Current and future invasion of a predator with potential for impact negative in a region of high neotropical endemism

Iago V. Geller^1,2 , Jean R. S. Vitule³, João D. Ferraz², Alan D. Pereira⁴ and Mário L. Orsi^1,2

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Abstract​

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Introduction​

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The Neotropical region, which stands out globally for harboring the highest number of plant and animal species (Raven et al., 2020; Palma-Silva et al., 2022), possesses a vast diversity of freshwater fish, with 6.080 described species (Albert et al., 2020), accounting for approximately 30% of the global diversity of this group (Reis et al., 2016; Malabarba, Malabarba, 2020; Larentis et al., 2022; Dagosta et al., 2024).

In the Anthropocene, numerous environmental changes have led to a concerning decline in fish diversity (Isbell et al., 2023; Sayer et al., 2025) driven by climate change, habitat loss, and resource overexploitation (Jaureguiberry et al., 2022; Isbell et al., 2023), with the introduction of non-native species being the primary factor (Jaureguiberry et al., 2022; Milardi et al., 2022; Lipták et al., 2024). The main vectors of these introductions include the ornamental fish trade, aquaculture, biological control, and fish stocking, among others (see review by Bernery et al., 2022). Additionally, numerous political and social initiatives have contributed to this problem by protecting invasive rather than native populations (Vitule et al., 2009; Geller et al., 2020; Franco et al., 2022; Garcia et al., 2022; Pelicice et al., 2023).

The case of the Iguaçu basin, a Neotropical region of high endemism located in southern Brazil, is particularly concerning. This area harbors 133 fish species, distributed across nine orders, 29 families, and 72 genera (Mezzaroba et al., 2021), and has suffered significant biodiversity losses as a result of the introduction of non-native species. (Gubiani et al., 2010; Vitule et al., 2014; Daga et al., 2016; Frota et al., 2022) and inadequate policies (Geller et al., 2020). The basin exhibits approximately 70% endemism (Reis et al., 2020; Mezzaroba et al., 2021), with over 20% of described species listed under some level of threat (ICMBio, 2018; Reis et al., 2020; Mezzaroba et al., 2021; Dagosta et al., 2024; IUCN, 2024), as well as several undescribed species (Reis et al., 2020; Mezzaroba et al., 2021). In contrast, 41 non-native species have been recorded in the basin (Mezzaroba et al., 2021; Frota et al., 2022), including the apex predator Salminus brasiliensis (Cuvier, 1816) (dorado), which has already caused irreversible environmental damage in other regions of Brazil (Alves et al., 2007; Vitule et al., 2014) and poses a severe threat to the endemic ichthyofauna of the Iguaçu River, in addition to potential socio-economic risks for the region (Geller et al., 2021).

The eradication of invasive species is challenging (Bernery et al., 2022; Dechoum, Junqueira, Orsi, 2024), primarily due to difficulties in detecting non-native species at early stages (Hayes et al., 2005). However, early detection significantly increases the likelihood of successful eradication. Among the various tools available for monitoring and detecting non-native species at early stages are citizen science initiatives and online databases (Pawson, Sullivan, Grant, 2020; Geller et al., 2021). Additionally, it is crucial to assess the invasive potential of non-native species in the region, thereby providing valuable information to decision-makers (Early et al., 2016; Shackleton et al., 2019). Predictive modeling approaches can also be utilized to estimate suitable areas for species establishment and assess environmental variables to predict the extent of the expansion of the invasive species (Klippel et al., 2024), further supporting management strategies and eradication efforts.

However, there remains a critical lack of essential data, particularly regarding the number of updated invasion occurrences within a timeframe sufficient to allow real-time monitoring and impact assessment (Bernery et al., 2022). It is believed that the occurrence of S. brasiliensis in the Iguaçu basin has been increasing in recent years and that the species has already adapted to its new habitat, necessitating a detailed evaluation of its invasion processes and future prospects. Therefore, the present study aims to: (i) update the occurrence records of S. brasiliensis in the Iguaçu basin, (ii) analyze the invasiveness level of S. brasiliensis in the Iguaçu basin region and its potential to cause extinctions of endemic fish and (iii) model the current and future distribution of S. brasiliensis in Iguaçu basin and southern Brazil.

Material and methods

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Study area.The Iguaçu River basin covers a region in southern Brazil spanning the states of Paraná (54,820 km²) and Santa Catarina (13,470 km²), encompassing 101 Brazilian municipalities, as well as the province of Misiones in Argentina (1,837.5 km²), with a total area of 70,127.5 km² (Baumgartner et al., 2012). The formation of the Iguaçu River basin dates to the Mesozoic and early Paleozoic Eras and is associated with stepwise uplift movements of the Serra do Mar (Abell et al., 2008), in addition to numerous waterfalls and tributaries along its course (Parolin et al., 2010). The basin is divided into three distinct geomorphological regions: Upper, Middle, and Lower Iguaçu. These subdivisions correspond to the first, second, and third plateau of Paraná, respectively, and serve as important units for the strategic management and utilization of water resources. The three Paraná plateaus comprise: (1) the Curitiba region, (2) the Ponta Grossa region, and (3) the Guarapuava region (Maack, 2002; Baumgartner et al., 2012). The Iguaçu basin is part of the Freshwater Ecoregions of the World (FEOW) of Iguassu (ID 346), classified as tropical and subtropical highland rivers. This ecoregion falls within Gery’s Paranean region and the Paraná-Platense ichthyofaunistic province (Abell et al., 2008; Daga et al., 2016).

