David Augusto Reynalte-Tataje1 
, Juliano Backes Scherer1, Bruna Amaral da Costa1, Rodrigo Patera Barcelos2 and Gabriela Claudia Cangahuala-Inocente1
PDF: EN XML: EN | Supplementary: S1 | Cite this article
Associate Editor: Andrea Bialetzki
Section Editor: Fernando Pelicice
Editor-in-chief: José Birindelli
Abstract
Embora os impactos das pressões antrópicas em larga escala sobre a ictiofauna sejam bem documentados, menos atenção tem sido dada à mortalidade de peixes causada pela abstração de água para irrigação. Este estudo avaliou a captura de peixes em uma lavoura de arroz no sul do Brasil, onde a água é desviada do rio Icamaquã por meio de bombas hidráulicas. Durante um período de três meses, em 2017, foram realizados 18 eventos de amostragem, tanto durante o dia quanto à noite. Os peixes capturados nos bicos de saída das bombas foram capturados com redes cônicas-cilíndricas, e amostras de ictioplâncton também foram coletadas. Após a colheita, amostragens adicionais foram realizadas no tanque de recepção, procedimento que também foi realizado em 2015. Um total de 1.082 indivíduos de 26 espécies foi registrado na saída da tubulação, com Characiformes representando mais de 98% da captura. Desses, 21,6% apresentaram lesões físicas. A amostragem de ictioplâncton resultou na captura de 132 ovos e 40 larvas. A amostragem pós-colheita revelou 3.765 indivíduos de 50 espécies, incluindo juvenis de táxons migratórios. Esses resultados destacam os riscos ecológicos da abstração de água em sistemas de irrigação de arroz, incluindo mortalidade direta, perda das fases iniciais de vida e distúrbios na estrutura da comunidade.
Palavras-chave: BBacia do Uruguai, Conservação de espécies, Gestão da irrigação, Mortalidade, Peixes migradores.
Introduction
Freshwater fish communities play a vital role in aquatic ecosystems by contributing to trophic dynamics, nutrient cycling, and overall ecological stability (Agostinho et al., 2007; Massaro et al., 2019; López-Rodriguez et al., 2019). However, these communities have been increasingly threatened by anthropogenic pressures that compromise the integrity of freshwater systems. Among the most widely recognized drivers of degradation are dams, urban and agricultural effluents, invasive species, overfishing, and climate change, factors that often interact synergistically, amplifying their ecological impacts (Agostinho et al., 2007; Pelicice et al., 2015, 2018; López-Rodriguez et al., 2024).
Within this broader context, a global threat that remains little explored for Neotropical ichthyofauna is water abstraction for agricultural purposes, particularly in flooded systems such as rice paddies (Shankar et al., 2005; Baumgartner et al., 2009). The withdrawal of large water volumes can cause substantial hydrological alterations in rivers, such as flow reduction and increased water temperature (Barletta et al., 2010). More critically, this process may lead to the unintentional entrainment of aquatic organisms, especially fish eggs, larvae, and juveniles, in artificial irrigation systems (Baumgartner et al., 2009; Pan et al., 2022). As highlighted by Wu et al. (2025), suction by motorized pumps results in severe mechanical injuries, physiological stress, and high mortality rates, particularly in systems lacking physical barriers to prevent organisms from entering the pipes. Moreover, water abstraction may facilitate the translocation of species between distinct river basins, such as translocation between the Jacuí and Uruguay basins (Barletta et al., 2010). These impacts extend to ecologically sensitive areas, including nursery and feeding grounds of migratory species (Pachla et al., 2022; Sulzbacher et al., 2023). In such habitats, larvae and juveniles may be directly entrained or indirectly affected by habitat degradation resulting from the reduction of floodplain areas that function as critical refuges and feeding sites, a direct consequence of excessive water withdrawal (Barletta et al., 2010).
