Biodiversity Data Journal : Taxonomy & Inventories
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Taxonomy & Inventories
Checklist of the fish fauna of the Munim River Basin, Maranhão, north-eastern Brazil
expand article infoLucas O. Vieira‡,§, Diego S. Campos§,|, Rafael F. Oliveira§,, Josie South#, Marcony S. P. Coelho§, Maurício J. S. Paiva§, Pedro H. N. Bragança¶,¤, Erick C. Guimarães«,»,˄, Axel M. Katz˅, Pâmella S. Brito‡,»,˄, Jadson P. Santos˄, Felipe P. Ottoni‡,§,¶,|
‡ Universidade Federal do Maranhão, Centro de Ciências de Chapadinha, Campus de Chapadinha, Programa de Pós-Graduação em Ciências Ambientais, BR-222, KM 04, Boa Vista, CEP: 65500-000, Chapadinha, Brazil
§ Universidade Federal do Maranhão, Centro de Ciências de Chapadinha, Campus de Chapadinha, Laboratório de Sistemática e Ecologia de Organismos Aquáticos, BR-222, KM 04, S/N, Boa Vista, CEP: 65500-000, Chapadinha, Brazil
| Universidade Federal do Maranhão, Programa de Pós-Graduação em Biodiversidade e Biotecnologia da Amazônia Legal, Av. dos Portugueses, 1966, Cidade Universitária Dom Delgado, 65080-805, São Luís, Brazil
¶ Universidade Federal do Maranhão, Programa de Pós-Graduação em Biodiversidade e Conservação, Av. dos Portugueses, 1966, CEP: 65085-580, São Luís, Brazil
# School of Biology, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
¤ South African Institute for Aquatic Biodiversity, Grahamstown, South Africa
« Universidade Federal do Oeste do Pará, Instituto de Ciências da Educação, Programa de Pós-graduação Sociedade Natureza e Desenvolvimento, Av. Marechal Rondon s/n, CEP: 68040-070, Santarém, PA, Brasil, Belém, Brazil
» Universidade Federal do Maranhão, Departamento de Biologia, Laboratório de Genética e Biologia Molecular, Av. dos Portugueses 1966, Cidade Universitária do Bacanga, CEP: 65080-805, São Luís, Brazil
˄ Universidade Estadual do Maranhão, Laboratório de Ictiofauna e Piscicultura Integrada, Centro de Ciências Agrárias, Campus Paulo VI, avenida Lourenço Vieira da Silva, n. 1000, bairro Jardim São Cristóvão, CEP: 65.055-310, São Luís, Brazil
˅ Universidade Federal do Rio de Janeiro, Laboratório de Sistemática e Evolução de Peixes Teleósteos, Programa de Pós-Graduação em Biodiversidade e Biologia Evolutiva, Instituto de Biologia, CEP: 21.941-902, Rio de Janeiro, Brazil
Open Access

Abstract

Background

The Maranhão State harbours great fish diversity, but some areas are still undersampled or little known, such as the Munim River Basin in the northeast of the State. This lack of knowledge is critical when considering anthropogenic impacts on riverine systems especially in the face of major habitat destruction. These pressing threats mean that a comprehensive understanding of diversity is critical and fish checklists extremely relevant. Therefore, the present study provides a checklist of the fish species found in the Munim River Basin, Maranhão State, north-eastern Brazil, based on collected specimens.

New information

A total of 123 species were recorded for the Munim River Basin, with only two non-native species, Oreochromis niloticus and Colossoma macropomum, showing that the fish assemblage has relatively high ecological integrity. In addition, 29 species could not be identified at the species level, indicating the presence of species that are probably new to science in the Basin. A predominance of species belonging to the fish orders Characiformes and Siluriformes, with Characidae being recovered as the most species-rich family (21 species) agrees with the general pattern for river basins in the Neotropical Region. The total fish diversity was estimated by extensive fieldwork, including several sampling gears, carried out in different seasons (dry and rainy) and exploring different environments with both daily and nocturnal sampling, from the Basin's source to its mouth. A total of 84 sites were sampled between 2010 and 2022, resulting in 12 years of fieldwork. Fish assemblages were distinct in the Estuary and Upper river basin sections and more similar in the Lower and Middle sections indicating environmental filtering processes. Species were weakly nested across basin sections, but unique species were found in each section (per Simpsons Index). High variability of species richness in the Middle river basin section is likely due to microhabitat heterogeneity supporting specialist fish communities.

Keywords

biodiversity, endemism, freshwater, migratory species, taxonomy.