Occurrence data.The occurrence data for the development of the current map were obtained through citizen science data from social media platforms, including YouTube®, Facebook®, and Instagram®. The research was based on searches using the following Portuguese keywords: “Pesca do dourado no rio Iguaçu” (dorado fishing in the Iguaçu River), “Pesca de Dourado” (dorado fishing), “Pesca no rio Iguaçu” (Fishing in the Iguaçu River), and “Dourado no rio Iguaçu” (dorado in the Iguaçu River). The citizen science data collection was conducted in January 2025, considering posts made up until December 31, 2024. Videos were accessed in order of availability in the website feed (sorted in descending order based on the number of views). For each video, information was compiled regarding the posting date and the fishing municipality (or a nearby locality). All verified channels, individuals, and accounts, as well as accounts associated with tourism packages, lodging, and advertising, were analyzed separately.Species identification was based on the key morphological characteristics of S. brasiliensis, such as a grayish upper body, a light yellow ventral region with golden coloration, a dark spot on the caudal peduncle extending to the end of the median caudal fin rays a fusiform body shape, and a broad terminal mouth (Graça, Pavanelli, 2007). The identification was further supported by the description of an S. brasiliensis specimen by Gubiani et al. (2010) and expertize of some authors (JRSV and MLO). All photos and videos used in this study were reviewed by experts in the field and are presented in a data table (Tab. S1). Annual records from 2013 to 2024 were analyzed. Pearson’s correlation coefficient (r) was calculated to assess the relationship between year and number of records. Three models were fitted: linear, exponential, and power-law. For the exponential and power-law models, the year was centered (Year – 2012), and parameters were estimated using nonlinear least squares (nls). Model performance was evaluated based on the coefficient of determination (R²), calculated manually for the nonlinear models. All analyses were conducted using R software v. 4.2.2 (R Development Core Team, 2022), with the packages ggplot2, dplyr, and broom.

TABLE 1 | Performance of the MaxEnt Model for Salminus brasiliensis in the La Plata River basin (native) and the of Brazil (invasive): range size (total number of occupied cells and km²), area under the curve (AUC), sensitivity (True Positive Rate – TPR), and specificity (True Negative Rate – TNR) under different scenarios.

Scenario	Occupied cells	Area km²	AUC	Thereshold Kappa (max)	Sensitivity	Specificity
Present day	771646	214.3461	0.839	0.6479	0.8788	0.77.14
RCP 2.6	646109	179.4747	0.898	0.7222	0.8823	0.8421
RCP 4.5	911464	253.1844	0.807	0.591	0.924	0.671
RCP 7.0	662649	184.0692	0.828	0.7222	0.8823	0.8421
RCP 8.5	780999	216.9442	0.822	0.6337	0.8939	0.7428

Aquatic species invasiveness screening kit (AS-ISK).The protocol used was the AS-ISK, which is the new interface (similar) to FISK. It is a generic tool for identifying potentially invasive taxa in aquatic environments, and it is available for download (www.cefas.co.uk/nns/tools). The procedures used in the tool are described in Copp et al., (2016). The AS-ISK consists of 49 questions (Qs) grouped into two main sections, where the biogeographical and historical characteristics of the taxon (13 Qs in total) and its biological and ecological interactions (36 Qs in total) are evaluated, providing the basic risk assessment (BRA). This is complemented by six additional Climate Change Assessment (CCA) questions used to predict how future climatic conditions will likely affect the AS-ISK assessment in relation to the risks of introduction, establishment, spread, and impact, for a total of 55 questions. Each question is answered in classification confidence categories: 1 = low, 2 = medium, 3 = high, 4 = very high. After completing a risk screening, the species receives a BRA score and a BRA+CCA (composite) score, with the scores ranging from -20 to 68 and from -32 to 80, respectively. The BRA+CCA score may increase or decrease by up to 12 points compared to the BRA score but will remain unchanged if the total CCA score is 0.It is important to identify a “threshold” value for the risk assessment (RA) area through a “calibration” process to distinguish between species with medium and high invasiveness risks. Calibration of scores to obtain a threshold is an analytical procedure performed as a subsequent separate step, using the output scores from WRA-type toolkits. Complete descriptions of AS-ISK are available elsewhere (Copp et al., 2016; 2021; Vilizzi et al., 2022). In the end, the tool indicates the confidence scale of the provided state of knowledge: very low (0–0.05), low (0.05–0.33), medium (0.33–0.67), high (0.67–0.95), and very high (0.95–1.00) (Vilizzi et al., 2021). No studies with precise calibration for the RA or proximity were found. Species were classified from the BRA score as low risk (score < 1), medium risk (score between 1–24), or high risk (score > 24) (Dodd et al., 2019; Camargo et al., 2022). To answer the questionnaire, information from scientific journals available on the Web of Science, Google Scholar, and FishBase (http://www.fishbase.org) was used. The resulting spreadsheet for S. brasiliensis in the Iguaçu River basin, as well as the references used for each question, is detailed in the supplementary material.

