Stream fish assemblages in the Eastern Amazon: the role of small tetras (Characidae) in alpha diversity and taxonomic structure

Lilian Casatti¹ , Gabriel Lourenço Brejão², Fernando Rogério Carvalho³, Victoria Santos da Costa^1,4, Gabriel Martins da Cruz^5,6, Karina Dias-Silva⁶, Francisco Langeani¹, Maria Dayanne Lima de Lucena^5,6, José Max Barbosa Oliveira-Junior⁷, Thaisa Sala Michelan⁸, Luciano Fogaça de Assis Montag⁶, Beatriz da Cruz Oliveira^1,4, Lidia Brasil Seabra⁶ and Leandro Juen⁶

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Abstract​

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Introduction​

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According to the Living Planet Index by the World Wide Fund for Nature, freshwater ecosystems and biodiversity are considered among the most threatened on the planet, with an average decline of approximately 83% in freshwater organism populations since 1970 (Cooke et al., 2024). Indeed, freshwater biodiversity is disproportionately threatened and underprioritized compared to marine and terrestrial organisms, despite their intrinsic value and the provision of essential ecosystem services (Rees et al., 2021). Harrison et al.(2018) labeled this global phenomenon as “the freshwater biodiversity crisis”. Many of these estimates are based on well-known groups of aquatic vertebrates that have been monitored over decades. However, this situation cannot be applied to Amazonian stream fishes, whose biodiversity is still underestimated, and numerous areas represent spatial gaps that align with the seven shortfalls outlined by Hortal et al. (2015). Consequently, accurately predicting the magnitude of the freshwater biodiversity crisis for Amazonian stream fishes remains challenging.

The Amazon River basin boasts the most diverse regional assemblage of freshwater fishes globally, with 2,716 valid species (1,696 of which are endemic) representing 529 genera, 60 families, and 18 orders (Dagosta, de Pinna, 2019). Since streams harbor approximately 50% of the Amazonian fish fauna (Junk et al., 2007), these water bodies harbor approximately 1,400 species, which stands the Amazon basin as the world’s largest and most biodiverse basin for stream fishes as well (Frederico et al., 2021). As with any other freshwater system, Amazonian stream fishes face multiple threats, including deforestation for agriculture and livestock raising, dam construction, navigable waterway development, urban and mining pollution, and overharvesting for the aquarium trade (Vieira et al., 2008; Castello et al., 2013; Pelicice et al., 2021; Santana et al., 2021).

The shortfalls in knowledge about biodiversity need to be carefully recognized and quantified to make accurate predictions about how it might change in the future (Hortal et al., 2015). This need becomes even more urgent when it comes to megadiverse regions such as the Amazon (Carvalho et al., 2023). To complement the classical descriptors of biodiversity such as composition of species, abundance, species richness, and evenness (Magurran, 2011), there are the taxonomic distinctness indexes, that measure the average degree to which individuals in an assemblage are related to each other and how is the evenness of this relation (Warwick, Clarke, 1995; Clarke, Warwick, 2001; Zintzen et al., 2011).

In the Amazon region, particularly in the Pará State, essential drainages such as Tapajós, Xingu, and Trombetas contribute to the Amazon River and comprise 982, 821, and 494 fish species, respectively (Jézéquel et al., 2020). These drainages encompass the Tapajós-Juruena, Xingu, and Amazonas Guiana Shield ecoregions, respectively (FEOW, 2024). Notably, a large part of these territories contains officially protected areas, in the categories of full protection or sustainable use (MMA, 2024). However, it is important to note that protected networks designed with a focus on terrestrial systems and species are not good enough surrogates to adequately protect the remarkably rich diversity of Amazon stream fishes and these areas are ineffective in safeguarding Amazonian stream fishes (Dagosta et al., 2020; Frederico et al., 2021).

Therefore, this research aims to address knowledge gaps in the taxonomy and distribution of stream fish in the Eastern Amazon, with a particular focus on protected areas in the Pará State. The objectives encompass: (i) describing the ichthyofauna of streams associated with four conservation units in Pará State, (ii) detailing patterns of abundance, richness, diversity, dominance, occurrence, and taxonomic distinctness in each area, and (iii) evaluating the contribution of the present inventory compared to existing records in scientific collections encompassing the ichthyofauna of streams in Pará State.

Material and methods

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Study areas. To conduct this study, a dataset was generated from four field expeditions to the state of Pará within the Amazon biome. The rainy season in this region occurs from December to May, and the dry season from June to November (Moraes, 2005). Because of this, sampling procedures were carried out during the dry periods (of 2021, 2022, and 2023) to avoid the excessive rainfall during the rainy season that may cause changes in the physical and chemical properties of the Amazonian streams and affect the logistics of the sampling procedures (Oliveira-Junior, Juen, 2019). During field expeditions data were systematically collected from 99 streams situated both inside and in the surroundings of the Parque Nacional da Amazônia, Parque Nacional do Jamanxim, Floresta Nacional Saracá-Taquera, and Reserva Biológica Nascentes da Serra do Cachimbo (Tabs. 1, S1; Figs. 1, S2). The selected streams represent diverse types of protected areas from two ecoregions (Tapajós-Xingu and Amazonas Guiana Shield; FEOW, 2024), encompassing a gradient of environmental conditions within and around these designated protected areas or zones.

TABLE 1 | General characteristics of each protected area where fish samples were collected (*from ISA, 2024; **obtained in field).

	Parque Nacional da Amazônia	Parque Nacional do Jamanxim	Floresta Nacional Saracá-Taquera	Reserva Biológica Nascentes da Serra do Cachimbo
Abbreviation	PARNA AM	PARNA JX	FLONA ST	REBIO SC
Status	National Park	National Park	National Forest	National Biological Reserve
Protection category*	Full protection	Full protection	Sustainable use	Full protection
Legal instrument*	Federal Decree nº 73683, of 19/February/1974	Federal Law nº 13425, of 19/June/2017	Federal Decree n° 98704, of 27/December/1989	Federal Decree unnumbered, of 20/May/2005
Area (hectare)*	1,000,000	858,860	429,600	342,478
Phytophysiognomies*	Ombrophilous Dense Forest	Open Ombrophilous Forest and Ombrophilous Dense Forest	Ombrophilous Dense Forest	Ecotone Savannah-Seasonal Forest and Open Ombrophilous Forest
Main drainages	Tapajós	Tapajós	Trombetas	Xingu and Tapajós
Main land use categories	Pasture	Pasture	Mining	Pasture
Sampling period	09–30/November/2021	17/July–08/August/2022	02–26/October/2022	08–29/May/2023
Number of sampled streams	29	28	24	18
Physical and chemical variables (mean ± standard deviation)**
Water temperature (ºC)	25.9 ± 1.1	17.7 ± 4.6	25.5 ± 0.6	24.7 ± 0.9
Conductivity (µS/cm2)	28.3 ± 23.3	23.9 ± 0.9	8.3 ± 1.4	21.7 ± 20.7
Dissolved oxygen (mg/l)	8.9 ± 6.3	4.5 ± 1.1	3.9 ± 0.9	6.1 ± 1.4

FIGURE 1| Sampling sites (indicated by colored symbols) distributed in the protected areas, and characterization of the landscape in the state of Pará, Brazil. AM – Parque Nacional da Amazônia, JX – Parque Nacional do Jamanxim, ST – Floresta Nacional Saracá-Taquera, and SC – Reserva Biológica Nascentes da Serra do Cachimbo.

Fish sampling and identification. In each stream, a 150-meter-long stretch was designated for fish collection. Following the methodology outlined by Prudente et al. (2017), a sampling effort of six hours was allocated for each stream, divided among three to four collectors, who used metal hand nets (55 cm in diameter, 2 mm mesh in opposite nodes) to catch fishes on the bottom, closer to the banks, and in the water column. Collected specimens underwent anesthesia with eugenol, were fixed in 10% formalin, and subsequently preserved in 70% ethanol. Species identification was carried out using specialized taxonomic keys (Géry, 1977; Van der Sleen, Albert, 2018), with identities confirmed by specialists.

