopleura Kner, 1860 (Pisces, Serrasalmidae) em função do ciclo lunar e das estações do ano na lagoa de Extremoz, Rio Grande do Norte, Brasil. Acta Scientiarum, 25(2), 267–272.
• RODRIGUES, D. (2013). Ecologia trófica das principais espécies de peixes do rio Paraíba do Sul na área de influência do aproveitamento hidrelétrico Simplicio durante o período pré-represamento. [Dissertation, Universidade Federal de Juiz de Fora].
• SÁNCHEZ-BOTERO, J.I., & ARAÚJO-LIMA, C.A.R.M. (2001). As macrófitas aquáticas como berçário para a ictiofauna da várzea do Rio Amazonas. Acta Amazonica, 31(3), 437–447. https://doi.org/10.1590/1809-43922001313447
  » https://doi.org/10.1590/1809-43922001313447
• SAZIMA, I., & MACHADO, F.A. (1990). Underwater observations of piranhas in western Brazil. Environmental Biology of Fishes, 28(1–4), 17–31. https://doi.org/10.1007/BF00751026
  » https://doi.org/10.1007/BF00751026
• SMITH, W.S., PETRETE JUNIOR, M., & BARRELLA, V. (2007). Fish, Sorocaba River sub-basin, state of São Paulo, Brazil. Check List, Rio Claro, 3(3), 282–286. https://doi.org/10.15560/3.3.282
  » https://doi.org/10.15560/3.3.282
• VAZ, A.A., STEFANI, M.S., & SMITH, W.S. (2018). Assembleia de peixes em um riacho tropical e os recursos alimentares explorados sob influência de mata ripária com presença de Eucalyptus grandis Acta of Fisheries and Aquatic Resources, 6(1), 61–73. https://doi.org/10.2312/Actafish.2018.6.1.61-73
  » https://doi.org/10.2312/Actafish.2018.6.1.61-73
• VILLARES JUNIOR, G.A., GOMIERO, L.M., & GOITEIN, R. (2008). Alimentação de Serrasalmus maculatus (Kner, 1858) (Characiformes; Serrasalmidae) no trecho inferior da bacia do rio Sorocaba, São Paulo, Brasil. Acta Scientiarum Biological Sciences, 30(3), 267–273. https://doi.org/10.4025/actascibiolsci.v30i3.5011
  » https://doi.org/10.4025/actascibiolsci.v30i3.5011
• WINEMILLER, K.O. (1989). Ontogenetic diet shifts and resource partitioning among piscivorous fishes in the Venezuelan llanos. Environmental Biology of Fishes 26(3), 177–199.

Edited by

• Associate Editor
  Rosana Mazzoni

Publication Dates

• Publication in this collection
  17 Aug 2026
• Date of issue
  2026

History

• Received
  28 May 2026
• Accepted
  29 July 2026