Dataset.Occurrence records for the modeling of Salminus brasiliensis were obtained from online species databases in zoological collections, including the Centro de Referência em Informação Ambiental (SpeciesLink) and the Global Biodiversity Information Facility (GBIF). Additionally, records collected in the present study through citizen science initiatives, as well as data from scientific publications available on Google Scholar, SciELO, and PubMed (published until December 2024), were included. Only georeferenced records containing precise latitude and longitude coordinates, specimen vouchers, and photographic evidence were considered valid for modeling purposes (Tab. S2).

We adopted the concept of the ecological niche from the perspective of the Grinnellian component, which is determined by abiotic factors such as climate, soil, and altitude, to analyze the potential distribution of S. brasiliensis (Soberón, 2007). To account for the species’ environmental tolerance, we selected six bioclimatic variables as the main predictors of its occurrence: Annual Mean Temperature (BIO1), Max Temperature of the Warmest Month (BIO5), Min Temperature of the Coldest Month (BIO6), Annual Precipitation (BIO12), Precipitation of the Wettest Month (BIO13), and Precipitation of the Driest Month (BIO14). Bioclimatic variables were obtained from WorldClim v. 2.1 (Fick, Hijmans, 2017) (http://www.worldclim.org/). The Representative Concentration Pathways (RCP) were used for modelling future climate predictions for the year 2040, obtained from (http://www.worldclim.org, Fick, Hijmans, 2017). The scenarios based on the Shared Socio-economic Pathways (SSPs) and partly informed by the Representative Concentration Pathways (RCPs), combine baseline socio-economic narratives with different carbon emissions trajectories. There are four SSP-RCP scenarios: RCPs: optimistic (2.6), moderate optimistic (4.5), moderate pessimistic (7.0), and pessimistic (8.5). We follow Ruaro et al., (2019), where the definition of the term ‘‘optimistic’’ means a scenario of low accumulation of greenhouse gases in the Earth’s atmosphere in future, and the term ‘‘pessimistic’’ means a scenario of high accumulation of greenhouse gases. For more information on the RCPs scenarios see Lee et al. (2021). We used the sixth version of the MIROC climatic model 6 (MIROC6) since it includes considerable improvements over previous models (AORI CCSR-NIES 2019; Tatebe et al., 2019).

We performed a Principal Component Analysis (PCA) to reduce redundancy among environmental variables and generate uncorrelated predictors (Peterson et al., 2011). This approach helps minimize collinearity, ensuring that the variables used in the niche model provide independent contributions to species distribution predictions, thereby improving model interpretability and robustness. Since our data consisted of presence-only records, we applied the pseudo-absence technique to generate absence data within the geographical space. This method involves randomly sampling grid cells across the study area to create background points, which are then used to assess the model’s accuracy (Franklin, Miller, 2010). We used the MaxEnt (maximum entropy) algorithm (Phillips et al., 2006) for its high predictive accuracy in modeling species-environment relationships based on presence-only data (Franklin, Miller, 2010). This method is particularly effective in estimating species distributions by identifying the most probable environmental conditions where a species can occur while minimizing assumptions about unknown absence data. Additionally, MaxEnt performs well with limited occurrence records and is robust against spatial sampling bias, making it a widely used tool in ecological niche modeling (Phillips et al., 2006; Elith et al., 2011).

Model calibration and model evaluation.We ran the spatial filter algorithm implemented in the R package (spThin) as proposed by Aiello-Lammens et al. (2019) using a minimum distance parameter of 10 km to reduce a bias towards sites with a high sampling density. This approach allows for controlling the spatial correlation in the occurrence data and is crucial to reduce the effects of uneven or biased occurrence points for a given species (Aiello-Lammens et al., 2019). For ENMs, we used 75% of the occurrence data (N = 153) to calibrate the model and 25% of the occurrence data (N = 51) to validate it. Additionally, 416 background and presence points were used to determine the Maxent distribution.

To assess the ENMs performance, we used widely applied metrics in species distribution modeling: Area Under the Curve (AUC), Sensitivity (True Positive Rate – TPR), Specificity (True Negative Rate – TNR), which is defined as the relative amount of correctly classified absences, and the true skill statistic (TSS) and Maximum Kappa Threshold (Allouche et al., 2006). AUC was chosen for its robustness in evaluating predictive capacity, with values near 1 indicating high discrimination ability (Phillips et al., 2006). Sensitivity assessed the model’s capacity to identify suitable habitats, while specificity ensured non-suitable areas were correctly excluded. Maximum Kappa was used to determine an optimal suitability threshold, measuring agreement between predictions and real data (see Allouche et al., 2006). Maxent jackknife test of variable importance was used to evaluate the relative contribution of each predictor variable to construct the models (Elith et al., 2011).