Data analysis. Based on the species list compiled, the threatened categories were verified according to the Brazilian Red List (ICMBio, 2022). To complement the first objective and assess the similarity in assemblage structure among areas, a Similarity Analysis (ANOSIM) was conducted with all species of the 99 streams using the Bray-Curtis coefficient (Anderson et al., 2008) and 9,999 permutations, with the areas (PARNA AM, PARNA JX, FLONA ST, REBIO SC) as the grouping factors. ANOSIM is a non-parametric test facilitating the comparison of sample sets (in this case, streams from each area) based on similarity within and between groups (Anderson et al., 2008). The Bray-Curtis coefficient was selected for its appropriateness in handling abundance data (Clarke, Gorley, 2006). Among collected specimens, 35 were juveniles (belonging to the Characidae, Iguanodectidae, Loricariidae, and Rivulidae families), lacking evident diagnostic characters for effective taxonomic determination. Consequently, these juveniles were excluded from quantitative analyses. To visually represent the similarity between streams in a biplot, a non-Metric Multidimensional Scaling Analysis (nMDS) was performed. Both ANOSIM and nMDS analyses were carried out using the PRIMER 6.0 software (Clarke, Gorley, 2006).

For the second objective, the abundance and frequency of occurrence were determined for each species within the set of streams associated with each protected area. Shannon-Wiener diversity in each stream was calculated using the classical formula H’ = – Σ Pi * log Pi , for log base 2, where Pi represents the proportion of species i in each stream (Clarke, Gorley, 2006). Dominance in each stream was assessed using the Berger-Parker index, calculated with the formula d = n / nmax, where n represents the abundance of the most abundant species, and nmax is the total abundance in each stream (Magurran, 2011). The effective number of species, known as Hill numbers or the true diversity for each stream, was also calculated. Hill numbers quantify the number of species in a sample, depending on the common and rare species and incorporate relative abundance and species richness based on the value of the “q” exponent (Chao et al., 2014). Two Hill’s numbers were calculated: q = 0, which is insensitive to the differences in the relative abundances of species, and indicates the effective species richness; q = 1, which includes all species with a weight exactly proportional to their abundance in the community and can be interpreted as the effective diversity (Chao et al., 2014). Diversity indexes were calculated in the PRIMER 6.0 software (Clarke, Gorley, 2006). The species richness estimation for each area was determined by using two nonparametric richness estimators based on sampling coverage (Lee, Chao, 1994), namely ACE (Abundance Coverage Estimator) and ICE (Incidence Coverage Estimator), through the software EstimateS 9.10 (Colwell, 2013). The completeness at each protected area was calculated based on the ratio between observed richness and the total estimated richness obtained by ACE and ICE (Morales-Martínez et al., 2021).

Fish diversity at various taxonomic levels was assessed using two diversity measures: average taxonomic distinctness and variation in taxonomic distinctness (Clarke, Gorley, 2006). Average taxonomic distinctness (also known as Delta+ or AvTD) represents the average taxonomic path length between all pairs of species, indicating whether a species list from a specific locality shares the same taxonomic distinctness structure as the regional pool of species (Clarke, Gorley, 2006). Variation in taxonomic distinctness (also known as Lambda+ or VarTD) is the variance of these pairwise path lengths, reflecting the unevenness of the taxonomic structure in such an assemblage (Clarke, Warwick, 2001). Both Delta+ and Lambda+ are based on an established taxonomic hierarchy into species, genera, families, and orders, known as a master list (Marchant, 2007). For this study, the master list was produced with all species, genera, families, and orders from the 99 streams, while the species list comprises a matrix of species abundance from the four protected area. Both lists were combined in the TAXDTEST routine of the PRIMER 6.0 software (Clarke, Gorley, 2006) to obtain Delta+ and Lambda+ values per stream. Subsequently, these values were plotted against the number of species recorded at each stream, with 95% confidence limits for different numbers of species, resulting in funnel plots. To test whether Delta+ and Lambda+ varied significantly among the four protected areas, a Permutational Multivariate Analysis of Variance (PERMANOVA, Anderson et al., 2008) was performed. This method is suitable for testing data that do not meet the normality assumptions and can utilize any measure of similarity. Among the analysis options, Euclidean distance with 9,999 unrestricted permutations was selected, using the different areas as a fixed factor. These calculations were performed in the PRIMER 6.0 software (Clarke, Gorley, 2006).

To accomplish the third objective, records of freshwater fish in Pará from 11 scientific collections (Tab. S3) available in the SpeciesLink network (CRIA, 2024; accessed on 10/Jan/2024, specieslink.net) and in the ‘Sistema da Informação sobre a Biodiversidade Brasileira’ (SiBBr, 2024; accessed on 12/Jan/2024, https://www.sibbr.gov.br/) were downloaded. The initial data cleaning was based on the following criteria: (i) records from Ostariophysi families that are not typical from streams, according to to Buckup (2021) were removed; (ii) records without geographic coordinates, records from dams or lagoons were removed; (iii) records unidentified at the genus level were removed. After this process, 18,230 records remained. To keep only records from watersheds of similar size to our fish samples, a second round of data cleaning was conducted. To this, watersheds shapefiles for the state of Pará from the HydroSHEDS spatial database (Lehner et al., 2008), at level 10, were obtained. Watersheds larger than 4,300 hectares (the approximate area of the largest basin sampled in the current inventory, see Tab. S1) were excluded from the analysis. This resulted in 2,187 records. Because 38% of this total had undetermined specific epithet (cf., aff., sp.), this comparison was restricted to the generic level, adhering to the validity of generic epithets as outlined in Eschmeyer’s Catalog of Fishes (Fricke et al., 2024a).

Data availability. Fish collection is available in the Species Link system (http://splink.cria.org.br/) and in the TAOCA database (www.taoca.net).

Results​

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In the 99 surveyed streams, a total of 13,602 specimens were collected, belonging to 176 species from 29 families and seven orders (Tab. 2). The small tetras from the Characidae family constituted 33% of all species and 39% of all specimens (Figs. 2, S4). Non-native specimens were not recorded. One threatened species according to the Brazilian Red List was registered: the Vulnerable (VU) Harttia dissidens Rapp Py-Daniel & Oliveira, 2001. This species was represented by three specimens collected in the surroundings of the PARNA JX (site PJF19).

TABLE 2 | Abundance and frequency of occurrence (FO, in %) of each fish species sampled in the 99 stream reaches from Parque Nacional da Amazônia (PARNA AM), Parque Nacional do Jamanxim (PARNA JX), Floresta Nacional Saracá-Taquera (FLONA ST), and Reserva Biológica Nascentes da Serra do Cachimbo (REBIO SC). Unidentified juveniles (n = 35) were not included. Classification follows Fricke et al. (2024a). In bold are the two most abundant species as well as all species with more than 50% of occurrence in each area. Vouchers are deposited in the DZSJRP fish collection at the Departamento de Ciências Biológicas, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista “Júlio de Mesquita Filho”, São José do Rio Preto, São Paulo State, Brazil. *Since there may be several lots of the same species, those with the highest number of specimens and/or largest specimens were reported.

