Fish diversity in artificial and natural wetlands in the Sinos River floodplain, Southern Brazil

Kelly Correia de Lima¹, Caroline dos Santos Brückmann², Ana Caroline Ruppenthal³, Amanda Bauer³, Marlon Ferraz³ and Uwe Horst Schulz³

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Associate Editor: Ana Cristina Petry

Section Editor: Fernando Pelicice

Editor-in-chief: José Birindelli

Abstract​

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Introduction​

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With their high biological diversity and numerous ecosystem services, wetlands are strategic conservation sites since they are among the richest and most productive aquatic ecosystems in the world (Mitsch, Gosselink, 2000; Kingsford et al., 2021). At the same time, they are one of the most vulnerable and threatened ecosystems, mainly due to the high anthropic pressure, caused by the expansion of agriculture, urban areas, silting, drainage and pollution (Bunster et al., 2021). The conversion of wetlands into artificial ecosystems such as agricultural (rice paddies, aquaculture) and urban areas is one of the principal impacts caused by human activities (Vitousek, 1994). To alleviate this trend several management strategies for the conservation of these threatened ecosystems have been developed (Mitsch, 2005). One of these strategies is the construction of artificial wetlands (Vymazal, 2011). Artificial wetlands are intentionally built for sewage treatment (Levy, 2015), for compensation of a natural land loss due to land use changes (Campbell et al., 2002) and for biodiversity conservation (De Martis et al., 2016). But they are also formed unintentionally, as by-products of soil moving activities such as clay extraction to produce bricks and roof tiles. Artificial wetlands resemble and can function like natural areas (Galatowitsch, Van der Valk, 1994). However, physical similarity may not lead to functional substitution of its faunal or vegetational elements (Campbell et al., 2002). In many regions of the world, the construction of artificial wetlands is an attempt to compensate for the loss of natural wetlands and their impacts (Ma et al., 2004). The construction of artificial wetlands has been a strategy widely used to provide habitat for birds, and these studies have shown that, on average, natural wetlands harbour higher species richness and support greater abundances (Wang et al., 2016). However, other studies show that artificial wetlands have the potential to support communities similar to natural wetlands in terms of biodiversity and composition (Bellio et al., 2009; Giosa et al., 2018; Ma et al., 2004).

The Sinos River, located in the state of Rio Grande do Sul, in the extreme south of Brazil, is a heavily polluted river that receives the sewage of approximately 1.8 million people (Steffens et al., 2015). Until 1800, the basin was occupied only by indigenous peoples. The first European immigrants arrived in 1820 and massive and coordinated colonization began in 1824, when the first German immigrants arrived and were distributed by the Brazilian authorities in the basin (Hunsche, 1975). Early colonization activities included the extraction of clay in the river floodplain, to produce construction material, principally bricks and roof tiles. These extraction sites of clay in the floodplain were rapidly filled with water, or by the high ground water level or by the annual floods of the Sinos River. During these cyclically occurring floods propagules of aquatic vegetation, macroinvertebrates, fish, and other elements of the aquatic ecosystem are dispersed in the inundated floodplain.

Nowadays, the Sinos River basin stands out as one of the most populous and industrialized river basins in Brazil. It occupies 1.3% of the area of the State of Rio Grande do Sul but generates almost 20% of the state’s Gross Domestic Product (Figueiredo et al., 2010).

The high population density generates large quantities of organic sewage. Approximately 90% of the sewage is not adequately treated, causing a decrease in water quality, particularly close to the urban centers in the lower part of the river basin (Blume et al. 2010; Pedde et al., 2015). The riparian vegetation is almost completely removed or exists in buffer strips generally less than five meters wide in large parts of the stream network of the basin (Viegas et al., 2014). A recent study of Brückmann (2021) showed a decrease of the wetland area in the Sinos River floodplain by 22.5% between 1985 and 2020. Considering the most recent catastrophic floods in the Rio Grande do Sul State, wetland conservation for maintaining the floodplain function of absorbing the excess flood water is crucial for the river basin management (Schulz et al., 2021). Artificial wetlands could at least compensate a part of the loss of natural wetlands (Brückmann, 2021; Vymazal, 2011; Kadlec et al., 2012).