The random suction of small-bodied fish and early-life stages by irrigation pumps represents a significant ecological concern since many individuals are unable to return to their natural habitats once they enter rice fields. Wu et al. (2025) emphasize that such organisms are diverted into suboptimal environments, e.g., those with low oxygen levels, agrochemical exposure, and predation risk. In Neotropical rivers, which are renowned for their high biodiversity and complex life cycles, these displacements into non-riverine environments may hinder population recruitment and disrupt ecological connectivity, particularly for migratory species that require access to multiple habitats throughout their life cycles (Agostinho et al., 2007; Pachla et al., 2022).
Brazil is the largest rice producer in South America, and the State of Rio Grande do Sul accounts for over 70% of national production of which more than eight million tons are obtained entirely under irrigation (BASF, 2025; IRGA, 2025). Cultivation with an average cycle of 100 to 120 days is concentrated between October and March, a time characterized by intensive water management, weed, pest, and disease control, and adequate fertilization. Harvesting typically occurs between February and March. Large-scale production relies predominantly on continuous flood irrigation which demands substantial water volumes that average 6,000 to 12,000 m³/ha (0.70–1.75 L/s ha) over 80 to 100 days, depending on soil type, slope, and climatic regime (ANA, 2009; FEPAM, 2018; SOSBAI, 2022). In Rio Grande do Sul, approximately 80% of cultivated areas depend on high-capacity pumping stations to abstract water from rivers, canals, or reservoirs (Köpp et al., 2016). In this context, the Icamaquã River, an important tributary of the middle Uruguay River, supports floodplain habitats, high fish diversity, and migratory species at different developmental stages (Massaro et al., 2019; Pachla et al., 2022). Its margins, like those of other rivers in the region, are bordered by extensive rice fields whose water demand intensifies during summer and in La Niña years when rainfall is naturally reduced (Pandolfo et al., 2002).
Despite potential ecological consequences, the impacts of agricultural water abstraction on freshwater fish communities remain poorly studied in Brazil. To address this knowledge gap, the present study evaluated the effects of water abstraction associated with rice cultivation on the ichthyofauna of the Icamaquã River. During fieldwork, we aimed to (i) verify and quantify fish entrained by suction pumps, (ii) characterize the taxonomic composition of captured aquatic organisms with emphasis on large-bodied and migratory species, (iii) assess whether fish entrainment differs between daytime and nighttime, (iv) examine the occurrence of injuries in entrained fish, and (v) discuss the ecological risks associated with current irrigation practices with the overall goal of informing public policy and environmental management strategies. The tested hypotheses hold that (i) fish at different life stages are entrained by suction pumps, including large-bodied and migratory species, (ii) both the composition and abundance of entrained ichthyofauna differ between daytime and nighttime, and (iii) fish entering through suction may present with physical injuries.
Material and methods
Study area. The study was conducted at Fazenda Figueira, which is located in the municipality of São Borja in the southern region of Rio Grande do Sul, Brazil (Fig. 1). The farm, which spans 336.84 ha dedicated to irrigated rice cultivation, is situated adjacent to the lower stretch of the Icamaquã River, only a few hundred meters from its confluence with the Uruguay River. Irrigation is carried out through a direct pumping system from the Icamaquã. This river extends for 250 km, originating in the municipality of Santiago and flowing through extensive agricultural areas primarily used for rice cultivation before reaching the Uruguay River. Near its mouth, the Icamaquã is approximately 80 m wide and 5.5 m deep on average. The pumping station at Fazenda Figueira is located on the river’s left bank (28º38’22”S 56º03’59”W) and is equipped with three 40-HP hydraulic pumps which, together, withdraw between 300 and 400 m³/h of water to supply the rice fields (Fig. 2).
FIGURE 1| Location of the studied rice field on the Icamaquã River, Rio Grande do Sul, Brazil.
FIGURE 2| Schematic of the pumping station at Figueira Farm.