Introduction

The Neotropical Region comprises the most biodiverse freshwater ichthyofauna on the planet, with more than 6000 described species (Reis et al. 2016, Albert et al. 2020). Within the Neotropics, South America harbours the world's greatest diversity of freshwater fishes, including about 5160 described species, which represents about one-third of all known freshwater species (Reis et al. 2016, Pelicice et al. 2017, Castro and Polaz 2020). Studies on diversity of the region have produced estimates which are much higher, predictions being between 8000 to 9000 described and undescribed freshwater fish species (Reis et al. 2016, Birindelli and Sidlauskas 2018, Castro and Polaz 2020, Albert et al. 2020, Koerber et al. 2022). This high diversity is mainly comprised of medium- to small-sized species (species that do not surpass 15 cm standard length), corresponding to 70% of the species (Reis et al. 2003, Castro and Polaz 2020). Small and medium-sized species are broadly distributed throughout all aquatic habitats, which is most likely due to niche partitioning, life history traits adapted to stochastic environments and high trophic plasticity (Vazzoler 1996, Castro 1999, Lowe-Mcconnell 1999, Abelha et al. 2001, Guimarães et al. 2020, Castro and Polaz 2020, Corrêa and Castro 2021). Despite the description of small- and medium-sized fish diversity in scientific journals, they remain largely unnoticed by the general public and neglected by conservation agencies and policies (Castro 1999, Castro et al. 2005, Abell et al. 2011, Albert et al. 2011, Castro and Polaz 2020).

Brazil possesses the highest number of freshwater fish species in South America (Buckup et al. 2007, Castro and Polaz 2020), with about 100 new species being described every year over the last decade (Nelson et al. 2016, Reis et al. 2016, Fricke et al. 2022). However, several of these species represent endemics, with narrow distributions and some are highly threatened due to increased anthropogenic pressure on their natural habitats (Reis et al. 2003, Nogueira et al. 2010, Darwall et al. 2018, Reid et al. 2019). Brazilian freshwaters are subject to multitude anthropogenic threats, such as: deforestation resulting in suppression or reduction of the original vegetation cover, due to logging and expansion of agricultural and urban areas; release of domestic and industrial effluents and chemical products from agricultural activities in aquatic environments, resulting in pollution; irregular water abstraction for different urban, industrial and agricultural uses; soil erosion and silting of the environments; river damming and construction of hydroelectric power plants, disrupting fish migration routes and destroying the natural habitats of fish species; extraction of sand from the riverbeds; mining, resulting in modification of habitats and water pollution and contamination; modification and diversion of the river channels; introduction of non-native species; overharvesting for the aquarium trade; ghost fishing; and overfishing of food fishes (Dudgeon et al. 2006, Pereira et al. 2016, Pelicice et al. 2017, Reid et al. 2019, Zarfl et al. 2019, Zeni et al. 2019, Bergmann et al. 2020, Castro and Polaz 2020, Ottoni et al. 2021, Azevedo-Santos et al. 2021, Doria et al. 2021, Vitorino et al. 2022, Rocha et al. 2023). Despite the high freshwater native fish diversity, non-native fish species have proliferated in Brazil and in Brazilian hydrographic systems where they do not occur naturally due to several human activities, such as: aquaculture, intentional introductions and release, aquarium trade, mosquito larvae biological control interventions, transposition of water between isolated river basins, sport fishing, amongst other activities (Figueredo and Giani 2005, Azevedo-Santos et al. 2011, Vitule et al. 2015, Latini et al. 2016, Padial et al. 2017, Bragança et al. 2020, Doria et al. 2021, Ottoni et al. 2021, Franco et al. 2022, Rocha et al. 2023). Non-native species have caused changes in the local assemblage composition and in the abundance of native species populations, causing major environmental impacts (Giacomini et al. 2011, Latini et al. 2016, Padial et al. 2017, Doria et al. 2021, Ottoni et al. 2021, Rocha et al. 2023).

Maranhão is the westernmost state in north-eastern Brazil, bordered by the Piauí State in the east, from whom it is separated by the Parnaíba River; by Tocantins State in the south and southeast, from which it is separated by the Tocantins River; and by Pará State in the west, from which it is separated by the Gurupi River (Rebêlo et al. 2003). Maranhão total area is about 330000 km2, corresponding to 3.9% of Brazil's territory (Rebêlo et al. 2003, Rios 2005, Batistella et al. 2014, Spinelli-Araújo et al. 2016). Maranhão is an extremely important State in terms of biodiversity, housing three of the main Brazilian biomes, as well as transition areas between them. The Cerrado biome is present in the central, eastern and southern portion of the State; the Amazon biome is present in the western and central portion; and the Caatinga biome is found in the easternmost portion of the State (Rebêlo et al. 2003, Rios 2005, Batistella et al. 2014, Spinelli-Araújo et al. 2016). Thus, Maranhão includes a phytogeographic mosaic due to the presence and overlap of floral elements typical of these three distinct biomes, besides the presence of complex transition areas, making the State extremely biodiverse, ecologically relevant and a key area for conservation (Rebêlo et al. 2003, Rios 2005, Batistella et al. 2014, Spinelli-Araújo et al. 2016).