Taxon	Abundance				FO				Voucher DZSJRP*
	PARNA AM	PARNA JX	FLONA ST	REBIO SC	PARNA AM	PARNA JX	FLONA ST	REBIO SC
CHARACIFORMES
Crenuchidae
Ammocryptocharax elegans Weitzman & Kanazawa, 1976	0	24	7	0	0.00	21.43	12.50	0.00	24094
Characidium aff. pteroides Eigenmann, 1909	8	0	0	0	6.90	0.00	0.00	0.00	23691
Characidium aff. zebra Eigenmann, 1909	86	46	0	53	44.83	64.29	0.00	44.44	23451
Characidium sp.	0	0	1	0	0.00	0.00	4.17	0.00	24577
Crenuchus spilurus Günther, 1863	0	0	83	0	0.00	0.00	29.17	0.00	24549
Elachocharax pulcher Myers, 1927	2	0	0	0	3.45	0.00	0.00	0.00	23623
Melanocharacidium cf. dispilomma Buckup, 1993	0	13	0	0	0.00	14.29	0.00	0.00	24256
Microcharacidium bombioides Vieira & Netto-Ferreira, 2021	0	0	102	0	0.00	0.00	50.00	0.00	24530
Microcharacidium sp.	3	675	0	0	3.45	53.57	0.00	0.00	23922
Erythrinidae
Erythrinus erythrinus (Bloch & Schneider, 1801)	50	9	11	0	44.83	17.86	29.17	0.00	23454
Hoplerythrinus unitaeniatus (Spix & Agassiz, 1829)	4	0	0	3	13.79	0.00	0.00	11.11	23512
Hoplias cf. malabaricus (Bloch, 1794)	73	47	2	5	51.72	60.71	8.33	16.67	23459
Cynodontidae
Cynodon septenarius Toledo-Piza, 2000	1	0	0	0	3.45	0.00	0.00	0.00	23601
Anostomidae
Leporinus friderici (Bloch, 1794)	2	0	0	0	6.90	0.00	0.00	0.00	23612
Leporinus cf. gomesi Garavello & Santos, 1981	0	0	0	3	0.00	0.00	0.00	11.11	24719
Leporinus granti Eigenmann, 1912	0	5	0	0	0.00	14.29	0.00	0.00	24189
Curimatidae
Curimatopsis evelynae Géry, 1964	33	0	0	0	6.90	0.00	0.00	0.00	23663
Curimatopsis cf. maculosa Melo, Vari & Oliveira, 2016	0	5	0	0	0.00	3.57	0.00	0.00	23857
Cyphocharax cf. festivus Vari, 1992	0	9	0	0	0.00	7.14	0.00	0.00	24227
Cyphocharax cf. gouldingi Vari, 1992	1	18	0	0	3.45	7.14	0.00	0.00	23988
Lebiasinidae
Copella callolepis (Regan, 1912)	0	0	345	0	0.00	0.00	83.33	0.00	24501
Copella sp.	26	0	0	0	6.90	0.00	0.00	0.00	23599
Nannostomus marginatus Eigenmann, 1909	0	0	22	0	0.00	0.00	20.83	0.00	24507
Pyrrhulina aff. brevis Steindachner, 1876	49	0	836	0	17.24	0.00	91.67	0.00	24518
Pyrrhulina elongata Zarske & Géry, 2001	23	50	0	0	17.24	32.14	0.00	0.00	24040
Pyrrhulina aff. elongata Zarske & Géry, 2001	5	0	0	0	3.45	0.00	0.00	0.00	23517
Pyrrhulina semifasciata Steindachner, 1876	3	0	0	0	3.45	0.00	0.00	0.00	23502
Pyrrhulina sp.	10	0	0	0	3.45	0.00	0.00	0.00	23486
Gasteropelecidae
Carnegiella strigata (Günther, 1864)	62	33	18	0	20.69	28.57	12.50	0.00	23450
Gasteropelecus sternicla (Linnaeus, 1758)	0	10	0	0	0.00	7.14	0.00	0.00	23942
Iguanodectidae
Bryconops cf. affinis (Günther, 1864)	2	0	0	0	3.45	0.00	0.00	0.00	23804
Bryconops inpai Knöppel, Junk & Géry, 1968	0	0	8	0	0.00	0.00	12.50	0.00	24410
Bryconops sapezal Wingert, Chuctaya & Malabarba, 2018	0	1	0	0	0.00	3.57	0.00	0.00	24386
Bryconops sp. 1	7	19	0	0	10.34	14.29	0.00	0.00	23548
Bryconops sp. 2	0	0	6	0	0.00	0.00	8.33	0.00	24479
Iguanodectes cf. purusii (Steindachner, 1908)	0	0	21	0	0.00	0.00	20.83	0.00	24622
Characidae
Amazonichthys lindeae (Géry, 1973)	20	0	0	0	3.45	0.00	0.00	0.00	23746
Aphyocharax sp.	0	1	0	0	0.00	3.57	0.00	0.00	23934
Astyanax aff. bimaculatus (Linnaeus, 1758)	32	70	0	3	31.03	14.29	0.00	16.67	23449
Astyanax moorii (Boulenger, 1892)	1	6	0	0	3.45	3.57	0.00	0.00	24266
Astyanax sp. 1	0	0	0	1	0.00	0.00	0.00	5.56	24768
Astyanax sp. 2	0	0	0	19	0.00	0.00	0.00	33.33	24675
Bario steindachneri (Eigenmann, 1893)	2	0	0	0	3.45	0.00	0.00	0.00	23619
Brachychalcinus reisi Garcia-Ayala, Ohara, Pastana & Benine, 2017	0	0	0	29	0.00	0.00	0.00	16.67	24706
Brachychalcinus signatus Garcia-Ayala & Benine, 2020	0	0	0	3	0.00	0.00	0.00	5.56	24728
Creagrutus ignotus Vari & Harold, 2001	0	5	0	2	0.00	7.14	0.00	5.56	23986
Hemibrycon surinamensis Géry, 1962	7	1	0	0	6.90	3.57	0.00	0.00	23456
Hemigrammus analis Durbin, 1909	0	28	0	0	0.00	28.57	0.00	0.00	23913
Hemigrammus cf. bellottii (Steindachner, 1882)	537	0	29	0	65.52	0.00	20.83	0.00	23625
Hemigrammus cf. geisleri Zarske & Géry, 2007	33	7	0	0	13.79	10.71	0.00	0.00	23626
Hemigrammus melanochrous Fowler, 1913	5	0	0	0	6.90	0.00	0.00	0.00	23696
Hemigrammus cf. ocellifer (Steindachner, 1882)	195	198	0	0	62.07	57.14	0.00	0.00	23458
Hemigrammus cf. rodwayi Durbin, 1909	0	4	0	0	0.00	7.14	0.00	0.00	24315
Hemigrammus cf. schmardae (Steindachner, 1882)	0	0	4	0	0.00	0.00	12.50	0.00	24609
Hemigrammus sp. 1	0	172	0	0	0.00	10.71	0.00	0.00	24210
Hemigrammus sp. 2	4	62	0	0	10.34	21.43	0.00	0.00	23945
Hyphessobrycon aff. cachimbensis Travassos, 1964	0	145	0	0	0.00	3.57	0.00	0.00	24391
Hyphessobrycon copelandi Durbin, 1908	0	231	0	0	0.00	50.00	0.00	0.00	23917
Hyphessobrycon diancistrus Weitzman, 1977	0	3	0	0	0.00	3.57	0.00	0.00	23865
Hyphessobrycon ericae Moreira & Lima, 2017	0	0	27	0	0.00	0.00	12.50	0.00	24542
Hyphessobrycon aff. heterorhabdus (Ulrey, 1894)	206	0	0	0	20.69	0.00	0.00	0.00	23640
Hyphessobrycon peugeoti Ingenito, Lima & Buckup, 2013	4	0	0	0	6.90	0.00	0.00	0.00	23610
Hyphessobrycon cf. peugeoti Ingenito, Lima & Buckup, 2013	1	0	0	0	3.45	0.00	0.00	0.00	23714
Hyphessobrycon cf. pulchripinnis Ahl, 1937	157	0	0	0	37.93	0.00	0.00	0.00	23428
Hyphessobrycon sp. 1	0	1	0	0	0.00	3.57	0.00	0.00	24213
Hyphessobrycon sp. 2	0	0	161	0	0.00	0.00	41.67	0.00	24414
Jupiaba acanthogaster (Eigenmann, 1911)	0	73	0	0	0.00	14.29	0.00	0.00	23991
Jupiaba cf. anterior (Eigenmann, 1908)	0	3	0	2	0.00	7.14	0.00	11.11	24170
Jupiaba anteroides (Géry, 1965)	0	1	0	0	0.00	3.57	0.00	0.00	24032
Jupiaba apenima Zanata, 1997	0	2	0	0	0.00	7.14	0.00	0.00	23921
Jupiaba poranga Zanata, 1997	0	6	0	0	0.00	10.71	0.00	0.00	24063
Knodus cupariensis de Sousa, Silva-Oliveira, Canto & Ribeiro, 2020	99	11	0	0	31.03	7.14	0.00	0.00	23830
Knodus heteresthes (Eigenmann, 1908)	10	21	0	0	13.79	28.57	0.00	0.00	24064
Knodus sp.	24	45	0	524	20.69	25.00	0.00	72.22	24745
Microschemobrycon casiquiare Böhlke, 1953	13	0	0	0	6.90	0.00	0.00	0.00	23831
Microschemobrycon melanotus (Eigenmann, 1912)	0	1	0	0	0.00	3.57	0.00	0.00	23952
Microschemobrycon sp.	1	0	0	0	3.45	0.00	0.00	0.00	23589
Moenkhausia celibela Marinho & Langeani, 2010	45	0	0	0	27.59	0.00	0.00	0.00	23718
Moenkhausia cf. collettii (Steindachner, 1882)	155	0	0	43	62.07	0.00	0.00	22.22	23614
Moenkhausia comma Eigenmann, 1908	110	2	0	0	24.14	3.57	0.00	0.00	23633
Moenkhausia cotinho Eigenmann, 1908	0	1	0	0	0.00	3.57	0.00	0.00	24399
Moenkhausia cf. gracilima Eigenmann, 1908	0	31	0	0	0.00	14.29	0.00	0.00	23993
Moenkhausia lepidura (Kner, 1858)	2	0	0	0	6.90	0.00	0.00	0.00	23465
Moenkhausia aff. melogramma Eigenmann, 1908	39	1,018	0	0	3.45	75.00	0.00	0.00	24222
Moenkhausia mikia Marinho & Langeani, 2010	0	2	0	0	0.00	7.14	0.00	0.00	24218
Moenkhausia oligolepis (Günther, 1864)	33	100	0	3	41.38	64.29	0.00	16.67	23557
Moenkhausia aff. plumbea Sousa, Netto-Ferreira & Birindelli, 2010	1	0	0	0	3.45	0.00	0.00	0.00	23794
Moenkhausia sp.	4	0	0	0	3.45	0.00	0.00	0.00	23674
Phenacogaster cf. calverti (Fowler, 1941)	13	13	0	0	20.69	14.29	0.00	0.00	23593
Phenacogaster cf. ojitata Lucena & Malabarba, 2010	0	0	0	2	0.00	0.00	0.00	5.56	24788