The water intake system consists of three pump outlets responsible for channeling water from the river to the cultivated areas. Each pipe has a diameter of 55 cm and features a protective grille at the inlet with an opening of 4 cm². The water drawn from the river travels for approximately 40 m before reaching an earthen tank measuring 288 m² with a depth of 3 m. This excavated tank, positioned at ground level and aligned with the rice channels, serves to receive the large volume of water; otherwise, water directly released into rice channels would end up eroding them. The water immediately overflows from the surface of the tank into the rice cultivation channels where the level varies, but does not exceed 50 cm in depth. Owing to the high-water turnover in the intake tank, water quality parameters in this environment, while the pumps are operating, are very similar to those recorded in the river. However, water quality deteriorates drastically throughout the system when pumping is interrupted.
Sampling. Between January and March of 2017, fish entrainment by irrigation pumps was assessed. To sample fish drawn into the system, conical-cylindrical nets were installed at the outlet of the pipes discharging into the receiving tank. These nets were securely fastened with bolts to ensure stable placement. Each net measured 200 cm in length with a 60 cm mouth diameter and 5 mm mesh size (Figs. 3A–B).
FIGURE 3| Sampling net used to capture juveniles and adults entrained by the pumps (A); installation of the net at the pipe outlet for fish capture (B).
Sampling was conducted twice a day, once during daylight hours (08:00–12:00) and once at night (18:00–22:00), to assess diel variation in fish entrainment. Each session lasted four hours and was repeated three times per month during the summer, totaling 18 samples (9 daytime and 9 nighttime). The fish captured at the pipe outlet were identified and measured for weight (g) and total length (mm). Based on a physical examination, individuals were further classified into three categories: (1) uninjured, (2) minor injuries, and (3) severe injuries with a high probability of mortality or already dead. Additionally, fish were categorized by taxon as migratory or non-migratory species, following Massaro et al. (2019), and by adult size: small (< 150 mm), medium (150–300 mm), and large (> 300 mm). In addition to fish captures, an ichthyoplankton survey was carried out at night. A 2-m fine-mesh (0.5 mm) conical-cylindrical plankton net with a 38 cm mouth diameter was deployed for 10 minutes at the outlet of one of the discharge pipes to detect the presence of fish eggs and larvae. This procedure was conducted once per sampling day across the three days of each month. Nighttime sampling was prioritized based on evidence from previous ichthyoplankton studies indicating higher concentrations of early-life stages in the water column during nocturnal hours (Hermes-Silva et al., 2009; Sulzbacher et al., 2023).
As a complement to assessment of the potential impact of rice fields on fish assemblages, an additional sampling campaign was conducted in the receiving tank following the cessation of pumping activities and the subsequent decline in water level. This took place in early April 2017 when the water level in the tank dropped below 80 cm. A 5 m seine net was used to capture all remaining fish in the tank. At the end of the 2014/2015 rice growing season, a similar procedure was performed in March of 2015 to serve as a comparative dataset.
Fish eggs and larvae were euthanized using eugenol and subsequently fixed in 4% buffered formalin before being stored in 500 mL containers. Juvenile and adult fish were also euthanized with eugenol, fixed in 10% formalin and stored in 30 L plastic drums. All samples were then transported to the laboratory of the Universidade Federal da Fronteira Sul (UFFS), Cerro Largo campus, where ichthyoplanktons were sorted and identified, and juvenile and adult specimens were identified and measured. Taxonomic identification was based on established reference literature (Nakatani et al., 2001; Zaniboni-Filho et al., 2004; Ota et al., 2018; Fricke et al., 2025). Voucher specimens were deposited in the Fish Collection of the Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupélia), at the Universidade Estadual de Maringá, Maringá, Paraná, Brazil (Tab. 1; Tab. S1).
TABLE 1 | List of taxa, vouchers, and larval stages of fish captured with an ichthyoplankton net at the suction pipe outlet in the rice field in São Borja, Rio Grande do Sul, from January to March 2017.