In the past two decades, several fish surveys were carried out in Maranhão, in both freshwater and estuarine environments, increasing the knowledge of the State's fish fauna (Castro 2001, Castro et al. 2002, Piorski et al. 2003, Pinheiro-Júnior et al. 2005, Soares 2005, Piorski et al. 2007, Castro et al. 2010, Barros et al. 2011, Sousa et al. 2011, Fraga et al. 2012, Almeida et al. 2013, Ribeiro et al. 2014, Ramos et al. 2014, Lima et al. 2015, Matavelli et al. 2015, Melo et al. 2016, Nascimento et al. 2016, Piorski et al. 2017, Brito et al. 2019, Lima et al. 2019, Teixeira et al. 2019, Nunes et al. 2019, Guimarães et al. 2020, Brito et al. 2020, Oliveira et al. 2020, Guimarães et al. 2021c, Guimarães et al. 2021a, Guimarães et al. 2021b). Information about the ichthyofauna of the coastal Munim River Basin, however, is scarce. At the same time, this river basin is under severe anthropogenic pressure from deforestation of marginal vegetation, pollution, contamination of the water, erosion, siltation and even the loss of water bodies (Ribeiro et al. 2006, Ribeiro and Nunes 2017). The Munim River Basin has only five published studies documenting its fish diversity (Ribeiro et al. 2014, Matavelli et al. 2015, Nunes et al. 2019, Oliveira et al. 2020, Guimarães et al. 2021c). These, however, focused on specific localities and environments and, in many cases, surveying only similar and neighbouring sites within this river basin. As a consequence, the fish fauna of the Munim River Basin still awaits a more comprehensive checklist.

The main goal of the present study is to present a detailed inventory of the fish diversity in the Munim River Basin, through the analysis and study of data sampled over 12 years of fieldwork, providing species-level identifications when possible. The study covered the entire river basin and includes relevant information about the importance of checklists in contributing to the knowledge of the river basin, species conservation and distribution. In addition, we provide here ecological and biogeographical comments.

Materials and methods

Study area

Sampling was carried out in rivers, streams, lagoons, swamps, marshes, lakes and the estuary of the Munim River Basin, northeast of the Maranhão State, north-eastern Brazil. The Munim River Basin source is at the Caxias Municipality, in the Cerrado Biome and its mouth is at baía of São José in a region known as "Golfão Maranhense" between the Axixá and Icatu municipalities, within the Cerrado and Amazon biomes (Fig. 1). The Munim River Basin has an area of about 15918.04 km2, with 331.74 km from its source to its mouth (Nugeo 2016, Rios 2005).

Figure 1.  

Map with sampling sites along the Munim River Basin. Sample sites are listed in Table 1 and illustrated on the map as L1-L84. MA = State of Maranhão and PI = State of Piauí. In the highlighted squares are the geographically close sample sites, for better visualisation. River basin sections: Estuary section (green), Lower section (orange), Middle section (lilac) and Upper section (pink).

Sampling sites

Sampling was carried out in 84 collecting sites, covering four different sections of the Munim River Basin, in both rainy (January to May) and dry (June to December) seasons according to Passos et al. (2016). The sampling was done between 2010 and 2022 (about 65% of the surveys were carried out between 2019 and 2022), including sites close to its source and to its mouth (Fig. 1). The sampled environments included rivers, streams, lagoons, swamps, marshes, lakes and the estuary (Table 1, Fig. 2, Suppl. material 1).

Table 1.

Sampling sites at the Munim River Basin, Maranhão, Brazil. *Localities with the presence of non-native species.

Locality number (L)