Phenacogaster sp.	1	41	0	1	3.45	39.29	0.00	5.56	24260
Poptella compressa (Günther, 1864)	13	3	0	1	13.79	10.71	0.00	5.56	23676
Rhinopetitia oligolepis Menezes & Netto-Ferreira, 2019	0	3	0	0	0.00	3.57	0.00	0.00	23996
Thayeria boehlkei Weitzman, 1957	0	0	0	1	0.00	0.00	0.00	5.56	24781
Xenurobrycon varii Mendonça, Peixoto, Dutra & Netto-Ferreira, 2016	189	177	0	2	34.48	50.00	0.00	11.11	23468
GYMNOTIFORMES
Apteronotidae
Apteronotus albifrons (Linnaeus, 1766)	1	0	0	0	3.45	0.00	0.00	0.00	23803
Platyurosternarchus macrostoma (Günther, 1870)	0	4	0	0	0.00	7.14	0.00	0.00	24039
Sternopygidae
Eigenmannia aff. trilineata López & Castello, 1966	4	4	0	3	13.79	7.14	0.00	5.56	23941
Sternopygus macrurus (Bloch & Schneider, 1801)	0	1	0	2	0.00	3.57	0.00	11.11	23957
Gymnotidae
Gymnotus coropinae Hoedeman, 1962	3	3	103	1	10.34	3.57	70.83	5.56	23438
Gymnotus aff. carapo Linnaeus, 1758	28	5	3	8	20.69	10.71	12.50	22.22	23807
Gymnotus sp.	1	0	0	0	3.45	0.00	0.00	0.00	23808
Hypopomidae
Brachyhypopomus beebei (Schultz, 1944)	2	7	0	0	6.90	21.43	0.00	0.00	23620
Brachyhypopomus sullivani Crampton, de Santana, Waddell & Lovejoy, 2017	1	49	0	0	3.45	50.00	0.00	0.00	23481
Brachypopomus cf. brevirostris (Steindachner, 1868)	0	0	11	0	0.00	0.00	12.50	0.00	24488
Microsternarchus bilineatus Fernández-Yépez, 1968	1	0	0	0	3.45	0.00	0.00	0.00	23631
Rhamphichthyidae
Gymnorhamphichthys hypostomus Ellis, 1912	1	0	0	0	3.45	0.00	0.00	0.00	23436
Gymnorhamphichthys rondoni (Miranda Ribeiro, 1920)	7	2	9	22	17.24	7.14	20.83	16.67	23437
Hypopygus lepturus Hoedeman, 1962	18	564	3	0	17.24	46.43	12.50	0.00	23552
SILURIFORMES
Cetopsidae
Cetopsis sandrae Vari, Ferraris & de Pinna, 2005	0	1	0	0	0.00	3.57	0.00	0.00	24369
Helogenes marmoratus Günther, 1863	12	6	139	0	20.69	10.71	87.50	0.00	23474
Trichomycteridae
Ammoglanis nheengatu Canto, Hercos & Ribeiro, 2022	85	29	0	0	10.34	10.71	0.00	0.00	23447
Ituglanis amazonicus (Steindachner, 1882)	11	4	1	36	17.24	14.29	4.17	33.33	23485
Callichthyidae
Aspidoras poecilus Nijssen & Isbrücker, 1976	0	1	0	93	0.00	3.57	0.00	22.22	24384
Callichthys callichthys (Linnaeus, 1758)	16	0	2	1	13.79	0.00	8.33	5.56	23637
Hoplisoma benattii (Espíndola, Tencatt, Pupo, Villa‐Verde & Britto, 2018)	1	26	0	0	3.45	14.29	0.00	0.00	24101
Hoplisoma cf. guianense (Nijssen, 1970)	14	109	0	0	10.34	35.71	0.00	0.00	23452
Loricariidae
Ancistrus sp. 1	4	4	0	0	6.90	3.57	0.00	0.00	23617
Ancistrus sp. 2	0	0	0	31	0.00	0.00	0.00	27.78	24755
Ancistrus sp. 3	8	121	0	27	17.24	57.14	0.00	22.22	23570
Farlowella amazonum (Günther, 1864)	8	26	0	0	17.24	21.43	0.00	0.00	23455
Hypostomus soniae Hollanda Carvalho & Weber, 2005	3	28	0	0	3.45	25.00	0.00	0.00	23757
Hypostomus sp. 1	22	18	0	24	13.79	25.00	0.00	27.78	23758
Hypostomus sp. 2	0	2	0	0	0.00	3.57	0.00	0.00	24187
Harttia dissidens Rapp Py-Daniel & Oliveira, 2001	0	3	0	0	0.00	3.57	0.00	0.00	24390
Harttia rondoni Oyakawa, Fichberg & Rapp Py-Daniel, 2018	0	0	0	1	0.00	0.00	0.00	5.56	24658
Curculionichthys itaim Roxo, Dias, Silva & Oliveira, 2017	0	225	0	8	0.00	50.00	0.00	22.22	24102
Curculionichthys sp.	0	11	0	0	0.00	3.57	0.00	0.00	24149
Nannoxyropsis cf. acicula Delapieve, Lehmann A. & Reis, 2018	0	24	0	0	0.00	7.14	0.00	0.00	24105
Otocinclus hasemani Steindachner, 1915	0	20	0	0	0.00	3.57	0.00	0.00	24403
Rhinotocinclus cf. britskii (Boeseman, 1974)	0	2	0	0	0.00	3.57	0.00	0.00	24109
Rhinotocinclus marginalis Reis & Lehmann A., 2022	0	0	0	8	0.00	0.00	0.00	5.56	24697
Rhinotocinclus sp. 1	0	0	0	10	0.00	0.00	0.00	11.11	24721
Rhinotocinclus sp. 2	0	0	0	21	0.00	0.00	0.00	22.22	24722
Rineloricaria cf. hasemani Isbrücker & Nijssen, 1979	0	3	0	0	0.00	7.14	0.00	0.00	24015
Rineloricaria heteroptera Isbrücker & Nijssen, 1976	0	15	0	2	0.00	14.29	0.00	11.11	23979
Rineloricaria lanceolata (Günther, 1868)	0	0	0	1	0.00	0.00	0.00	5.56	24737
Pterygoplichthys scrophus (Cope, 1874)	3	0	0	0	3.45	0.00	0.00	0.00	23818
Aspredinidae
Bunocephalus cf. verrucosus (Walbaum, 1792)	0	10	0	0	0.00	17.86	0.00	0.00	24290
Auchenipteridae
Trachelyopterus galeatus (Linnaeus, 1766)	0	0	0	1	0.00	0.00	0.00	5.56	24753
Tatia intermedia (Steindachner, 1877)	0	0	0	1	0.00	0.00	0.00	5.56	24687
Doradidae
Amblydoras affinis (Kner, 1855)	0	57	0	0	0.00	28.57	0.00	0	23998
Heptapteridae
Cetopsorhamdia sp. 1	0	5	0	8	0.00	7.14	0.00	11.11	24099
Cetopsorhamdia sp. 2	0	0	0	6	0.00	0.00	0.00	5.56	24763
Imparfinis munduruku Castro & Wosiacki, 2019	0	56	0	0	0.00	25.00	0.00	0.00	23971
Imparfinis sp.	0	5	0	5	0.00	7.14	0.00	11.11	24732
New genus (aff. Imparfinis)	0	5	0	0	0.00	3.57	0.00	0.00	24156
Phenacorhamdia sp.	10	16	0	22	13.79	28.57	0.00	33.33	23582
Pimelodella cristata (Müller & Troschel, 1849)	2	0	0	0	3.45	0.00	0.00	0.00	23795
Pimelodella sp.	0	42	0	2	0.00	50.00	0.00	11.11	23956
Rhamdia aff. quelen (Quoy & Gaimard, 1824)	78	2	0	1	27.59	7.14	0.00	5.56	23677
Gladioglanis conquistador Lundberg, Bornbusch & Mago-Leccia, 1991	0	56	0	0	0.00	28.57	0.00	0.00	24077
Nemuroglanis cf. pauciradiatus Ferraris, 1988	0	0	18	0	0.00	0.00	12.50	0.00	24595
Pimelodidae
Pimelodus tetramerus Ribeiro & Lucena, 2006	0	2	0	0	0.00	7.14	0.00	0.00	23877
Pseudopimelodidae
Batrochoglanis villosus (Eigenmann, 1912)	0	1	0	0	0.00	3.57	0.00	0.00	24289
Microglanis sp.	0	178	2	0	0.00	50.00	8.33	0.00	23973
GOBIIFORMES
Eleotridae
Microphilypnus cf. acangaquara Caires & Figueiredo, 2011	3	108	0	0	6.90	21.43	0.00	0.00	23872
SYNBRANCHIFORMES
Synbranchidae
Synbranchus cf. madeirae Rosen & Rumney, 1972	14	18	0	2	20.69	50.00	0.00	11.11	23799
Synbranchus cf. marmoratus Bloch, 1795	2	0	2	0	3.45	0.00	8.33	0.00	24464
CICHLIFORMES
Cichlidae
Aequidens cf. tetramerus (Heckel, 1840)	205	0	64	1	58.62	0.00	50.00	5.56	23673
Aequidens gerciliae Kullander, 1995	0	59	0	0	0.00	25.00	0.00	0.00	24304
Apistogramma agassizii (Steindachner, 1875)	0	0	148	0	0.00	0.00	33.33	0.00	24487
Apistogramma regani Kullander, 1980	0	0	141	0	0.00	0.00	16.67	0.00	24421
Apistogramma sp.	272	583	0	0	58.62	67.86	0.00	0.00	23852
Bujurquina cf. peregrinabunda Kullander, 1986	2	0	0	0	3.45	0.00	0.00	0.00	23704
Bujurquina cf. vittata (Heckel, 1840)	7	0	0	0	10.34	0.00	0.00	0.00	23825
Crenicichla sp. 1	0	0	9	0	0.00	0.00	25.00	0.00	24456
Crenicichla sp. 2	0	0	7	0	0.00	0.00	12.50	0.00	24503
Dicrossus warzeli Römer, Hahn & Vergara, 2010	0	4	0	0	0.00	7.14	0.00	0.00	24122
Mesonauta festivus (Heckel, 1840)	1	0	0	0	3.45	0.00	0.00	0.00	23814
Satanoperca setepele Ota, Deprá, Kullander, Graça & Pavanelli, 2022	10	0	0	0	3.45	0.00	0.00	0.00	23820
Saxatilia aff. lepidota (Heckel, 1840)	7	107	0	8	20.69	67.86	0.00	33.33	23453
CYPRINODONTIFORMES
Rivulidae
Laimosemion dibaphus (Myers, 1927)	0	0	391	0	0.00	0.00	100.00	0.00	24474
Melanorivulus aff. zygonectes (Myers, 1927)	50	0	0	0	10.34	0.00	0.00	0.00	23727
Anablepsoides cf. urophthalmus (Günther, 1866)	107	12	0	0	37.93	17.86	0.00	0.00	23636
Poeciliidae
Poecilia cf. araguaiensis (Costa, 1991)	248	2	0	0	13.79	7.14	0.00	0.00	23729
TOTAL	3,678	6,097	2,736	1,056