Taxa | Month |
|
| ||
January | February | March | Total | Vouchers | |
Characiformes | |||||
Anostomidae | 4 |
|
| 4 |
|
Astyanax lacustris | 1 | 1 |
| 2 | NUP 23391 |
Characidae | 5 | 4 | 4 | 13 |
|
Holoshestes pequira | 4 | 2 |
| 6 |
|
Oligosarcus sp. | 1 |
|
| 1 | NUP 23393 |
Piabarchus stramineus | 2 | 1 | 1 | 4 | NUP 23408 |
Steindachnerina sp. | 1 |
|
| 1 |
|
Siluriformes | |||||
Hoplosternum littorale | 1 |
|
| 1 |
|
Hypostomus sp. | 1 |
|
| 1 |
|
Loricariichthys sp. | 3 | 1 |
| 4 | NUP 90922 |
Microglanis sp. |
| 1 |
| 1 |
|
Pimelodella gracilis |
| 1 |
| 1 | NUP 20907 |
Unidentified |
|
| 1 | 1 |
|
DEVELOPMENTAL STAGES | |||||
Yolk-sac |
|
|
| 11 |
|
Preflexion |
|
|
| 28 |
|
Flexion |
|
|
| 1 |
|
Postflexion |
|
|
| 0 |
|
Data analysis. To evaluate any significant differences in total number of species and total number of individuals between diel periods (daytime and nighttime), a One-way Analysis of Variance (ANOVA) was applied since the data satisfied the assumptions. Group homoscedasticity and residual normality were evaluated using Levene’s test and the Kolmogorov-Smirnov Test, respectively.
To summarize the structure of fish assemblages sampled during different periods of the day, a Detrended Correspondence Analysis (DCA) was performed based on abundance data. Only species recorded in more than two samples were included in the analysis to minimize the influence of rare or isolated occurrences. Detrended Correspondence Analysis axes that showed eigenvalues higher than expected by chance were retained for interpretation (Legendre, Legendre, 2012). Differences between groups identified by ordination were tested using the Multi-Response Permutation Procedure (MRPP). To assess potential differences between total lengths of fish captured during day and night, a t-test was applied.
All statistical analyses were conducted using PcOrd v. 5.0 and RStudio v. 3.4.0. A significance level of α = 0.05 was adopted for all tests.
Results
Eggs and larvae. A total of 132 eggs and 40 larvae were collected from the water entering the reception tank of the rice field. Most larvae were at the yolk-sac (YS; 27.5%) and preflexion (PF; 70.0%) developmental stages. No postflexion larvae were observed, and only a single individual was identified at the flexion stage. The recorded taxa were predominantly composed of small- and medium-sized species, and none of the captured larvae belonged to migratory or endangered species (Tab. 1).
Juveniles and adults. Comparative assessment of diurnal and nocturnal entry of fish into the field. Over the three-month study period, a total of 1,082 fish were captured upon entering the reception tank. These individuals belonged to 26 species distributed across three taxonomic orders. Among them, Characiformes accounted for 98.4% of the total catch, followed by Siluriformes (1.3%) and Cichliformes (0.3%). The assemblage was dominated by small-sized Characiformes, particularly Astyanax lacustris, Holoshestes pequira, and Serrapinnus calliurus, which, together, accounted for over 85% of all individuals. Most captured specimens were adults of small-sized species with comparatively fewer juveniles of medium- and large-sized fishes presenting 17% and 2%, respectively. Among the larger species, two migratory taxa, Megaleporinus obtusidens and Prochilodus lineatus, were also recorded (Fig. 4).
FIGURE 4| Taxonomic composition of fish captured during diurnal and nocturnal periods between January and March 2017 in the rice fields of São Borja, Rio Grande do Sul.
Additionally, a total of 234 entrained fish (21.6%) showed some type of injury. Most fish showed only minor marks, but about 1 (about 20% of the total) in every 5 individuals with injuries exhibited deep cuts in various parts of the body.