The present study focusses on the ecological functionality of artificial wetlands created by clay extraction, by comparing the fish diversity metrics of species richness, abundance, Shannon diversity, equitability and fish community composition with neighbouring natural wetlands. Since all wetlands are subjected to annual flooding which favours species dispersal, we tested the null hypotheses that these parameters do not differ between the two wetland types.

Material and methods

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Study area.The study area comprises the floodplain of Sinos River basin, in Brazil´s southernmost State Rio Grande do Sul (Fig. 1). The Sinos River main stem has an approximate length of 190 km. Its source is located in the municipality of Caraá and its mouth is located in the Delta do Jacuí, in the municipality of Canoas, flowing into the Guaíba Lake near the state’s capital Porto Alegre (Anschau, 2016).

FIGURE 1| A. South America and Brazil (black polygon). B. State of Rio Grande do Sul (black polygon) in Brazil. C. Sinos River basin (black polygon). D. Sample sites in the Sinos River floodplain. Blue lines are the stream network of the basin. The sample sites in natural wetlands are green dots, artificial wetlands are red dots. Two sample sites are overlaid. Flow direction in the river main stem is from east to west.

The basin covers 32 municipalities. The highest population density and industrial activity is located in its lower portion (Bieger et al., 2010). Economical activities in the middle and upper section include rice plantations and livestock, converting natural vegetation cover into agricultural land use (Bieger et al., 2010; Figueiredo et al., 2010). The regional climate is subtropical, with annual precipitation between 1,200 and 2,000 mm, well distributed throughout the year. The Sinos River basin is inserted in the phytophysiognomy of the Semideciduous Seasonal Forest, within the Atlantic Forest Biome (Bieger et al., 2010).

Sampling proceedings. Fish were sampled between November 2014 and June 2015 at twelve sites, of which six were of artificial origin and six were natural wetlands (Fig. 2). All collection sites were located in the river floodplain within a distance of 100 m and 600 m from the main river channel. Artificial wetlands originated from the extraction of clay for brick and roof tile production. At each site, fish were collected by electric fishing (750V unpulsed direct current; EFKO FEG 800 7.5KW, Germany) with a standard fishing effort of 20 min. The water parameters dissolved oxygen, conductivity, turbidity and oxygen reduction potential were measured at each sampling site by a Horiba U-50 multi parameter probe.

FIGURE 2| A. Artificial wetland, created by clay extraction; B. Natural wetland. Photos by Uwe H. Schulz.

Data analysis. Sampling efficiency was analysed by individual based rarefaction (Heck et al., 1975). We generated interpolation and extrapolation curves with 95% confidence intervals, allowing assessment of the sampling effort sufficiency and the comparability of species richness between wetland types. Data were organized into an abundance matrix, grouped by wetland type (natural or artificial), and subjected to analysis for q = 0, corresponding to species richness.

The means offish species richness and abundance per sample site were compared by the Student-T test after analysing normality by Shapiro-Wilk. The mean Shannon diversity indices were compared by the T-test modification of Hutcheson (1970) and mean equitability by the non-parametric Mann-Whitney test. Linear regression between relative species abundances in the artificial and natural wetlands was applied to analyse the similarity of fish communities in both classes. A significant relationship indicates a high similarity between both communities.

Additionally, the mean environmental parameters of dissolved oxygen (mg/L), conductivity (mS/cm), turbidity (NTU) and oxidation-reduction potential (mV) of both wetland types were compared as well by the Student T-test, since data were normally distributed as indicated by the Shapiro-Wilk-test. All tests were performed using IBM SPSS Statistics 26 package (IBM Corp., 2019). Significance level was 0.05 for all tests.

Results​

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A total of 2,726 individuals distributed in 38 species of 14 different families was captured in both wetland types (Tab. 1). All captured species but one (Acestrorhynchus pantaneiro) belonged to native fish of the Sinos River basin.

TABLE 1 | List of species with orders, families, absolute and relative abundances in artificial and natural wetlands in the Sinos River floodplain (MZU, Coleção de Zoologia Unisinos; MCP, Museu de Ciências e Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul).