Locality

Municipality

Coordinates

Altitude

River basin section

01

Stream in the balneário at the entrance of Anapurus

Anapurus - MA

03°40'15.28"S 043°07'9.7"W

81 m

Middle

02

*Stream at balneário São Lourenço

Anapurus - MA

03°39'16.30"S 043°6'50.2"W

75 m

Middle

03

Stream at balneário Recanto do Buriti

Anapurus - MA

03°40'53.04"S 043°7'23.0"W

76 m

Middle

04

Riacho crossing the road at Poços community

Anapurus - MA

03°33'44.61"S 043°3'52.4"W

71 m

Middle

05

Stream at Caraíbas community

Chapadinha - MA

03°56'7.71"S 043°26'14.8"W

51 m

Middle

06

Riacho Xororó at Aparecida neighbourhood

Chapadinha - MA

03°44'2.23"S 043°22'1.21"W

81 m

Middle

07

Stream at Aldeia neighbourhood

Chapadinha - MA

03°45'7.75"S 043°21'32.7"W

74 m

Middle

08

Stream at Aldeia neighbourhood

Chapadinha - MA

03°44'53.1"S 043°21'32.6"W

80 m

Middle

09

Stream at Terra Duras neighbourhood

Chapadinha - MA

03°45'6.42"S 043°22'24.7"W

65 m

Middle

10

Riacho Feio, Boa Vista community

Chapadinha - MA

03°50'51.8"S 043°18'50.5"W

44 m

Middle

11

*Riacho Feio, Boa Vista community

Chapadinha - MA

03°50'46.8"S 043°18'48.9"W

40 m

Middle

12

Riacho Feio, São José community

Chapadinha - MA

03°51'6.30"S 043°17'53.0"W

45 m

Middle

13

*Riacho Feio, São José community

Chapadinha - MA

03°51'18.7"S 043°17'14.4"W

47 m

Middle

14

Riachinho, Cumbre community

Chapadinha - MA

03°51'46.8"S 043°17'10.2"W

52 m

Middle

15

Riachinho, Água Branca community

Chapadinha - MA

03°53'13.5"S 043°16'37.1"W

59 m

Middle

16

Riacho Feio, Riacho Feio community

Chapadinha - MA

03°51'42.84"S 043°16'1.7"W

52 m

Middle

17

Rio Iguará, Malhadinha community

Vargem Grande - MA

03°54'27.8"S 043°44'55.8"W

30 m

Middle

18

Rio Iguará, Malhadinha community

Vargem Grande - MA

03°54'3.25"S 043°44'55.8"W

32 m

Middle

19

Rio Iguará, Poço Cumprido community

Chapadinha - MA

04°2'54.24"S 043°34'58.4"W

41 m

Middle

20

Stream at Itamacaoca forest

Chapadinha - MA

03°44'45.2"S 043°19'15.0"W

90 m

Middle

21

Stream at balneário Repouso do Guerreiro

Chapadinha - MA

03°44'57.4"S 043°20'24.0"W

66 m

Middle

22

Stream at Itamacaoca forest

Chapadinha - MA

03°44'27.2"S 043°19'36.5"W

85 m

Middle

23

Itamacaoca dam

Chapadinha - MA

03°44'56.5"S 043°19'55.8"W

74 m

Middle

24

Stream just after Itamacaoca dam

Chapadinha - MA

03°45'7.42"S 043°20'4.05"W

68 m

Middle

25

Jabuti community, Tinguis road

Chapadinha - MA

03°46'11.9"S 043°20'25.2"W

50 m

Middle

26

Rio Preto at Bom Sucesso community

Mata Roma - MA

03°34'0.40"S 043°19'0.40"W

45 m

Middle

27

Swampy areas at Brejo do Meio community

Chapadinha - MA

03°55'38.7"S 043°30'13.1"W

53 m

Middle

28

Stream behind the Mix Atacarejo Mateus store

Chapadinha - MA

03°45'6.00"S 043°20'23.0"W

59 m

Middle

29

Rio Munim, Carnaúba Amarela community

Chapadinha - MA

03°51'51.3"S 043°19'36.8"W

39 m

Middle

30

Rio Munim, Porções bridge

Chapadinha - MA

03°50'50.0"S 043°19'19.4"W

41 m

Middle

31

*Rio Munim, Cedro community

Chapadinha - MA

03°50'15.5"S 043°19'41.1"W

41 m

Middle

32

Rio Munim, Riacho Fundo community

Chapadinha - MA

03°42'22.7"S 043°31'47.1"W

25 m

Middle

33

Rio Munim, bridge at Mangabeira community

Chapadinha - MA

03°48'34.1"S 043°24'33.2"W

33 m

Middle

34

Stream at Pai Gonçalo community

Chapadinha - MA

04°2'38.12"S 043°28'40.7"W

82 m

Middle

35

Stream at Mucambo community

São Benedito do Rio Preto - MA

03°29'1.01"S 043°33'39.5"W

92 m

Middle

36

Riacho da Raiz

Chapadinha - MA

03°53'45.1"S 043°29'21.3"W

45 m

Middle

37

Riacho São João, São João dos Pilão

Brejo - MA

03°41'2.64"S 042°56'31.9"W

89 m

Middle

38

Riacho Pau Preto, Pau Preto community

Brejo - MA

03°39'54.9"S 042°56'35.5"W

84 m

Middle

39

Riacho da Cruz, close to Palestina

Brejo - MA

03°41'18.0"S 042°58'39.8"W

88 m

Middle

40

Rio Preto, Água Rica community

Brejo - MA

03°41'34.92"S 043°0'56.1"W

78 m

Middle

41

Córrego Água Rica

Anapurus - MA

03°41'41.24"S 043°1'44.8"W

86 m

Middle

42

Riacho do Muquém

Mata Roma - MA