These metrics were computed for five climate scenarios, including present and future projections under RCP (Representative Concentration Pathways) 2.6, 4.5, 7.0, and 8.5, following IPCC guidelines, enabling comparisons of environmental suitability variations over time. All analyses were conducted using the R software v. 4.2.2 (R Development Core Team 2022;) dismo package (Hijmans et al., 2021).

Results​

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Occurrence of Salminus brasiliensis in the Iguaçu River. A total of 243 individual records (posts) from non-verified accounts documenting the fishing of S. brasiliensis in the Iguaçu River were found, with 154 (63%) of these posts containing information about the specific location, city (in the caption or comments), where the specimen was caught. These records included 85 posts from YouTube®, 53 from Instagram®, and 16 from Facebook®.Two verified commercial Instagram accounts (@eldoradolake and @pousadarecantodoiguaçu) were identified, both of which posted daily about S. brasiliensis fishing in the Iguaçu River. Together, they accounted for more than 350 posts. However, posts lacking location information and those intended for promotional purposes were not considered in this study.

The year 2024 had the highest number of records (73), followed by 2023 (36), 2021 (33), and 2020 (31). A significant positive correlation was observed between the year and number of records (r = 0.88). The linear model explained 77.5% of the variance (R2 = 0.77), while the exponential (R2 = 0.83) and power-law (R2 = 0.81) models showed better fit. The exponential model best captured the recent increase in records, particularly from 2020 to 2024 (Fig. 1).

FIGURE 1| Social media recording of Dorado fishing in the Iguaçu River (2013–2024).

The recorded occurrences were distributed across 15 cities, spanning all three sections of the Iguaçu River (upper, middle, and lower), with 12 cities in the state of Paraná and three in Santa Catarina. The municipality of União da Vitória had the highest number of records (22), followed by Porto Vitória (20), Pinhão (19), Porto Amazonas (17), Mangueirinha (13), Coronel Domingos Soares and Cruz Machado (12), Bituruna and São Mateus do Sul (11), Canoinhas (8), Lapa (4), Balsa Nova (2), and Porto União, São João do Triunfo, and Irineópolis with one record each.

A progressive increase in the number of cities with recorded occurrences was observed over the years. In 2013, S. brasiliensis was recorded in only one city, expanding to four cities by 2015, six in 2016, and nine in 2017. From 2018 to 2021, the number of cities remained stable at 11, increased to 12 in 2022, and reached 15 cities by 2023 and 2024. Notably, of the 17 records found for Porto Amazonas, 16 were from 2024 and one from 2023. Similarly, Lapa and São João do Triunfo only had posts after 2023, indicating a recent presence of the species in the upper Iguaçu region, In Fig. 2, cool colors represent older records, while warm colors indicate more recent ones, revealing an upstream pattern in the river.

FIGURE 2| Map of occurrence of Salminus brasiliensis in the Iguaçu River between the years 2013 and 2024 using citizen science data.

Additionally, numerous records were found in tributaries within the middle section of the Iguaçu River basin, including the Jangada River (PR), Palmital River (PR), Timbó River (SC), and Negro River (SC) (IVG, pers. obs.), not present on the map.

Aquatic Species Invasiveness Screening Kit (AS-ISK) Score. The results obtained from the AS-ISK for S. brasiliensis in the Iguaçu River basin were significant. The Basic Risk Assessment (BRA) score was 38 points, while the BRA+CCA score (Basic Screening+Climate Change Assessment) reached 48 points. The reliability levels obtained in the protocol were: BRA = 0.77, CCA = 0.50, and BRA+CCA = 0.74. These scores indicate a high risk of invasiveness for S. brasiliensis in the Iguaçu River basin, with high reliability, according to the calibration performed for the risk assessment (RA) (Fig. 3; Tab. S3).

FIGURE 3| Invasibility score of the Iguaçu basin for Salminus brasiliensis based on the Aquatic Species Invasiveness Screening Kit (AS-ISK) protocol.

Niche modeling future.Our results suggest that MaxEnt provided robust predictive performance across all scenarios. The AUC values ranged from 0.807 to 0.898, with the highest value observed under the RCP 2.6 scenario (AUC = 0.898), indicating a strong predictive performance. The present-day model achieved an AUC of 0.839, demonstrating reliable accuracy in current climatic conditions. Predictions generated for the present time showed extensive climatically suitable areas for the occurrence of S. brasiliensis in the La Plata River basin and part of the Brazilian territory, resulting in a broad potential distribution of the species, concentrated in the Central-West, Southeastern, and Southern regions of Brazil, as well as in a major part of the La Plata River basin (Tab. 1).

Future climate scenarios indicate variations in species suitability, but without drastic changes. We observed an expansion of the species’ potential range in two distinct scenarios compared to the present (Tab. 2). The RCP 4.5 scenario shows the greatest increase in the area occupied by the species. In contrast, the RCP 2.6 and RCP 7.0 scenarios indicate a reduction in distribution, possibly due to negative environmental impacts. Despite extreme warming, the RCP 8.5 scenario does not lead to a significant decrease in the occupied area. Southern regions, such as the Iguaçu basin and river basins in the state of Santa Catarina, maintain high suitability across all scenarios, aligning with areas where the species is invasive. In contrast, northern areas of the southern region, particularly those near São Paulo and Mato Grosso do Sul states, show lower suitability depending on the climate scenario, corresponding to regions where the species is native (Figs. 4, S4).