FIGURE 2| Some representative species of the Characidae family: lateral view of A. Moenkhausia aff. melogramma,B. Knodus sp., C. Hemigrammus cf. bellottii, D. Hemigrammus cf. ocellifer. E. Lateral and dorsal view of the Vulnerable (VU) armored catfish Harttia dissidens. Photos: Beatriz C. Oliveira.

For occurrence data (Tab. 2), small tetras were present in more than half of the PARNA AM streams, including Hemigrammus cf. bellottii, Moenkhausia cf. collettii, Hemigrammus cf. ocellifer, and the cichlids Apistogramma sp. and Aequidens cf. tetramerus. In the PARNA JX, the group of species occurring in more than half of the streams was more diverse, encompassing Characidium aff. zebra, Hoplias cf. malabaricus, Hemigrammus cf. ocellifer, Moenkhausia aff. melogramma, Moenkhausia oligolepis (Günther, 1864), Ancistrus sp. 3, Apistogramma sp., and Saxatilia aff. lepidota. In the FLONA ST, Copella callolepis (Regan, 1912), Pyrrhulina aff. brevis, Gymnotus coropinae Hoedeman, 1962, Helogenes marmoratus Günther, 1863, and Laimosemion dibaphus (Myers, 1927) were present in over half of the streams. Finally, in REBIO SC, only one undetermined species of Knodus was present in more than half of the sampled streams.

The abundance pattern across the different sets of streams was distinct among the four areas (Tab. 2), but it emphasized the significant presence of small tetras in most cases. The dominant species in the PARNA AM streams were Hemigrammus cf. bellottii and Apistogramma sp.; in the PARNA JX, Moenkhausia aff. melogramma and an undetermined species of Microcharacidium were dominant; in the FLONA ST, the dominant ones were Pyrrhulina aff. brevis and Laimosemion dibaphus; and in REBIO SC, an undetermined species of Knodus and Aspidoras poecilus Nijssen & Isbrücker, 1976 were dominant. ANOSIM identified the structure of fish assemblages in the four areas as different (Global R = 0.715, significance level = 0.01%), as well as the pairwise comparisons (pairwise tests: PARNA AM, PARNA JX, R = 0.417; PARNA AM, FLONA ST, R = 0.825; PARNA AM, REBIO SC, R = 0.6; PARNA JX, FLONA ST: R = 0.938; PARNA JX, REBIO SC, R = 0.547; FLONA ST, REBIO SC: R = 0.871; significance level = 0.01% for all pairwise tests). Indeed, the most dissimilar area corresponds to FLONA ST, which virtually shows no overlap with the other areas (Fig. 3).