03°42'21.2"S 043°13'57.1"W

68 m

Middle

43

Stream, Laranjeira community

Buriti - MA

03°52'31.09"S 043°3'0.60"W

96 m

Middle

44

Rio Munim, Capoeira Grande community

Afonso Cunha - MA

04°10'2.79"S 043°13'28.0"W

54 m

Upper

45

Rio São Gonçalo

Afonso Cunha - MA

04°7'58.77"S 043°19'16.1"W

64 m

Upper

46

Stream crossing the road

Afonso Cunha - MA

04°10'53.63"S 043°14'1.5"W

58 m

Upper

47

Stream crossing the road

Afonso Cunha - MA

04°12'23.9"S 043°14'46.8"W

68 m

Upper

48

Riacho barrigudinho

Afonso Cunha - MA

04°18'46.1"S 043°13'39.1"W

67 m

Upper

49

Riacho do boi

Afonso Cunha - MA

04°19'12.38"S 043°13'9.8"W

67 m

Upper

50

Stream crossing the road

Aldeias Altas - MA

04°22'14.3"S 043°12'17.6"W

69 m

Upper

51

Riacho do boi

Aldeias Altas - MA

04°26'4.96"S 043°11'46.9"W

82 m

Upper

52

*Rio Bandeira, Belágua

Belágua - MA

03° 9'22.7"S 043°30'35.4"W

65 m

Middle

53

Riacho Água Fria on the road MA-110

Belágua - MA

03°10'9.49"S 043°28'45.3"W

68 m

Middle

54

Rio Bandeira

Urbano Santos - MA

03°11'49.0"S 043°24'29.3"W

41 m

Middle

55

Rio Mocambo

Urbano Santos - MA

03°12'34.6"S 043°24'23.8"W

38 m

Middle

56

Stream on the road MA-224

São Benedito do Rio Preto - MA

03°18'46.2"S 043°30'25.1"W

40 m

Middle

57

Rio Preto, São Benedito do Rio Preto

São Benedito do Rio Preto - MA

03°19'59.0"S 043°31'34.8"W

29 m

Middle

58

Stream on the road MA-224

São Benedito do Rio Preto - MA

03°29'29.0"S 043°35'25.9"W

50 m

Middle

59

Rio Munim, on the road MA-224

Nina Rodrigues - MA

03°35'14.1"S 043°39'50.4"W

21 m

Middle

60

Rio Munim, at the quilombola community Evienã

Presidente Vargas - MA

03°22'31.0"S 043°58'18.5"W

14 m

Middle

61

Riacho Paulica on the road MA-020

Presidente Vargas - MA

03°25'54.98"S 043°58'1.0"W

16 m

Middle

62

Rio Munim at Nina Rodrigues City

Nina Rodrigues - MA

03°27'36.1"S 043°54'15.1"W

14 m

Middle

63

Riacho Paulica on the road BR-222

Vargem Grande -MA

03°31'11.5"S 043°58'30.7"W

23 m

Middle

64

Rio Iguará on the road BR-222

Vargem Grande - MA

03°33'9.64"S 043°52'23.0"W

22 m

Middle

65

Rio Munim mouth at Icatu

Icatu - MA

02°46'33.86"S 044° 4'1.3"W

1 m

Estuary

66

Rio Una, between the municipalities of Morro and Icatu

Morros - MA

02°50'3.06"S 044°2'24.82"W

8 m

Lower

67

Rio das Cobra, Santa Helena community

Morros - MA

02°49'22.1"S 044° 2'34.8"W

9 m

Lower

68

Riacho at the entrance to Icatu

Icatu - MA

02°46'58.50"S 044°2'48.2"W

19 m

Lower

69

Rio Munim, Cachoeira Grande

Cachoeira Grande - MA

02°55'36.25"S 044°3'39.2"W

4 m

Lower

70

Stream crossing the road MA-020

Cachoeira Grande - MA

02°55'14.62"S 044°2'31.5"W

34 m

Lower

71

Stream next to the road MA-402

Axixá - MA

02°51'37.1"S 044° 3'14.5"W

4 m

Lower

72

Rio Munim between the municipalities of Axixá and Presidente Juscelino

Axixá - MA

02°52'35.63"S 044°3'41.8"W

15 m

Lower

73

Stream between the municipalities of Axixá and Presidente Juscelino

Axixá - MA

02°53'50.06"S 044°4'15.9"W

4 m

Lower

74

Rio Munim, Presidente Juscelino

Presidente Juscelino - MA

02°55'39.38"S 044°3'50.5"W

6 m

Lower

75

Rio Una, Cachoeira do Arruda

Morros - MA

02°53'31.5"S 043°58'13.8"W

28 m

Lower

76

Riacho das Pacas

Morros - MA

02°51'4.94"S 043°57'52.1"W

28 m

Lower

77

Stream next to the road MA-402

Morros - MA

02°51'19.5''S 044°01'03.0''W

19 m

Lower

78

Rio Munim, Axixá

Axixá - MA

02°50'14.60"S 044°3'3.81"W

1 m

Lower

79

Rio Munim, Balceiro community

Chapadinha - MA

03°46'44.9"S 043°26'42.7"W

33 m

Middle

80

Stream at the Paiol community

Chapadinha - MA

04°1'13.56"S 043°29'27.6"W

74 m

Middle

81

Stream at São Pedro community

Chapadinha - MA

03°54'4.66"S 043°35'12.3"W

73 m

Middle

82

Stream crossing a road in the Resex

Chapadinha - MA

03°56'10.0"S 043°30'29.5"W

61 m

Middle

83

Riacho Xororó at Aparecida neighbourhood

Chapadinha - MA

03°44'7.77"S 043°22'8.94"W

69 m

Middle

84

Riachinho, Água Branca community

Chapadinha - MA

03°52'37.67"S 043°16'59.37"W

60 m

Middle

Figure 2.  