TABLE 2 | Estimates of average contribution (% Ct) and permutation importance of the environmental variables (P.I) used in the MaxEnt modeling algorithm for Salminus brasiliensis: present day and projections for 2040 under each Carbon emission scenario.

Variable	Present day		RCP 2.6 2040		RCP 4.5 2040		RCP 7.0 2040		RCP 8.5 2040
	%Ct	P.I	%Ct	P.I	%Ct	P.I	%Ct	P.I	%Ct	P.I
Annual precipitation (BIO 12)	66.9	26	0.4	7.3	0.5	8	0.6	7	0.3	5.9
Precipitation of driest month (BIO 14)	16.7	12	12.2	15.7	11.9	17.9	11.1	14.9	12	17
Annual mean temperature (BIO 1)	7	35.9	1.2	10.1	0.5	7.4	1.1	10.2	0.9	8.6
Max temperature of warmest month (BIO 5)	4.7	3	3.3	3.3	4.7	1.9	3.2	2.3	4.1	2.3
Min temperature of coldest month (BIO 6)	2.4	21.7	70.4	63.5	73	64.2	67.9	63.5	72.1	65.7
Precipitation of wettest month (BIO 13)	2.3	1.3	12.5	0.2	9.4	0.6	16	2.1	10.7	0.5

FIGURE 4| Suitability map for Salminus brasiliensis for future times at different levels of global warming. Current (occurrence native and invasive=scientific+citizen science). Scenario RCP 2.6; RCP 4.5; RCP 7.0 and RCP 8.5. Mesobasins: Ivaí/Piquiri basin (IPB); Ribeira de Iguape basin (RIB); Paranapanema basin (PB); Iguaçu basin (IB) Paraná and Santa Catarina coastal basin (PSCCB); upper Uruguay basin (UUB); middle Uruguay basin (MUB); Jacuí basin (JB); Patos/Mirim basin (PMB).

Jackknife analysis indicated that the Min Temperature of the Coldest Month (BIO 6) was the most influential variable in shaping the distribution of S. brasiliensis across all scenarios, reaching its highest contribution (73%) under RCP 4.5. This underscores the strong dependence of habitat suitability on extreme cold conditions. In the present-day model, Annual Precipitation (BIO 12) was the primary contributing factor (66.9%), but its influence declines considerably in future projections. Meanwhile, Precipitation of the Driest Month (BIO 14) remained consistently relevant, with contributions ranging from 11.1% to 17.9% across different climate scenarios (Tab. 2). These changes indicate that the future distribution of S. brasiliensis may be strongly influenced by minimum temperatures and seasonal variations in precipitation.

Discussion​

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The various combined methodologies applied in this study prove to be relevant for the management, conservation, dispersal, and progression of non-native species. For the Iguaçu basin, this approach has been effective in creating a potential map of the current and future distribution of Salminus brasiliensis, providing insights into the consequences of invasion for local biodiversity, as well as emergency control measures for this invasive species.

Citizen science and the occurrence of S. brasiliensis. Citizen science can track the spread of invasive species, allowing for earlier and more effective eradication, containment, and mitigation measures (Gallo, Waitt, 2011; Pocock et al., 2018; Eritja et al., 2019; Lipták et al., 2024). Citizen science databases rely on community observations and species records, sometimes lacking images. A significant increase in the number of posts about Dorado fishing in the Iguaçu River has been observed in recent years, which can be attributed to several factors. One hypothesis is the widespread availability of smartphones, cameras, and similar devices, combined with the increasing use of digital platforms, which facilitate the documentation and sharing of observations. It is also possible to consider a continuous or even increasing propagule pressure exerted by sport fishing enthusiasts and pseudo-conservationists of the local ichthyofauna, particularly in areas with high human population density and tourism-related enterprises. This growing number of sport fishing practitioners in the region appears to be driven by social media influencers and promotional efforts from fishing lodges and tourism ventures. Additionally, the higher number of posts may reflect a genuine increase in the abundance of Salminus brasiliensis (Dorado) in the Iguaçu River, which would facilitate the capture of individuals and suggest that the species population is continuously expanding and invading new areas. This phenomenon has increasingly attracted sport anglers from outside the region, enhancing its status as a tourist destination. Such a trend is concerning, as these individuals represent the main vectors and propagule sources for species dissemination (Vitule et al., 2014).

However, in citizen science, the number of observations may reflect the level of interest in a species rather than its actual abundance, and the locations of observations may represent the distribution of observers rather than the species itself (Snäll et al., 2011; Giraud et al., 2016). Therefore, the present study aims to demonstrate new records in previously unreported cities and a possible range expansion of the species rather than its abundance. Nonetheless, we support the hypothesis of S. brasiliensis expansion in the Iguaçu basin, highlighting the need for future studies on species abundance in the region.