Taxa	Artificial		Natural		Voucher species
	n	%	n	%
CHARACIFORMES
Acestrorhynchidae
Acestrorhynchus pantaneiro Menezes, 1992	4	0.23	0	0	MZU_PEIXES 811
Acestrorhamphidae
Astyanax lacustris (Lütken, 1875)	113	6.51	4	0.4	MCP 52598
Deuterodon luetkenii (Boulenger, 1887)	350	20.16	187	18.89	MZU_PEIXES 111
Hyphessobrycon bifasciatus Ellis, 1911	10	0.58	0	0	MZU_PEIXES 1589
Hyphessobrycon boulengeri (Eigenmann, 1907)	76	4.38	75	7.58	MZU_PEIXES 1285
Hyphessobrycon meridionalis Ringuelet, Miquelarena & Menni, 1978	0	0	18	1.85	MZU_PEIXES 1291
Oligosarcus robustus Menezes, 1969	19	1.09	18	1.82	MZU_PEIXES 841
Psalidodon eigenmanniorum (Cope, 1894)	2	0.12	25	2.53	MZU_PEIXES 1588
Psalidodon fasciatus (Cuvier, 1819)	129	7.43	84	8.48	MZU_PEIXES 1415
Psalidodon henseli (de Melo & Buckup, 2006)	8	0.46	0	0	MZU_PEIXES 110
Characidae
Aphyocharax anisitsi Eigenmann & Kennedy, 1903	20	1.15	1	0.1	MZU_PEIXES 1502
Charax stenopterus (Cope, 1894)	3	0.17	0	0	MZU_PEIXES 131
Cheirodon ibicuhiensis Eigenmann, 1915	117	6.4	96	9.7	MZU_PEIXES 157
Macropsobrycon uruguayanae Eigenmann, 1915	0	0	8	0.82	MCP 11930
Stevardiidae
Diapoma alburnus (Hensel, 1870)	16	0.92	0	0	MZU_PEIXES 1601
Pseudocorynopoma stanleyi Malabarba, Chuctaya, Hirschmann, Oliveira & Thomaz, 2020	79	4.55	39	3.94	MZU_PEIXES 1417
Crenuchidae
Characidium orientale Buckup & Reis, 1997	13	0.75	0	0	MZU_PEIXES 156
Characidium pterostictum Gomes, 1947	0	0	1	0.1	MZU_PEIXES 34
Characidium tenue (Cope, 1894)	3	0.17	1	0.1	MZU_PEIXES 681
Characidium zebra Eigenmann, 1909	4	0.23	30	3.03	MZU_PEIXES 885
Curimatidae
Cyphocharax saladensis (Meinken, 1933)	34	1.96	8	1.54	MCP 18587
Cyphocharax spilotus (Vari, 1987)	0	0	24	2.42	MCP 26008
Cyphocharax voga (Hensel, 1870)	211	12.15	112	11.31	MZU_PEIXES 810
Steindachnerina biornata (Braga & Azpelicueta, 1987)	116	6.68	53	5.35	MZU_PEIXES 161
Erythrinidae
Hoplias malabaricus (Bloch, 1794)	8	0.46	12	7.42	MZU_PEIXES 174
CICHLIFORMES
Cichlidae
Australoheros acaroides (Hensel, 1870)	1	0.06	0	0	MZU_PEIXES 184
Cichlasoma portalegrense (Hensel, 1870)	13	0.75	35	3.54	MZU_PEIXES 272
Geophagus iporangensis Haseman, 1911	15	0.86	20	2.02	MZU_PEIXES 1462
Gymnogeophagus gymnogenys (Hensel, 1870)	165	9.5	43	4.34	MZU_PEIXES 307
Gymnogeophagus rhabdotus (Hensel, 1870)	144	8.29	74	7.47	MZU_PEIXES 1666
Saxatilia lepidota Heckel, 1840)	25	1.44	15	1.52	MZU_PEIXES 648
CLUPEIFORMES
Engraulidae
Platanichthys platana (Regan, 1917)	26	1.5	0	0	MZU_PEIXES 155
CYPRINODONTIFORMES
Poeciliidae
Phalloceros caudimaculatus (Hensel, 1868)	0	0	3	0.3	MZU_PEIXES 102
GYMNOTIFORMES
Sternopygidae
Eigenmannia trilineata López & Castello, 1966	1	0.06	0	0	MZU_PEIXES 1542
SILURIFORMES
Callichytidae
Hoplisoma paleatum (Jenyns, 1842)	8	0.46	3	1.21	MZU_PEIXES 103
Loricariidae
Rineloricaria cadeae (Hensel, 1868)	2	0.12	0	0	MZU_PEIXES 248
Rineloricaria microlepidogaster (Regan, 1904)	0	0	1	0.1	MZU_PEIXES 1328
SYNBRANCHIFORMES
Synbranchidae
Symbranchus marmoratus Bloch, 1795	1	0.06	0	0	MZU_PEIXES 1355
Total	1,736	100	990	100