Samples sites: L1, L18, L19, L30, L31, L36, L38, L43, L49, L53, L54, L55, L62, L65, L66, L69, L75, L77, L78 and L84 according to Table 1. Photographed by Lucas Vieira and Rafael Oliveira, edited by Axel Katz.

Sampling and specimens identification

All (about 160) sampling events were carried under the permits issued by Instituto Chico Mendes de Conservação da Biodiversidade (ICMBIO; License nº 54949, 57258, 57787, 64415, 73267). In addition, material already housed at the Coleção Ictiológica do Centro de Ciências Agrárias e Ambientais (CICCAA) of the Universidade Federal do Maranhão, was also used in this study. The specimens were sampled by using different sampling gear, such as fishing line, hand net, seine net, cast net, gill nets and crayfish-type traps (Souza and Auricchio 2002). All the sampling activities and procedures followed the best practices and standards for animal welfare as presented in Leary et al. (2020). Specimens were euthanised by immersion in a 250 mg/l Tricaine methane sulphonate (MS-222) solution until the cessation of opercular movements.

Following the euthanasia, the specimens for morphological studies were preserved in formalin (10%) and moved to a 70% ethanol solution after 10-15 days. Specimens selected for future molecular studies were preserved in 99% ethanol. The processing and identification of specimens were made at the Laboratório de Sistemática e Ecologia de Organismos Aquáticos (LASEOA), at the Universidade Federal do Maranhão, by the use of specialised bibliography for each taxonomic group and by consulting specialists. The specimens were identified to the lowest taxonomic rank possible. All biological material is catalogued and housed at the Coleção Ictiológica do Centro de Ciências Agrárias e Ambientais (CICCAA) of the Universidade Federal do Maranhão (UFMA) (Suppl. materials 1, 2). The taxonomic classifications, species names, authorship and year, original descriptions, habitat of occurrence and geographic distributions were verified and presented according to Fricke et al. (2022a), Fricke et al. (2022b) and Froese and Pauly (2022).

Map and Munin River Basin sections distinction

The geographic coordinates of each collection site along the Munim River Basin were registered from a GPS device and then converted to the shapefile format, with place names and respective codes in the attribute table. Additional data on boundaries from river basins and political division of territory were acquired from the official data service IBGE (Brazilian Institute for Geography and Statistics). The map was composed in QGIS 3.22.12 (Qgis development team 2022). Due to scale, each point on the map may correspond to one or more collection sites, depending on the geographic proximity.

The Munim River Basin was divided into four sections: Estuary section with an area of 78.89 km2, comprising one collecting site; Lower river basin section with an area of 2891.89 km2, comprising 13 collecting sites; Middle river basin section with an area of 10722.29 km2, comprising 62 collecting sites; and Upper river basin section with an area of 2224.90 km2, comprising eight collecting sites (Fig. 1, Table 1, Suppl. material 2). The criterion for the sectorisation of the basin was based on the average slope calculated from the elevation values (meters above sea level) of the digital elevation model SRTM/USGS, available at the TOPODATA/INPE project (http://www.dsr.inpe.br/topodata/). Based on the analysed area, this river basin varies from 0 to 162 meters above the sea level. The parameters considered for the sectorisation were: Estuary section - average slope of 1.09 (standard deviation 1.59); Lower river basin section - average slope of 1.41 (standard deviation 1.33); Middle river basin section - average slope of 2.63 (standard deviation: 2.43); and Upper river basin section - average slope of 3.11 (standard deviation 2.61) (Fig. 1, Table 1, Suppl. material 2).

Species photographs

Specimens of some species were photographed in the laboratory to illustrate the diversity of species that occur in the Munim River Basin (Fig. 3, Fig. 4 and Fig. 5). Additional photographs of Munim River fish species can be seen in Guimarães et al. (2018b): figs. 1, 2, Oliveira et al. (2020): fig. 3, Guimarães et al. (2021c) and Aguiar et al. (2022): fig.2b.

Figure 3.  