During the four-hour intervals when the net was deployed at the pump outlet, the mean number of species captured during the day was twice that recorded at night (12 vs. 6 species, respectively; Fig. 5A). Conversely, the mean number of individuals captured at night (82.6 individuals) was significantly higher than that during the day (37.7 individuals; Fig. 5B). The estimated capture rates were 20.6 fish per hour at night and 9.4 fish per hour during the day.
FIGURE 5| Analysis of Variance (ANOVA) applied to (A) the number of species captured and (B) the number of individuals captured during daytime and nighttime periods in a rice field in São Borja, Rio Grande do Sul, from January to March 2017.
Axes 1 and 2 of the DCA presented eigenvalues greater than those generated by chance and were therefore retained for interpretation. In the DCA plot, daytime and nighttime sampling points showed a slight segregation which was statistically confirmed by the MRPP test (T= -3.39, A= 0.13; P < 0.05).
Among the species predominantly associated with the daytime period were Aphyocharax anisitsi and Psalidodon rutilus, the anostomids Leporinus amae, Brevidens striatus, and M. obtusidens, as well as the cichlid Cichlasoma dimerus. In contrast, the species most associated with the nighttime period included the small Characiformes A. lacustris and H. pequira, which were abundantly captured during this time. (Figs. 6A–B).
FIGURE 6| Detrended Correspondence Analysis (DCA) based on the first two axes, using the fish capture data matrix from rice fields in São Borja, Rio Grande do Sul, from January to March 2017, comparing daytime and nighttime periods. A. Ordination of sampling periods; B. Ordination of recorded taxa.
The Fig. 7 shows the histogram of fish distribution by size classes and the proportion of individuals belonging to small-, medium-, and large-sized species. The highest number of fish captured fell within the 71–90 mm range with the overall size of captured fish ranging from 16 to 152 mm. No statistically significant difference in fish size was observed between day and night (T = -0.27; P > 0.05).
FIGURE 7| Total length distribution of fish by size class captured at the rice field inlet, São Borja, Rio Grande do Sul, Brazil. Size categories: S = Small; M = Medium; L = Large.
Final fish harvest from the reception tank at the end of the cultivation period. Over the two years (March 2015 to April 2017) during which the harvest from the inlet tank to the rice field was conducted, a total of 50 fish species were recorded, comprising 3,765 individuals from 20 families across four different taxonomic orders. In 2017, when variation in capture rates during both daytime and nighttime periods was also assessed, both the number of species and the number of individuals were nearly twofold those recorded in 2015. However, the highest richness and abundance of migratory taxa occurred in 2015, driven primarily by the capture of 144 P. lineatus, 31 Salminus brasiliensis, and 12 Brycon orbignyanus individuals (Tab. 2).
TABLE 2 | Taxonomic composition of fish captured in the water reception tank at the end of the cultivation period on a rice farm in São Borja, Rio Grande do Sul (March 2015 and April 2017). *Threatened species in the Uruguay River basin.