FIGURE 3| Biplot resulting from non-Metric Multidimensional Scaling Analysis (nMDS) based on the Bray-Curtis coefficient on all species from 99 streams from Parque Nacional da Amazônia (PARNA AM), Parque Nacional do Jamanxim (PARNA JX), Floresta Nacional Saracá-Taquera (FLONA ST), and Reserva Biológica Nascentes da Serra do Cachimbo (REBIO SC). Points represent streams and are coded according to areas.

The patterns of richness and diversity revealed that, despite sampling a smaller number of streams in REBIO SC — which undoubtedly influenced the species richness in this area — the average richness per stream and indices that describe the diversity were low (Tab. 3). The diversity in REBIO SC streams was impacted by the high dominance of Knodus sp. In contrast, the presence of a large percentage of singletons and unique in this area suggests that there is still a significant portion of local diversity to be documented, as indicated by ACE and ICE (Tab. 3). In contrast, PARNA AM streams had the highest average effective number of species (5.7 for q = 0, Tab. 3) and PARNA JX streams had the highest effective species diversity (4.5 for q = 1, Tab. 3).

TABLE 3 | Fish assemblages’ descriptors derived from 99 stream reaches from Parque Nacional da Amazônia (PARNA AM), Parque Nacional do Jamanxim (PARNA JX), Floresta Nacional Saracá-Taquera (FLONA ST), and Reserva Biológica Nascentes da Serra do Cachimbo (REBIO SC).

Fish assemblages’ descriptors	PARNA AM	PARNA JX	FLONA ST	REBIO SC
Number of records	414	561	244	137
Abundance	3,678	6,097	2,736	1,056
Species richness	90	101	34	48
Number of genera	57	68	30	36
Species richness per stream / min–max[mean]	3–22[14]	2–34[20]	4–17[10]	1–16[7]
Shannon-Wiener diversity / min–max[mean]	1.3–3.9[2.7]	1.0–4.4[3.0]	1.4–3.0[2.2]	0–3.2[1.7]
Berger-Parker dominance / min–max[mean]	0.2–0.9[0.4]	0.1–0.6[0.3]	0.3–0.7[0.5]	0.2–1.0[0.6]
Hill numbers: q = 0 / min–max[mean]	2.5–14.7[5.7]	2.0–21.6[3.9]	2.9–8.1[4.8]	1–9.2[3.2]
q = 1 / min–max[mean]	1.7–11.3[4.1]	2.0–15.9[4.5]	1.9–6.4[3.3]	1–7.2[2.1]
% of singletons (species with only one individual)	15.56	10.89	5.99	25.00
% of uniques (species that occur in one sample)	33.33	24.75	5.99	37.50
Abundance Coverage Estimator (ACE)	101	107	35	60
Completeness based on ACE (%)	89	94	97	80
Incidence Coverage Estimator (ICE)	117	121	35	64
Completeness based on ICE (%)	76	83	97	75
Average distinctness (Delta+)	85.2±5.4	87.6±4.7	92.4±3.7	83.3±22.4
Variation in taxonomic distinctness (Lambda+)	405.1±146.6	342.1±109.7	204.4±90.8	261.4±203.3

The average taxonomic distinctness (Delta+) was notably high in most assemblages, averaging 87.3 and ranging from 0 to 100 (Fig. 4A). This suggests that species are relatively dissimilar from each other in terms of their taxonomic classification, regardless of the protected area. Delta+ values for the studied streams generally fell within the 95% probability funnel, indicating that the fish assemblages exhibited the anticipated level of species diversity for a specific area, with only a few exceptions. Even in assemblages with low richness, Delta+ remained high. Only in the FLONA ST streams, Delta+ was significantly higher than in other areas (Tabs. 3–4). In terms of variation in taxonomic distinctness (Lambda+), the average expected value is 312.5, ranging from 0 to 661.2, and nearly all regions fell within the anticipated limits (Fig. 4B). Interestingly, almost half of the assemblages exhibit a high degree of unevenness concerning their taxonomic structure (Fig. 4B). Among areas, PARNA AM and PARNA JX had the highest values for Lambda+ (Tabs. 3–4).

FIGURE 4| Funnel plots for simulated average taxonomic distinctness (A, Delta+) and variation in taxonomic distinctness (B, Lambda+) from a master species list of 176 taxa samples in 99 streams from Parque Nacional da Amazônia (PARNA AM), Parque Nacional do Jamanxim (PARNA JX), Floresta Nacional Saracá-Taquera (FLONA ST), and Reserva Biológica Nascentes da Serra do Cachimbo (REBIO SC). The 95% probability limits of the simulated values are represented by upper and lower lines of the funnel; the center line of each plot represents the theoretical mean. Points are coded according to protected areas. Observe that FLONA ST is not only the most distinct area (Delta+) but also the most even (Lambda+) regarding the taxonomic arrangement of stream assemblages.

TABLE 4 | Main and pairwise PERMANOVA results based on Euclidean distance, regarding the average taxonomic distinctness (Delta+) and the variation in taxonomic distinctness (Lambda+) of a species master list from 99 streams from Parque Nacional da Amazônia (PARNA AM), Parque Nacional do Jamanxim (PARNA JX), Floresta Nacional Saracá-Taquera (FLONA ST), and Reserva Biológica Nascentes da Serra do Cachimbo (REBIO SC). Bold values are significant.

Main results	Delta+		Lambda+
	Pseudo-F = 3.2897		Pseudo-F = 10.4570
	P(perm) = 0.0065		P(perm) = 0.0001
Pairwise comparisons	t	P(perm)	t	P(perm)
PARNA AM, PARNA JX	17.504	0.0849	18.336	0.0763
PARNA AM, FLONA ST	55.174	0.0001	58.377	0.0001
PARNA AM, REBIO SC	0.4749	0.7616	28.131	0.0063
PARNA JX, FLONA ST	40.693	0.0004	48.786	0.0001
PARNA JX, REBIO SC	10.173	0.3895	17.474	0.0840
FLONA ST, REBIO SC	19.996	0.0063	12.238	0.2299

Overall, 1,333 records (set of species from each stream) were obtained with this inventory, which added 61% to the filtered records from Pará streams (n = 2,187). It is important to mention that these records refer to streams reaches located in watershed up to 4,300 hectares, where 204 genera were registered. The present study added the record of other eight genera, which were not included in the stream records of other collections consulted: Ammoglanis, Apteronotus, Cetopsis, Cetopsorhamdia, Curculionichthys, Hemibrycon, Nannoxyropsis, and Platyurosternarchus. In the collections, the genera Moenkhausia, Hemigrammus, Bryconops, and Hyphessobrycon account for 18% of the records, which is equivalent to that recorded in the present study (20%), reinforcing the relevance of small tetras (Characidae and Iguanodectidae) for Amazonian stream fish diversity (Fig. S5). On the other hand, there are still important spatial gaps in the extreme Northwest and South of the state (Fig. 5), which deserve the direction of new sampling efforts.

FIGURE 5| Spatial coverage of the ichthyofauna of streams in the state of Pará, Brazil, based on data from 11 scientific collections (dark circles, n = 2,187) and those obtained in the present inventory (colored symbols, n = 1,333).

Discussion​

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The fish fauna recorded in this study predominantly comprises small-sized species, defined as those with a standard length of 15 cm or less at adult size (sensu Castro, Polaz, 2020). This group of fish represents the most threatened category, according to the Brazilian Red Book (Castro, Polaz, 2020; ICMBio, 2022). The sole threatened species in this investigation conforms to the small body-size criterion. The rheophilic species Harttia dissidens has been classified as Vulnerable (VU) under criterion A3c due to potential impacts on its natural habitat from hydroelectric power plants and road expansion, which could lead to a population decline of at least 30% over the next decade (Akama et al., 2018). The threatened species was collected outside the boundaries of PARNA JX, underscoring the necessity for surveys within the park to assess viable populations. Additionally, implementing measures such as the protection of riparian buffers is important for minimizing impacts on streams that extend beyond protected areas (Dala-Corte et al., 2020).