Selected fish species collected in the Munim River Basin of the Order Characiformes: A Acestrorhynchus falcatus (CICCAA 06398, 112.60 mm SL), B Aphyocharax sp. (CICCAA 06636, 32.91 mm SL), C Charax awa (CICCAA 06430, 80.22 mm SL), D Gasteropelecus sternicla (CICCAA 06366, 39.50 mm SL), E Hemiodus parnaguae (CICCAA 06238, 94.99 mm SL), F Leporinus aff. friderici (CICCAA 02755, 102.31 mm SL), G Metynnis lippincottianus (CICCAA 06383, 64.06 mm SL), H Moenkhausia cf. intermedia (CICCAA 06634, 50.38 mm SL), I Moenkhausia sp. (CICCAA 06635, 35.10 mm SL), J Poptella compressa (CICCAA 06429, 42.46 mm SL), K Prochilodus lacustris (CICCAA 06340, 84.94 mm SL), L Psectrogaster rhomboides (CICCAA 06270, 121.08 mm SL), M Pygocentrus nattereri (CICCAA 06271, 138.08 mm SL), N Schizodon dissimilis (CICCAA 06344, 99.03 mm SL), O Serrasalmus rhombeus (CICCAA 06269, 70.99 mm SL), P Triportheus signatus (CICCAA 06339, 86.62 mm SL). Photographed by Lucas Vieira and Rafael Oliveira, edited by Axel Katz.

Figure 4.  

Selected fish species collected in the Munim River Basin of the Order Siluriformes: A Ancistrus sp. (CICCAA 06652, 76.85 mm SL), B Auchenipterus menezesi (CICCAA 06534, 98.38 mm SL), C Batrochoglanis sp. (CICCAA 06654, 64.16 mm SL), D - Callichthys callichthys (CICCAA 03927, 102.12 mm SL), E Corydoras julii (CICCAA 06378, 34.33 mm SL), F Corydoras vittatus (CICCAA 06418, 34.19 mm SL), G Hassar affinis (CICCAA 06263, 109.79 mm SL), H Hoplosternum littorale (CICCAA 06657, 81.91 mm SL), I Hypoptopoma incognitum (CICCAA 06315, 70.81 mm SL), J Ituglanis cf. amazonicus (CICCAA 06643, 30.53 mm SL), K Loricaria cf. cataphracta (CICCAA 06628, 105.80 mm SL), L Loricariichthys sp. (CICCAA 06328, 160.18 mm SL), M Pimelodella sp.1 (CICCAA 06629, 83.02 mm SL), N Platydoras brachylecis (CICCAA 04608, 58.36 mm SL), O Pseudoplatystoma fasciatum (CICCAA 04549, 208.39 mm SL), P Sorubim lima (CICCAA 06272, 204.01 mm SL), Q Tatia intermedia (CICCAA 02736, 46.17 mm SL), R Trachelyopterus galeatus (CICCAA 06243, 122.56 mm SL). Photographed by Lucas Vieira and Rafael Oliveira, edited by Axel Katz.

Figure 5.  

Selected fish species collected in the Munim River Basin of the Orders Cichliformes and Gymnotiformes: A Geophagus parnaibae (CICCAA 06229, 98.62 mm SL), B Satanoperca jurupari (CICCAA 06377, 105.36 mm SL), C Apteronotus albifrons (CICCAA 06266, 168.59 mm TL), D Eigenmannia robsoni (CICCAA 06631, 180.36 mm TL), E Sternopygus macrurus (CICCAA 06261, 183.50 mm TL). Photographed by Lucas Vieira and Rafael Oliveira, edited by Axel Katz.

Migratory species

Species were classified as migratory based on Carolsfeld et al. (2003). When any species was not listed in Carolsfeld et al. (2003), we considered the genus to indicate if it is a migratory species.

General species accumulation curve

A matrix of occurrence and abundance data over the sampling period, for this study, was used to plot the general species accumulation curve with Primer-e statistical software (Clarke and Gorley 2006), based on a spreadsheet containing relevant data for this analysis (Suppl. material 2). Given that the order of samples in the analysis affects the shape of the curve produced, due to heterogeneity amongst the species in the samples (Ugland et al. 2003), 1000 permutations were calculated to overcome this effect.

Species Richness and Fish assemblage composition

The statistical and ecological analyses were based on a spreadsheet containing relevant data for these analyses (Suppl. material 2).

Species Richness

Species richness (Sprich) (i.e. number of species in each river basin section) was compared using Kruskal-Wallis tests, on account of non-normal distribution (per Shapiro-Wilk test) and Dunn post-hocs with Holm adjusted p-values to account for multiple comparisons were used to determine section level differences. Visualisation was completed through the R package '“ggstatsplot'” (Patil 2021).

Fish assemblage composition

Fish assemblage composition was compared between basin sections, at the basin section level, using presence-absence data due to surveys not being standardised for sampling methods. Only native species were included in the analysis. First, nestedness was assessed using the NODF method (Almeida-Neto et al. 2008), which is bound between 0 and 100 where 100 is perfect nestedness, via vegan::nestednodf, then Sørensen dissimilarity and Simpsons Index were calculated using vegan::nestedbetasor. Sørensen dissimilarity closer to 0 indicates more shared species. Simpsons Index is not affected by species richness and represents true turnover, i.e. the the replacement of some species by other species from section to section, independent of potential differences in species richness between the sections. Areas with Simpsons Index values over 66% are considered to have similar faunal composition (Sánchez and López 1988). Jaccard Index was calculated using vegan::nestedbetajac where values closer to one indicate higher similarity. A cluster analysis and dendrogram was completed on the section Jaccard coefficients using the Ward.D2 method. All statistical analyses were performed within the R software environment version 4.0.2 and the package “vegan” (Oksanen et al. 2019, R Core Team 2020).