Taxa | Year | |
2015 | 2017 | |
CHARACIFORMES | ||
Acestrorhamphidae | ||
Astyanax lacustris | 637 | 776 |
Megalamphodus eques |
| 1 |
Moenkhausia bonita |
| 2 |
Oligosarcus jenynsii |
| 1 |
Psalidodon henseli | 9 | 2 |
Psalidodon rutilus | 3 | 54 |
Psalidodon xiru | 7 | 4 |
Anostomidae | ||
Leporinus amae |
| 3 |
Brevidens striatus |
| 3 |
Megaleporinus obtusidens | 2 | 14 |
Schizodon nasutus |
| 3 |
Bryconidae | ||
Brycon orbignyanus* | 12 |
|
Salminus brasiliensis* | 31 |
|
Characidae | ||
Aphyocharax anisitsi |
| 66 |
Charax leticiae | 6 | 15 |
Holoshesthes pequira |
| 938 |
Roeboides microlepis |
| 23 |
Roeboides paranensis |
|
|
Serrapinnus calliurus | 101 | 170 |
Crenuchidae | ||
Characidium serrano |
| 2 |
Curimatidae | ||
Cyphocharax saladensis |
| 1 |
Cyphocharax voga |
|
|
Steindachnerina brevipinna | 218 | 122 |
Erythrinidae | ||
Hoplias australis |
| 1 |
Hoplias missioneira | 4 | 8 |
Parodontidae | ||
Apareiodon affinis | 31 | 64 |
Prochilodontidae | ||
Prochilodus lineatus | 144 | 13 |
Serrasalmidae | ||
Serrasalmus maculatus | 1 |
|
Stevardiidae | ||
Bryconamericus iheringii | 3 | 4 |
Cyanocharax alburnus |
| 120 |
Piabarchus stramineus | 58 | 18 |
CICHLIFORMES | ||
Cichlidae | ||
Cichlasoma dimerus | 1 | 21 |
Crenicichla missioneira |
| 1 |
Crenicichla vittata |
| 1 |
Geophagus iporangensis |
| 2 |
Gymnogeophagus sp. | 5 |
|
Saxatilia lepidota |
| 1 |
ACANTHURIFORMES | ||
Sciaenidae | ||
Pachyurus bonariensis | 2 |
|
SILURIFORMES | ||
Aspredinidae | ||
Bunocephalus doriae |
| 2 |
Auchenipteridae | ||
Auchenipterus osteomystax | 1 |
|
Trachelyopterus galeatus |
| 2 |
Trachelyopterus lucenai |
| 1 |
Callichthyidae | ||
Hoplosternum littorale |
| 5 |
Doradidae | ||
Rhinodoras dorbignyi | 1 |
|
Heptapteridae | ||
Pimelodella gracilis |
| 4 |
Rhamdella longiuscula | 2 |
|
Rhamdia quelen | 8 | 5 |
Loricariidae | ||
Hypostomus roseopunctatus |
| 1 |
Loricariichthys platymetopon |
| 1 |
Rineloricaria sp. |
| 1 |
Pimelodidae | ||
Iheringiichthys labrosus | 1 |
|
Trichomycteridae | ||
Paravandellia oxyptera |
| 1 |
TOTAL | 1288 | 2477 |
Fish captured in the reception tank were predominantly from small-bodied species or juveniles of medium- and large-bodied species. Furthermore, more than 98% of all individuals belonged to the order Characiformes, and within this group, the Acestrorhamphidae and Characidae families were the most representative.
Discussion
The use of suction pumps in irrigated rice farming has become increasingly widespread (Carney, 1998; Barletta et al., 2010; Baird et al., 2015; Nguyen et al., 2019). These systems are essential for sustaining water supply throughout the cultivation cycle, particularly in areas with limited natural resources or during droughts. Yet, our findings demonstrate that this irrigation method can exert ecological pressures on local fish assemblages. Suction pumps indiscriminately entrain organisms across multiple life stages, from ichthyoplankton (eggs and larvae) to juveniles and small-bodied adults, none of which are able to withstand the hydraulic forces at the pump intake.
In southern Brazil, water abstraction for rice cultivation occurs mainly from October to March, coinciding with the crop cycle (Steinmetz, Braga, 2001). Pumping activity intensifies during summer droughts and La Niña events when low rainfall leads to nearly continuous operation (Britto et al., 2008; Soares et al., 2022). Critically, this period overlaps with the reproductive and recruitment seasons of many fish species (Massaro et al., 2019; Soares et al., 2022; Sulzbacher et al., 2023), magnifying the potential for population-level effects.