When analyzing the number of cities where the species is present, a significant increase is observed over the years. The most recent record of S. brasiliensis from citizen science, reported by Geller et al. (2021), extended the known range by 410 km from the first occurrence. Our study updates this expansion by an additional 170 km to the city of Porto Amazonas, indicating the species’ upstream advancement in the Iguaçu River. This was an expected pattern, since the species exhibits migratory behavior, with individuals capable of traveling long distances exceeding 1,000 km (Sverlij, Espinach-Ros, 1986; Agostinho et al., 2003). The cities with the highest posting rates over the past three years are located near Curitiba, the capital of the state of Paraná, which has a population of approximately 1.7 million inhabitants. The combination of easy access to a sport fishing target species and high human population density may have contributed to the increase in reports from local anglers. Additionally, it is important to highlight that large urban centers often act as significant sources of propagule pressure, particularly for symbolic species. In this context, the observed invasion appears to be strongly associated with human activities, especially the recent intensification of sport fishing.

Invasiveness of S. brasiliensis.The Aquatic Species Invasiveness Screening Kit (AS-ISK) is a reliable tool for assessing the invasiveness of non-native fish species. It has been applied to over 120 risk areas worldwide, evaluating 819 non-native species across 15 groups of aquatic organisms, and has proven to be an effective method (Vilizzi et al., 2021). In recent years, its use has increased significantly (see Haubrock et al., 2021; Bakiu et al., 2022; Ge et al., 2024; Lomeu et al., 2024). Based on the AS-ISK assessment protocol and recent occurrence records, S. brasiliensis exhibits a high invasiveness score in the Iguaçu region, posing imminent risks. This highlights the urgent need for control measures, as one of our hypotheses is that the species may have already established a viable population throughout the Iguaçu River basin and is likely expanding into its major tributaries. These tributaries offer suitable environmental conditions for the species, such as the absence of dams, the presence of rapids, and well-oxygenated waters. Finally, further reproductive studies on S. brasiliensis in the region are necessary to better understand the extent and dynamics of its establishment. The Iguaçu River basin is characterized by high endemism due to its unique biogeographical features. The fish species in this region evolved in isolation from the rest of the Paraná system for millions of years following the formation of the Iguaçu Falls during the Cretaceous period (145–65 Ma), which created a natural barrier separating the ichthyofauna upstream from those downstream (Parolin et al., 2010). This geological history is one of the main reasons S. brasiliensis is not native to the region, as natural dispersal upstream of Iguaçu Falls was impossible. The Iguaçu basin hosts 93 native species, with 13 still unclassified (Mezzaroba et al., 2021). Among the 80 documented native taxa, 60 are small-sized species (< 20 cm), 16 are classified as medium-sized (20–40 cm), and only four exceed 40 cm in length (size classification based on Vazzoler, 1996) (see Tab. S5).

According to the IUCN (2025) – Red Data Book of Brazilian Fauna under Threat of Extinction, there are 17 species from the basin at some degree of risk: two species Critically Endangered (CR) – Astyanax eremus Ingenito & Duboc, 2014 and Acrolebias carvalhoi (Myers, 1947); nine species Endangered (EN) – Glandulocauda caerulea Menezes & Weitzman, 2009, Psalidodon gymnogenys (Eigenmann, 1911), Steindachneridion melanodermatum Garavello, 2005, Cambeva crassicaudata (Wosiacki & de Pinna, 2008), Cambeva davisi (Haseman, 1911), Cambeva igobi (Wosiacki & de Pinna, 2008), Cambeva mboycy (Wosiacki & Garavello, 2004), Cambeva papillifera (Wosiacki & Garavello, 2004), Jenynsia diphyes Lucinda, Ghedotti & da Graça, 2006, and Cnesterodon omorgmatos Lucinda & Garavello, 2001; two as Vulnerable (VU) – Astyanax jordanensis Alcaraz, Pavanelli & Bertaco, 2009 and Cnesterodon carnegiei Haseman, 1911; two with insufficient data – Garcialebias araucarianus (Costa, 2014) and Australoheros kaaygua Casciotta, Almirón & Gómez, 2006; and two species considered critically endangered or possibly extinct – Hasemania maxillaris Ellis, 1911 and Hyphessobrycon taurocephalus Ellis, 1911. Only one of these species (S. melanodermatum) is large, meaning that 16 small species are threatened with extinction in the Iguaçu basin (Tab. S5). The assessment of these results is of utmost importance due to the imminent and rapid risk of mass extinction of small-sized species, since the feeding habits of S. brasiliensis predominantly target this type of prey. This species is a top predator in the food chain, preying on fish, insects, crustaceans, small reptiles, and birds in South American aquatic ecosystems (Almeida et al., 1997; Gubiani et al., 2010; Karling et al., 2013). In the upper Paraná region, S. brasiliensis has exhibited high consumption of species such as Steindachnerina insculpta (Fernández-Yépez, 1948), Roeboides descalvadensis Fowler, 1932, Astyanax lacustris (Lütken, 1875), and Piabarchus stramineus (Eigenmann, 1908) (Garcia et al., 2025). A controlled experiment conducted by Santos (2008) on S. brasiliensis revealed a pattern of prey selectivity favoring smaller prey, with a particularly high consumption of Astyanax altiparanae Garutti & Britski, 2000 (current synonymous with A. lacustris), especially following a reduction in prey density.