The rarefaction curve (Fig. 3) indicated that natural wetlands had a slightly higher richness of observed and extrapolated species compared to artificial wetlands. Diversity in natural wetlands remained higher along the sampling effort gradient, but the confidence interval overlapped almost completely with the confidence interval of the artificial wetlands. This high overlap indicates that the differences in species richness of both wetland categories are not significant (Tab. 2). Furthermore, both curves showed a tendency to stabilize, which indicates that the sampling effort was sufficient to capture most of the diversity present.

TABLE 2 | Comparison of mean fish diversity metrics in artificial and natural wetlands in the Sinos River floodplain. SD = Standard deviation; p = significance level; art = artificial wetlands, nat = natural wetlands.

	Mean		SD		P
	art	nat	art	nat
Richness	15	12.7	4.289	5.845	0.361
Abundance	289.3	165.0	219.3	104.7	0.238
Shannon	1.78	1.75	0.2446	0.5240	0.907
Equitability	0.74	0.77	0.055	0.0757	0.388

The Tab. 2 shows the mean scores for species richness, abundance, Shannon diversity, and equitability of the fish communities in the artificial and natural wetlands. None of the analysed parameters differed significantly between the two wetland types, confirming the results of the rarefaction.

FIGURE 3| Rarefaction curves of species richness in natural and artificial wetlands in the Sinos River floodplain.

The Fig. 4 shows the linear regression between the relative abundances of the fish species in artificial and natural wetlands (r² = 0.81; P < 0.0001). The ranking of the most abundant fish species in both wetland types is very similar. The most abundant species are Deuterodon luetkenii (20.2% and 18.9%) and Cyphocharax voga (12.2% and 11.3%) in artificial and natural wetlands, followed by Gymnogeophagus gymnogenys (9.5%; 4.3%), Gymnogeophagus rhabdotus (8.3%; 7.5%), Psalidodon fasciatus (7.3%; 8.5%) and Cheirodon ibicuhiensis (6.4%; 9.7%). These most abundant species in both wetland types typically occur in shallow lentic environments.

FIGURE 4| Linear regression of the relative abundances of fish species in artificial and natural wetlands in the Sinos River floodplain.

The Tab. 3 indicates the results of the comparison of principal environmental parameters in artificial and natural wetlands. As for the diversity metrics, environmental parameters dissolved oxygen, conductivity, turbidity and oxidation-reduction potential did not differ significantly between both wetland types.

TABLE 3 | Comparison of the means of environmental variables in artificial and natural wetlands in the Sinos River floodplain. SD = Standard deviation; p = significance level; art = artificial wetlands, nat = natural wetlands.

	Mean		SD		P
	art	nat	art	nat
Dissolved O2 (mg/L)	3.9	4.8	1.349	1.717	0.2960
Conductivity (mS/cm)	0.042	0.054	0.02	0.02	0.3317
Turbidity (NTU)	10.55	13.52	8.384	14.70	0.6760
Oxidation- Reduction Potential (mV)	166.3	149.2	90.00	79.13	0.7110

Discussion​

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The results of our study show that mean fish species richness, abundance, Shannon diversity and equitability did not differ between artificial and natural wetlands in the Sinos River floodplain. The composition of the fish fauna in both wetland types was very similar, with the same species being the most abundant in both categories. The mean equitability scores were 0.74 for artificial and 0.77 for natural wetlands, which means that both wetland types attained 74% and 77% of the maximum possible diversity. These scores indicate a relatively high eveness (Magurran, 1988). As shown for the diversity metrics of the fish community, the means of the environmental parameters dissolved oxygen, conductivity, turbidity and oxygen-reduction potential as well did not differ significantly, showing scores within the expected range for water parameters in wetlands. These results stress the importance of artificial wetlands created by clay extraction, for the conservation of the fish assembly of the Sinos River basin.