Fish entrainment in rice fields. During our 72 h sampling, 1,082 individuals representing 26 species were entrained at the pump outlets, including juveniles of medium- and large-bodied species and adults of small-bodied taxa, all under 160 mm in length. This short sampling window captured nearly one-quarter of the total fish diversity reported for the middle Uruguay River in a year-long survey (Massaro et al., 2019), underscoring the intensity of organism removal. By comparison, Baumgartner et al. (2009) documented only 11 species entrained over ten weeks of monitoring in the Namoi River, Australia, with up to 232 individuals per day. The scale of impact in Rio Grande do Sul is further amplified by the extent of rice cultivation. Indeed, nearly one million hectares were planted in 2024/2025 (IRGA, 2025), largely irrigated with water diverted from the Uruguay River basin. The absence of return pathways in most pumping systems prevents entrained fish from escaping or recolonizing natural habitats.
Although Characiformes and Siluriformes dominate the basin’s ichthyofauna (Reynalte-Tataje et al., 2012; Massaro et al., 2019; Pachla et al., 2022), susceptibility to entrainment was highly uneven. For every 50 Characiformes recorded, only one Siluriform was captured. This discrepancy likely reflects their contrasting ecological niches wherein Characiformes occupy the water column, while Siluriformes are benthic (Reynalte-Tataje et al., 2012), as well as differences in sensitivity to hydraulic stress. At the end of the cultivation cycle, more than 3,000 individuals from 50 taxa were trapped in intake tanks (2015 and 2017 seasons), including juveniles of critically endangered migratory species, such as Brycon orbignyanus and Salminus brasiliensis (Rio Grande do Sul, 2014), along with M. obtusidens and P. lineatus, both subject to severe regional declines (Agostinho et al., 2007; Massaro et al., 2019; Reynalte-Tataje et al., 2020). These captures likely underestimate total impacts since irrigation channels were not sampled, even though fish schools were frequently observed within rice paddies.
Injury and mortality. Although many individuals survived passage through the pumps without visible damage, 21.6% exhibited injuries, a value far exceeding the 7.5% reported in a comparable Australian study (Baumgartner et al., 2009). In Rio Grande do Sul, centrifugal and axial-flow pumps are most common (Köpp, 2015; Köpp et al., 2016). Unlike “fish-friendly” technologies implemented elsewhere (Amaral et al., 2011; Jacobson, 2011; Pan et al., 2022), these systems lack design features to minimize injury or mortality. Furthermore, while Brazilian regulations stipulate protective screens with mesh sizes ≤1 cm² (SUDEPE, 1982), the study site employed screens with 4 cm² openings, contributing to both high entrainment and injury rates. Weak enforcement and frequent clogging of screens, which threatens pump function, further undermine compliance.
Temporal patterns of capture. Behavioral patterns have been considered in managing water abstraction with some studies reporting diel variation in entrainment rates (Carter, Reader, 2000; Baumgartner et al., 2009). Our results, however, showed an inconclusive pattern in that more species were captured during the day, whereas the number of individuals was greater at night. These findings suggest that timing withdrawal to minimize fish losses may not be straightforward and that further studies with longer temporal coverage are needed to assess its feasibility.
Global context and ecological implications. Globally, the ecological consequences of irrigation-driven water withdrawal are well established. In Bangladesh, models predict fishery collapse under continued abstraction (Shankar et al., 2005), while in Australia’s Murray-Darling basin, ~80% of river flow is diverted without measures to prevent fish entry (King, O’Connor, 2007). In Brazil, where centrifugal pumps predominate, large water volumes, intensive schedules, and the lack of return routes trap fish in suboptimal habitats where they face predation, pesticide exposure, and eventual desiccation.
Impact assessment, management, and mitigation. Addressing these impacts requires integrated mitigation strategies, including fish-friendly pumps, finer filtration systems, behavioral deterrents, and operational guidelines, approaches already tested in hydroelectric and agricultural systems elsewhere (Hecker et al., 2005; Agostinho et al., 2007; Algera et al., 2020; Radinger et al., 2021; Pan et al., 2022). Despite growing recognition of the ecological effects of dams and hydropower in Brazil (Agostinho et al., 2007; Pelicice et al., 2015; Azevedo-Santos et al., 2024), agricultural drivers, such as irrigation, remain understudied. Our results show that water abstraction during peak reproductive and larval development periods can severely compromise migratory fish recruitment, along with cascading effects on community structure and ecosystem functioning across the basin.