Additionally, it is important to consider that the fish species of the Iguaçu River basin have evolved in isolation from any actively hunting predators. The natives apex predator in this region, Hoplias aff. malabaricus (Bloch, 1794), H. intermedius (Günther, 1864) and H. misionera Rosso, Mabragaña, González-Castro, Delpiani, Avigliano, Schenone & Díaz de Astarloa, 2016, exhibits an ambush predation strategy, which is fundamentally different from the pursuit hunting behavior of S. brasiliensis. As a result, species in the Iguaçu Basin may exhibit prey naivety (Kovalenko et al., 2010; Martin et al., 2014), displaying weak or even nonexistent antipredator responses (Freeman, Byers, 2006; Smith et al., 2008).

Model the current and future distribution of S. brasiliensis.Climate change will drastically alter the hydrological and thermal characteristics of habitats, as well as the seasonal flow regime, compromising the thermal tolerance of fish (Van Vliet et al., 2013). All climate scenarios indicate variations in the environmental suitability for S. brasiliensis, with the state of Paraná, ecorregion Iguassu (Abell et al., 2008) presenting favorable conditions for its persistence and potential expansion. The results suggest that the future distribution of S. brasiliensis will be strongly influenced by minimum temperatures and variation in seasonal precipitation. With rising minimum temperatures, by 2040 S. brasiliensis may find it even easier to survive winter, increasing its invasiveness in southern Brazil. While the species is losing viability in its native range, it is concurrently expanding into non-native areas, such as the Iguaçu basin.

Moreover, larger-bodied, higher-trophic-level, and migratory fish species tend to increase in abundance at the polar edge while declining at the equatorial edge of their distribution (Brown et al., 2024). This pattern is also observed in the present study for S. brasiliensis, with its potential niche shifting from central Brazil (equatorial region) toward the southernmost regions of the country. The findings of Ruaro et al. (2019) indicate that S. brasiliensis may experience negative alterations in its natural distribution due to climate change, particularly under the most pessimistic scenarios, with climatically suitable areas restricted to the central Paraguay River. This suggests that S. brasiliensis populations are likely to decline across extensive regions of Brazil. However, it is essential to project the species’ potential distribution in non-native environments where it may become invasive. The present study addresses this gap and identifies a vast area of environmental suitability for S. brasiliensis in regions where it is not native, such as the ecorregion Iguassu, Southeastern Mata Atlântica and ecoregion Tramandai-Mampituba.

Using data from our projections for 2040, which incorporate georeferencing in non-native areas, we observed that under all climate change scenarios, particularly the most extreme, there are potential refugia for the species within its natural range, such as the Uruguay River basin (Fig. 4). However, this region has been increasingly impacted by anthropogenic factors, especially river course modifications, contributing to the dorado threatened status (Ribolli et al., 2017). Notably, our projections did not indicate a significant reduction in the overall area of occurrence across Brazil, including both native and non-native regions. In fact, when modeling for invasive areas, we found that the species is expanding into new regions and has a high potential for establishment, particularly in southern Brazil. These analyses are crucial for the early monitoring of affected areas and the management of non-native species.

The species S. brasiliensis has been used as a flagship species in conservation strategies, not only for its own preservation but also for the protection of less charismatic species, through an umbrella strategy (Ruaro et al., 2019; Bailly et al., 2021; Casimiro et al., 2022). In its native range, within the floodplain of the upper Paraná River, the abundance of S. brasiliensis has generally declined over the past 26 years (Dias et al., 2022). Additionally, genetic diversity loss in the Uruguay River threatens the viability of populations isolated by dams (Ribolli et al., 2021). These findings suggest that the species faces a high risk in several areas of its native distribution, with conservation measures proving ineffective. However, recent studies indicate that S. brasiliensis has been recorded in new locations across Brazil as an invasive species. Aguiar-Santos, Meneses (2025) reported its presence in the Preguiça River in the state of Maranhão (Northeast Brazil). Could this emblematic species in its native range become one of Brazil’s main predatory invaders in the near future? Broader studies that consider the roles of climate change and anthropogenic activities in S. brasiliensis invasions across Brazil are still needed. However, our findings in the South highlight the urgent need for species monitoring at the national level. Assessing the consequences of climate change on biodiversity is complex due to uncertainties related to the methods used to obtain responses (Diniz-Filho et al., 2009). Despite predictive uncertainties, ecological niche modeling is essential for conservation, enabling the anticipation of the impacts of climate change on species distributions (Ruaro et al., 2019).