The most abundant species in both wetland types were D. luetkenii, C. voga, G. rhabdotus, P. fasciatus, G. gymnogenys, and C. ibicuhiensis. These species share several ecological traits reflecting their common adaptation to southeastern‐South American freshwater habitats. All six typically occur in low‐gradient streams, shallow habitats of coastal lagoons, reservoirs or wetlands, typically in littoral zones with sandy or vegetated substrate, tolerating relatively high temperatures between (≈ 20–28 °C). They are opportunistic omnivores with an insectivorous – detritivorous tendency. Most spawn in warmer months (spring – summer) when temperature and photoperiod peak. All species form loose to dense shoals, especially when juvenile (Reis, Malabarba, 1988; Grosman et al., 1996; Malabarba, 2003; Malabarba et al., 2015; Hirt et al., 2011; Caldatto, 2023).

The loss of natural wetlands is of global concern, considering the services of these ecosystems provide. They control oscillations of the water levels by storing excess water during floods and releasing water during drought, they decrease organic water pollution by decomposing organic sewage, they recharge the ground water tables and are habitat of a diverse aquatic wildlife (De Groot et al., 2018).

The results of our study are similar to the findings of Galatowitsch, Van der Valk (1994), who stated that artificial wetlands can be comparable in structure and functionality to natural wetlands. A study of Gitau et al. (2019) evaluated the recreational, ecological and educational potential of an artificial wetland area derived from clay extraction. Thirteen years after ceasing the commercial activities a long-term monitoring program was initiated and showed the establishment of a high biodiversity, resembling biodiversity levels of natural wetlands of the area. However, other authors came to different conclusions. Almeida et al. (2020) evaluated the functional diversity of plants, birds and fish in different wetlands (natural, restored and constructed) and showed that constructed wetlands do not show the same distribution patterns of flora and fauna as natural wetlands. These different results most probably depend on several factors. Ecological succession, which will lead to a climax with the highest possible diversity takes its time. Therefore, long-term studies probably will find lower differences between artificial and natural wetlands. Improvements during the construction of artificial wetlands may accelerate ecological succession and create favourable conditions for the establishment of a diverse flora and fauna. Meli et al. (2014) state that restoration success of wetlands is context dependent. Factors like ecosystem type, main agent of degradation, restoration action, experimental design and time elapsed since restoration influence the restoration success.

In the case of the Sinos River basin, all sampled wetlands were located in a distance of maximum 600m from the main river channel. Annual river flow usually peaks in the austral winter (June – August; ANA 2024) inundating extended parts of the floodplain. This regular flooding patterns favours fish dispersion from the river into the floodplain and movements of fish between the Sinos main channel and artificial or natural wetlands within floodplain. This seasonal flooding promotes homogenization of faunal distribution. The general assumption that natural ecosystems are characterized by a high diversity of species, which was structured by natural selection on an evolutionary time scale, while anthropogenic systems are formed by a biota with a short evolutionary history and low diversity of species (Primack, Rodrigues, 2006; Agostinho et al., 2008) may not be applied in the Sinos River basin. The cyclic flood pattern most probably causes an annual “ecological reset” of the ecosystem by redistributing the species in the wetlands of the floodplain, independently of their artificial or natural origin.

During the last years, environmental licenses for clay extraction were issued reluctantly by the state´s environmental authority. Our results on fish fauna evidence the clay pits contribute to the conservation of the aquatic diversity and enhance ecosystem services provided by wetlands. Clay extraction areas may partly compensate the wetland losses which occurred during the last decades. The benefits come without financial investment of the state, because the private sector covers the costs, characterizing an ecological-economical win-win situation (Mitsch, Gosselink, 2000). However, the present study is based on a limited survey. Further studies should include longer investigation periods and additional taxonomical groups like macroinvertebrates.