Effective species richness and diversity calculated by Hill numbers were the highest in the two largest protected areas (PARNA AM and PARNA JX). Larger protected areas will be more likely to have native forests throughout the longitudinal and lateral dimensions of the stream network, therefore influencing the richness and diversity of species in stream assemblages (see Montag et al., 2018a). When considering the entire set of streams, 24 species were singletons, with most of them being captured inside and in the surroundings of PARNA AM and PARNA JX (Tab. 2). Among these, some species are associated with woody debris and logs (e.g., Tatia intermedia, Trachelyopterus galeatus, Cetopsis sandrae, and Batrochoglanis villosus), while others (e.g., an unidentified Characidium, Harttia rondoni, and Rineloricaria lanceolata) inhabit consolidated bottoms of fast-flowing habitats. As previously noted by other authors, rare species hold disproportionate importance in various aspects of assemblages, including functional structure and co-occurrence patterns (Leitão et al., 2016; Lobato et al., 2022). However, this importance may be severely threatened by the numerous activities and threats occurring in Brazilian Amazon protected areas, notably deforestation (Qin et al., 2023).

The loss of forests both along stream banks and in the watershed leads to well-known and devastating consequences for stream fish fauna (Montag et al., 2018b; Budnick et al., 2019; Dala-Corte et al., 2020), particularly for those species with limited mobility, such as those mentioned herein. This is attributed to a reduction in the presence of allochthonous structures like woody debris and logs, accompanied by an increase in siltation in fast-flowing water areas such as riffles. As a result, habitats become less diverse (Budnick et al., 2019; Zeni et al., 2019), providing fewer opportunities for shelter, feeding, and reproduction of species with limited mobility. Consequently, the survival of these species could be greatly compromised in streams affected by deforestation placing them as strong candidates for being in threat categories of red lists.

In terms of species richness, the importance of the Characidae members in the Amazon basin is well-established, as emphasized by several authors (Lowe-McConnell, 1987; Val, Almeida-Val, 1995; Montag et al., 2018b; Dagosta, de Pinna, 2019). Generally, following Characidae, the families Loricariidae and Cichlidae rank second, with their prevalence alternating based on the availability of suitable habitats, levels of physical degradation, water quality, and biogeographic history. For instance, in different reaches (vegetated habitats and beaches) of the same stream, Montaña et al. (2008) observed that species typically associated with vegetated habitats included small invertivorous cichlids, a small invertivorous doradid catfish, and small characids. On beaches, Montaña et al. (2008) observed that the most common species were small-bodied pelagic characids, indicating the role of instream habitat configuration on the assemblages’ structure. There are cases where biogeographic history, combined with habitat configuration, acts as determining factors, as evidenced by the species recorded in FLONA ST, where the abundant cichlids, lebiasinids, and rivulids were associated with marginal ponds (present study and Silva et al., 2022).

Characidae is the taxonomically most diverse characiform family, representing more than half of the diversity of the order, with 1,236 valid species (Toledo-Piza et al., 2024). Another aspect worth mentioning regarding the Characidae is that its taxonomy is highly dynamic, with 200 species described in just the last decade (2015–2024) (Fricke et al., 2024b) and a significant number of cryptic species that, when studied in greater detail, indicate a highly underestimated species richness of the Amazonian ichthyofauna (Escobar-Camacho et al., 2015; Guimarães et al., 2020). The most rich-species genera of Characidae recorded here, i.e., Hemigrammus, Hyphessobrycon, and Moenkhausia, comprise species with alike ecomorphological traits (Melo et al., 2022), in environments with high rate of diversification in the Neotropical Region, as Eastern of Amazon (Cassemiro et al., 2023). Their small size (cf. Cerezer et al., 2023), low vagility, and similar body shape, combined with the abundance of habitats and resources in the areas, partially account for the significant diversity (and abundance) observed in the studied regions.

The greater proximity between PARNA AM and PARNA JX to REBIO SC has biogeographic implications since these areas are included in the Tapajós-Xingu ecoregions (FEOW, 2024). By contrast, the stream fish fauna of the FLONA ST is not only the most distinct but also the most even regarding the taxonomic arrangement. The FLONA ST is in the Amazonas Guiana Shield ecoregion, specifically in the Trombetas River basin (FEOW, 2024), with an evolutionary history distinct from the other areas. Even though the sampling was quite complete, the total species richness and the richness per stream were low in this basin. However, it is important to highlight that there is a set of species from different families with very conspicuous occurrence, generally associated with stream margins, such as Crenuchus spilurus, Copella callolepis, Pyrrhulina aff. brevis, and Laimosemion dibaphus. Individuals of C. spilurus, e.g., spend most of the day sheltered under shaded areas among structures such as dead leaves and branches, roots, and plants, where they feed on particulate organic matters that sink slowly through the water column during daylight (Pires et al., 2016). For P. aff. brevis, in turn, the individuals move between flooded streamside areas and choose suitable pools while still permitting a swift return to the stream channel if conditions in the flooded area become unfavorable (Espírito-Santo et al., 2017). Therefore, not only can a different evolutionary history explain the results of taxonomic distinctness, but the phylogenetic inheritance needs to be combined with biotic interactions, habitat diversity, and disturbance events that lead to unique taxonomic composition and diversity patterns in these areas that are at the same time cradle and museum of diversity (Melo et al., 2022).

For the variation in taxonomic distinctness, which was particularly high in PARNA AM and in PARNA JX, it is necessary to consider that it represents the success of certain families. This is the case of Characidae, with 31 spp. in PARNA AM and 35 spp. in PARNA JX, contrasting to the four species in FLONA ST and 15 in the REBIO SC. In these two last protected areas, species were more evenly distributed among a wider range of higher taxonomic levels. It is important to note that the number of sampled streams in FLONA ST and in REBIO SC was lower than in other areas, which may affect the uniformity of family representativeness. However, stream fish assemblages in FLONA ST were well characterized, since sampling completeness approached 100%. If the low variation in taxonomic distinctness is influenced by environmental attributes, interactions with other species, or biogeographic and evolutionary history, this should be investigated in future studies. On the other hand, by increasing the number of sites in REBIO SC, there may also be an increase in the variation in taxonomic distinctness, as seen in PARNA AM and PARNA JX, both geographically closer to REBIO SC.

Numerous recent efforts have been made to enhance the understanding of stream fishes in Pará State within protected areas and their surroundings. Freitas et al.(2018), e.g., compiled two decades of studies on fishes in the Caxiuanã National Forest. Rosa et al. (2016), Silva et al.(2016, 2022), Soares et al.(2017), and Barros et al. (2019) investigated ecological aspects of the fishes of the Sacará-Taquera National Forest. Dutra et al. (2020) present a list of 286 fish species documented during a rapid survey of the rivers and streams in the Northern Pará drainage system. This survey encompassed five state protected areas in Pará, namely Faro State Forest, Trombetas State Forest, Paru State Forest, Grão-Pará Ecological Station, and Maicuru Biological Reserve. In these various studies, there is always a recurring theme emphasizing the need for more targeted efforts to address thematic gaps concerning Amazonian fishes, as well as the threats directed towards protected areas. Notably, the present study provides a snapshot of the ichthyofauna, as each locality was sampled only once. Recurrent sampling, coupled with the resolution of many uncertainties in species determination, could enhance richness in the study areas, as Freitas et al.(2018) pointed out in FLONA Caxiuanã. This temporal gap — Prestonian shortfall (Hortal et al., 2015) — in sampling has not been, but needs to be addressed, especially because more robust long-term data about species richness and population dynamics are required to understand how Amazonian biodiversity will respond to climate change (see Borba et al., 2021).