The results of this study show that rice fields have impacts on fish communities. The unintentional capture and subsequent mortality of fish indicate that the observed diversity and abundance likely represent only a fraction of the negative effects of rice irrigation. These cumulative impacts highlight the need for policies that promote mitigation technologies, supported by long-term monitoring and adaptive management. The conservation of aquatic biodiversity in agricultural landscapes will depend on the integration of scientific evidence, technological innovation, and effective governance.
Acknowledgments
The authors thank the fishermen who assisted with samplings.
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Authors
David Augusto Reynalte-Tataje1 , Juliano Backes Scherer1, Bruna Amaral da Costa1, Rodrigo Patera Barcelos2 and Gabriela Claudia Cangahuala-Inocente1
[1] Programa de Pós-Graduação em Ambiente e Tecnologias Sustentáveis (PPGATS), Universidade Federal da Fronteira Sul (UFFS), Campus Cerro Largo, Av. Jacob Reinaldo Haupenthal, 1580, Bairro São Pedro, 97900-000, Cerro Largo, RS, Brazil. (DART) david.tataje@uffs.edu.br (corresponding author), (JBS) juliano_scherer1992@hotmail.com, (BAC) bru.bio@hotmail.com, (GCCI) gcangahu@hotmail.com.
[2] Universidade Federal da Fronteira Sul (UFFS), Campus Cerro Largo, Av. Jacob Reinaldo Haupenthal, 1580, Bairro São Pedro, 97900-000, Cerro Largo, RS, Brazil. (RPB) rodrigo.barcelos@uffs.edu.br.
Authors’ Contribution 
David Augusto Reynalte-Tataje: Conceptualization, Resources, Data curation, Investigation, Formal analysis, Methodology, Software, Writing-original draft, Writing-review and editing.
Juliano Backes Scherer: Conceptualization, Data curation, Investigation, Methodology, Writing-review and editing, Software.
Bruna Amaral da Costa: Investigation, Writing-review and editing.
Rodrigo Patera Barcelos: Methodology,Resources, Investigation.
Gabriela Claudia Cangahuala-Inocente: Investigation, Writing-original draft, Writing-review and editing.
Ethical Statement
We declare that during the field activities, individuals obtained were euthanized following the guidelines established by the Conselho Nacional de Controle e Experimentação Animal (CONCEA, 2013) and approved by the ethics committee of the Universidade Federal da Fronteira Sul with the registered protocol number 23205.004977/2015–90. This study is part of Project 534 entitled ‘Fish Ecology of the Middle Uruguay’ carried out under licenses 55011–2 (ICMBio).
Competing Interests
The author declares no competing interests.
Data availability statement
The data supporting the findings of this study are available from the corresponding author upon reasonable request.
AI statement
Artificial intelligence (ChatGPT) was used exclusively for the final text revision, with the aim of improving textual cohesion, and for the translation of the manuscript.
Funding
This study received funding from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the scholarship granted to JBS and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) via scholarship granted to BCA.
Supplementary Material
Supplementary material S1
How to cite this article
Reynalte-Tataje DA, Scherer JB, Costa BA, Barcelos RP, Cangahuala-Inocente GC. Vulnerability of rheophilic fishes to water abstraction in pump-irrigated rice fields in southern Brazil. Neotrop Ichthyol. 2025; 23(4):e250080. https://doi.org/10.1590/1982-0224-2025-0080
Copyright
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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© 2025 The Authors.
Diversity and Distributions Published by SBI
Accepted October 30, 2025
Submitted May 6, 2025
Epub February 2, 2026