The importance for wetland conservation as retention areas for flood waters cannot be overestimated. During the catastrophical flood events of 2024 in the State of Rio Grande do Sul, 183 people died and another 28 are still missing (Globo, 2024). The financial assessment for the reconstruction of destroyed infrastructure amounts to 110 billion of Brazilian Real (MFAZ, 2024), corresponding approximately U$ 20 billion. In river basins with extended floodplains, the conversion of wetlands in agricultural and urban areas contributes to the extent of the flooding by the elimination of the ecological wetland services related to the absorption of excess water (Barnett, Price, 2010).

In conclusion, artificial and natural wetlands are of great importance in the conservation of biodiversity, being important providers of ecosystem services to the environment and society. The use of artificial wetlands has the capacity to generate new habitats and to shelter many species of fauna and flora, partly making up for the loss of natural ecosystems.

Thus, successful long-term conservation, restoration and management will depend on political priorities that today do not always seek a balance between the economic demands of the agricultural or real estate market and conservation of the ecosystems involved. The clay extraction of the potteries, if organized in a sustainable way, meets the economic demands of the region, contributes to the conservation of aquatic ecosystems and advances in implementing the Sustainable Development Goal 6, which targets integral water resource management for the year 2030 (UNDP, 2025).

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Authors

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Kelly Correia de Lima¹, Caroline dos Santos Brückmann², Ana Caroline Ruppenthal³, Amanda Bauer³, Marlon Ferraz³ and Uwe Horst Schulz³

^[1]    Laboratório de Saneamento, Engenharia Civil, Universidade do Vale do Rio dos Sinos, Avenida Unisinos, 950, Bairro Cristo Rei, 93022-000, São Leopoldo, RS, Brazil. (KCL) kellylima91@hotmail.com.

^[2]    Laboratório de Genética e Biologia Molecular, Universidade do Vale do Rio dos Sinos, Avenida Unisinos, 950, Bairro Cristo Rei, 93022-000, São Leopoldo, RS, Brazil. (CSB) carolbruckmannbio@gmail.com.

^[3]    Laboratório de Ecologia de Peixes, Universidade do Vale do Rio dos Sinos, Avenida Unisinos, 950, Bairro Cristo Rei, 93022-000, São Leopoldo, RS, Brazil (ACR) ana.c.ruppenthal@gmail.com, (AB) amandaleticiabauer@hotmail.com, (MF) ferraz.marlon@outlook.com, (UHS) uwehorstschulz@gmail.com (corresponding author).

Authors’ Contribution

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Kelly Correia de Lima: Formal analysis, Writing-original draft.

Caroline dos Santos Brückmann: Investigation, Visualization.

Ana Caroline Ruppenthal: Investigation, Visualization.

Amanda Bauer: Data curation, Investigation, Methodology.

Marlon Ferraz: Formal analysis, Investigation, Methodology.

Uwe Horst Schulz: Conceptualization, Funding acquisition, Project administration, Supervision, Writing-review and editing.

Ethical Statement​

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The collected fish were euthanized in Eugenol (Lucena et al., 2013) and then fixed in formaldehyde (10%). The collections were licenced by IBAMA (permit number 12430–1) and the Ethic Commission UNISINOS (protocol number PPECEUA06/2014).

Competing Interests

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The author declares no competing interests.

Data availability statement

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The data supporting the findings of this study are available from the corresponding author upon reasonable request.

AI statement

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The authors did not use any AI-assisted technologies in the creation of this manuscript or its figures.

Funding

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The study was partially financed by Petrobras Socioambiental Edital 2012. KCL and AB were supported by internal scholarships of UNISINOS University, CSB and ACR received federal support by CAPES – PROSUC scholarships. We are very grateful for the financial support of these agencies.

Supplementary Material

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Supplementary material S1
Supplementary material S2

How to cite this article

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Lima KC, Brückmann CS, Ruppenthal AC, Bauer A, Ferraz M, Schulz UH. Fish diversity in artificial and natural wetlands in the Sinos River floodplain, Southern Brazil. Neotrop Ichthyol. 2025; 23(4):e250009. https://doi.org/10.1590/1982-0224-2025-0009

Copyright​

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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.

Distributed under

Creative Commons CC-BY 4.0

© 2025 The Authors.

Diversity and Distributions Published by SBI

Accepted November 4, 2025

Submitted January 21, 2025

Epub February 2, 2026