Despite conducting a comprehensive sampling effort across 99 streams, significant spatial gaps persist in the extreme Northwest and South of the state of Pará. These regions are characterized by the presence of indigenous lands, such as Nhamundá-Mapoera, Kaxuyana-Tunayana, and Zo’é in the North, as well as Kapôt Nhinore, Menkragnoti, Kayapó, and Panará in the South (ISA, 2024). Nevertheless, access to and research authorizations within these areas are significantly more restricted. It is important to note that indigenous lands have experienced limited research efforts when compared to strictly protected and sustainable use areas (Carvalho et al., 2023). Only through integrating indigenous lands into a more inclusive scientific approach (Carvalho et al., 2023) can we hope to minimize Wallacean shortfalls, as defined by Hortal et al. (2015).

In summary, the present study highlights the importance of small tetras for the fish fauna of Amazonian streams and emphasizes that, despite substantial efforts in documenting the fish fauna, further spatial and temporal sampling is needed, especially in indigenous territories. Although only one threatened species (the Vulnerable (VU) Harttia dissidens) was recorded, there is a significant portion of this fauna that could be affected in the short term, given its rarity in the areas where it occurs.

Acknowledgments​

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We are grateful to Fundação de Amparo à Pesquisa do Estado de São Paulo and Fundação de Amparo à Pesquisa do Estado do Pará for financial support (FAPESP 2019/25445–1; FAPESPA 068/2020). The Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (process 428961/2018–5) for their support through the project “Diminuindo as lacunas Linneanas e Wallaceanas da biota aquática na Amazônia”. We also acknowledge the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and the Program “Monitora Aquático” for their support and assistance during the collections conducted in the four protected areas in the Eastern Amazon. We immensely thank Angelo R. Manzotti, Antônio A. S. Costa, Bianca C. Barbosa, Clayciane S. Nascimento, Everaldo M. Cordeiro, Everton C. Silva, Geysa K. O. Veloso, Guilherme S. Cabral, Gustavo F. Santos, Josiclaudio P. Freitas, Josinete Monteles, Juan M. R. Pérez, Lorrane G. Cantanhêde, Luiz A. R. Ferreira, Marayerly A. G. Moreno, Mariana A. F. Vieira, Myckey Gonçalves, Rainara Santos, Rafael P. Bastos, Rafael R. Gusmão, Raimundo L. M. Sousa, Tainã S. Rocha, Thiely O. Garcia, and Victor Rennan for their assistance in field data collection. VSC, BCO are students in the Biodiversity Program/UNESP, whereas LBS, MDLL, GMC are students in the Zoology Program/UFPA and receive scholarship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). LC, LFAM, LJ, JMBOJ and FL receive grants from CNPq (LC 304403/2021–0, LFAM 302881/2022–0, LJ 304710/2019–9, JMBOJ 307808/2022-0, FL 313769/2023–0).

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Authors

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Lilian Casatti¹ , Gabriel Lourenço Brejão², Fernando Rogério Carvalho³, Victoria Santos da Costa^1,4, Gabriel Martins da Cruz^5,6, Karina Dias-Silva⁶, Francisco Langeani¹, Maria Dayanne Lima de Lucena^5,6, José Max Barbosa Oliveira-Junior⁷, Thaisa Sala Michelan⁸, Luciano Fogaça de Assis Montag⁶, Beatriz da Cruz Oliveira^1,4, Lidia Brasil Seabra⁶ and Leandro Juen⁶

^[1]    Departamento de Ciências Biológicas, Universidade Estadual Paulista, UNESP, Rua Cristóvão Colombo, 2265, 15054-000 São José do Rio Preto, SP, Brazil. (LC) licasatti@gmail.com (corresponding author), (VSC) victoria.santoss@hotmail.com.br, (FL) francisco.langeani@unesp.br, (BCO) beatriz.cruz@unesp.br.

^[2]    Departamento de Biodiversidade, Universidade Estadual Paulista, UNESP, Avenida 24-A, 1515, 13506-900 Rio Claro, SP, Brazil. (GLB) gabriel.brejao@unesp.br.

^[3]    Laboratório de Ictiologia e Coleção Ictiológica de Três Lagoas (CITL), Câmpus de Três Lagoas (CPTL), Universidade Federal de Mato Grosso do Sul (UFMS), Avenida Ranulpho Marques Leal, 3484, Distrito Industrial II, 79613-000 Três Lagoas, MS, Brazil. (FRC) frcarvalho2004@yahoo.com.br.

^[4]    Programa de Pós-Graduação em Biodiversidade, Universidade Estadual Paulista, UNESP, Rua Cristóvão Colombo, 2265, 15054- 000 São José do Rio Preto, SP, Brazil.

^[5]    Programa de Pós-Graduação em Zoologia, Universidade Federal do Pará, Rua Augusto Corrêa, 01, Guamá, 66075-110 Belém, PA, Brazil.

^[6]    Laboratório de Ecologia e Conservação (LABECO), Instituto de Ciências Biológicas, Universidade Federal do Pará, Rua Augusto Corrêa, 01, Guamá, 66075-110 Belém, PA, Brazil. (GMC) gabrielcruz696963@gmail.com, (KSD) diassilvakarina@gmail.com, (MDLL) maria.daybio@gmail.com, (LFAM) lfamontag@gmail.com, (LBS) Lidia_brasil@yahoo.com, (LJ) leandrojuen@gmail.com.

^[7]    Laboratório de Estudos de Impacto Ambiental (LEIA), Instituto de Ciências e Tecnologia das Águas, Universidade Federal do Oeste do Pará, Rua Vera Paz, 8, Salé, 68040-255 Santarém, PA, Brazil. (JMBOJ) josemaxoliveira@gmail.com.

^[8]    Laboratório de Ecologia de Produtores Primários, Instituto de Ciências Biológicas, Universidade Federal do Pará, Rua Augusto Corrêa, 01, Guamá, 66075-110 Belém, PA, Brazil. (TSM) thaisamichelan@gmail.com.

Authors’ Contribution

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Lilian Casatti: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Writing-original draft, Writing-review and editing.

Gabriel Lourenço Brejão: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Software, Visualization, Writing-original draft, Writing-review and editing.

Fernando Rogério Carvalho: Data curation, Formal analysis, Investigation, Validation, Writing-review and editing.

Victoria Santos da Costa: Data curation, Formal analysis, Methodology, Project administration, Writing-review and editing.

Gabriel Martins da Cruz: Data curation, Methodology, Project administration, Writing-review and editing.

Karina Dias-Silva: Project administration, Writing-review and editing.

Francisco Langeani: Data curation, Investigation, Project administration, Writing-review and editing.

Maria Dayanne Lima de Lucena: Data curation, Methodology, Project administration, Writing-review and editing.

José Max Barbosa Oliveira-Junior: Project administration, Writing-review and editing.

Thaisa Sala Michelan: Project administration, Writing-review and editing.

Luciano Fogaça de Assis Montag: Data curation, Investigation, Methodology, Project administration, Supervision, Writing-review and editing.

Beatriz da Cruz Oliveira: Data curation, Formal analysis, Methodology, Visualization, Writing-review and editing.

Lidia Brasil Seabra: Data curation, Methodology, Project administration, Writing-review and editing.

Leandro Juen: Funding acquisition, Investigation, Methodology, Project administration, Resources, Writing-review and editing.

Ethical Statement​

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Fish collection activities were authorized by the biodiversity authorization and information system (SISBIO under permanent collection license nº 4681-1) and approved by the Ethics Committee (CEUA nº 8293020418, Universidade Federal do Pará).

Competing Interests

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The author declares no competing interests.

How to cite this article

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Casatti L, Brejão GL, Carvalho FR, Costa VS, Cruz GM, Dias-Silva K, Langeani F, Lucena MDL, Oliveira-Junior JMB, Michelan TS, Montag LFA, Oliveira BC, Seabra LB, Juen L. Stream fish assemblages in the Eastern Amazon: the role of small tetras (Characidae) in alpha diversity and taxonomic structure. Neotrop Ichthyol. 2024; 22(3):e240014. https://doi.org/10.1590/1982-0224-2024-0014

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

© 2024 The Authors.

Diversity and Distributions Published by SBI

Accepted August 20, 2024 by Franco Teixeira de Mello

Submitted February 16, 2024

Epub October 18, 2024