However, biological invasions exhibit several uncertainties and deviate from natural patterns, as seen in the success of a migratory invader in the Iguassu ecoregion. There is an ongoing decline in freshwater fish populations due to climate change (Markovic et al., 2017; Ruaro et al., 2019), with migratory species expected to reduce their range by up to 65% (Bailly et al., 2021). In 2025, the Cherobim Small Hydropower Plant (PCH Cherobim) began operating in Porto Amazonas, with a reservoir covering 1.47 km², including 0.4 km² of river channel and 1.04 km² of newly flooded area (CPFL Energia, 2025). Continuous monitoring of the ichthyofauna is necessary to assess the impacts of this dam on both native and invasive fish species. The migratory behavior of dorado is generally considered a limiting factor for its success, given the habitat challenges at different life history stages and the high mortality rates during migration. However, there are reports of successful invasions by other migratory fish species in South America (Agostinho et al., 2007; Vitule et al., 2012), and the establishment of S. brasiliensis in the Paraíba do Sul and Doce river basins reinforces our concerns, already “prophetically” stated by Ruschi (1965), that the species’ migratory behavior is unlikely to prevent its establishment in other watersheds. Therefore, migratory behavior in aquatic animals alone does not seem to constitute a real barrier to invasion. In particular, once physical barriers are overcome, migratory fish may potentially spread even further than non-migratory species, further suggesting an adaptation to new environments with shorter or absent migrations, which should be evaluated in future studies.

In conclusion, citizen science is an accessible and agile method for collecting large-scale data, facilitating the recording and monitoring of species, in addition to engaging society in conservation and strengthening the protection of biodiversity. We have observed a significant increase in posts of the species Salminus brasiliensis in the Iguaçu basin, moving upstream of the Iguaçu River (> 500 km since the first record), occupying all regions of the basin. The specie high invasiveness (38 points out of 68 possible), with a high confidence rate. The results of the niche modeling of S. brasiliensis demonstrate that climate change may reduce its natural range in central-western Brazil and increase its distribution in invasive areas (Southern Brazil). Although the species is considered an iconic species in South America, for the ecoregion Iguassu it represents a current and future risk to local endemic ichthyofauna, since the main objective of conservation biology is to ensure the long-term maintenance of the greatest number of species Among the recommended strategies for managing and potentially eradicating the species in the region, a key initial measure is the prohibition of catch-and-release practices for S. brasiliensis (dorado) within the Iguaçu River. This should be accompanied by public campaigns promoting the active fishing and removal of the species, as well as outreach initiatives aimed at raising awareness about its negative impacts on smaller endemic species, many of which are threatened with extinction in the Iguaçu basin. Such efforts are essential for fostering an understanding among the general public of the broader implications of invasive species and for highlighting the urgent need to conserve neotropical aquatic biodiversity.

Acknowledgments​

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We would like to thank Dr. James Nienow for his contribution in reviewing the English language and providing guidance on the manuscript. We would like to thank the coordination of Centro Universitário Ugv for the time made available for data analysis. JRSV acknowledges productivity stipend from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, grant number 310471/2023-0).

References​

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Authors

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Iago V. Geller^1,2 , Jean R. S. Vitule³, João D. Ferraz², Alan D. Pereira⁴ and Mário L. Orsi^1,2

^[1]    Programa de Pós-Graduação em Ciências Biológicas, Universidade Estadual de Londrina, Centro de Ciências Biológicas, Rodovia Celso Garcia Cid, PR-445, km 380, 86057-970 Londrina, PR, Brazil. (IVG) iagogeller@hotmail.com (corresponding author).

^[2]    Laboratório de Ecologia de Peixes e Invasões Biológicas (LEPIB) and Laboratório de Ecologia Aquática e Conservação de Espécies Nativas (LEACEN), Universidade Estadual de Londrina, Rodovia Celso Garcia Cid, PR-445, km 380, 86057-970 Londrina, PR, Brazil. (JDF) jd_ferraz@hotmail.com, (MLO) orsi@uel.br.

^[3]    Laboratório de Ecologia e Conservação (LEC), Departamento de Engenharia Ambiental, Universidade Federal do Paraná, Avenida Pref. Lothário Meissner, 632, Jardim Botânico, 80210-170 Curitiba, PR, Brazil. (JRSV) biovitule@gmail.com.

^[4]    Universidade Estadual do Paraná – UNESPAR, campus União da Vitória, Praça Coronel Amazonas, s/nº, Caixa Postal 57, 84600 185 União da Vitória, PR, Brazil. (ADP) alandeivid_bio@live.com.

Authors’ Contribution

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Iago V. Geller: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing-original draft, Writing-review and editing.

Jean R. S. Vitule: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Supervision, Validation, Visualization, Writing-original draft, Writing-review and editing.

João D. Ferraz: Methodology, Validation, Visualization, Writing-original draft, Writing-review and editing.

Alan D. Pereira: Conceptualization, Data curation, Methodology, Software, Supervision, Validation, Visualization, Writing-original draft, Writing-review and editing.

Mário L. Orsi: Conceptualization, Formal analysis, Methodology, Supervision, Writing-review and editing.

Ethical Statement​

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Not applicable.

Competing Interests

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The author declares no competing interests.

How to cite this article

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Geller IV, Vitule JRS, Ferraz JD, Pereira AD, Orsi ML. Current and future invasion of a predator with potential for impact negative in a region of high neotropical endemism. Neotrop Ichthyol. 2025; 23(2):e250056. https://doi.org/10.1590/1982-0224-2025-0056

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 May 2, 2025

Submitted April 1, 2025

Epub August 04, 2025