Checklist of the fish fauna of the Munim River Basin

Class Actinopteri

Notes: 

The checklist is presented in Table 2.

Table 2.

List of fish species recorded for the Munim River Basin in the present study. *endemic species to the hydrological units Maranhão and Parnaíba sensu Hubert and Renno (2006).

CLASS/ORDER/FAMILY/SPECIES

New records

Migratory species

Non-native species

Habitat of occurrence

Common name (Portuguese)

CLASS ACTINOPTERI

ACANTHURIFORMES

Ephippidae

Chaetodipterus faber (Broussonet, 1782)

X

Marine, Estuary and Freshwater

Peixe enxada

Gerreidae

Eugerres plumieri (Cuvier, 1830)

X

Marine, Estuary and Freshwater

Mojarra

Haemulidae

Conodon nobilis (Linnaeus, 1758)

X

Marine, Estuary and Freshwater

Genyatremus luteus (Bloch, 1790)

X

Marine and Estuary

Lutjanidae

Lutjanus jocu (Bloch & Schneider, 1801)

X

Marine, Estuary and Freshwater

Sciaenidae

Cynoscion steindachneri (Jordan, 1889)

X

Marine, Estuary and Freshwater

Macrodon ancylodon (Bloch & Schneider, 1801)

X

Marine and Estuary

Menticirrhus americanus (Linnaeus, 1758)

X

Marine and Estuary

Micropogonias furnieri (Desmarest, 1823)

X

Marine, Estuary and Freshwater

Curvina

Plagioscion squamosissimus (Heckel, 1840)

X

X

Freshwater

Curvina

Stellifer naso (Jordan, 1889)

X

Estuary and Freshwater

BATRACHOIDIFORMES

Batrachoididae

Batrachoides surinamensis (Bloch & Schneider, 1801)

X

Marine and Estuary

Pacamão

BELONIFORMES

Hemiramphidae

Hyporhamphus roberti (Valenciennes, 1847)

X

Marine and Estuary

Agulha

CARANGIFORMES

Achiridae

Achirus achirus (Linnaeus, 1758)

X

Marine, Estuary and Freshwater

Linguado

Carangidae

Chloroscombrus chrysurus (Linnaeus, 1766)

X

Marine and Estuary

Palombeta

Oligoplites palometa (Cuvier, 1832)

X

Marine, Estuary and Freshwater

Tibiro

Centropomidae

Centropomus parallelus Poey, 1860

X

Marine, Estuary and Freshwater

Robalo

CHARACIFORMES

Acestrorhynchidae

Acestrorhynchus falcatus (Bloch 1794)

Freshwater

Lubarana

Anostomidae

Leporinus aff. friderici

X

Freshwater

Piau de coco

Schizodon dissimilis (Garman 1890)

X

Freshwater

Piau de vara

Characidae

Aphyocharax sp.

Freshwater

Enfermerinha

Astyanax cf. bimaculatus

Freshwater

Piaba rabo de fogo

Brachychalcinus parnaibae Reis 1989

X

Freshwater

Piaba chatinha

Charax awa Guimarães, Brito, Ferreira & Ottoni, 2018*

Freshwater

Cacunda

Ctenobrycon cf. spilurus

Freshwater

Piaba

Hemigrammus sp. 1 sensu Oliveira et al. (2020)

Freshwater

Piaba

Hemigrammus sp.2 sensu Oliveira et al. (2020)

Freshwater

Piaba

Hemigrammus cf. rodwayi

Freshwater

Piaba

Hyphessobrycon piorskii Guimarães, Brito, Feitosa, Carvalho-Costa & Ottoni, 2018*

Freshwater

Tetra

Knodus guajajara Aguiar, Brito, Ottoni & Guimarães, 2022*

Freshwater

Piaba

Microschemobrycon sp.

Freshwater

Piaba

Moenkhausia sp.

Freshwater

Piaba

Moenkhausia cf. intermedia

Freshwater

Piaba

Moenkhausia oligolepis (Günther, 1864)

Freshwater

Piaba rabo preto

Phenacogaster cf. pectinata

Freshwater

Lambarizinho

Poptella compressa (Günther, 1864)

Freshwater

Piaba chatinha

Psellogrammus kennedyi (Eigenmann, 1903)

X

Freshwater

Roeboides margareteae Lucena, 2003*

Freshwater

Cacunda

Roeboides sazimai Lucena, 2007*

Freshwater

Cacunda

Serrapinnus sp.

Freshwater

Piabinha

Tetragonopterus argenteus Cuvier 1816

X

Freshwater

Piaba

Crenuchidae

Characidium sp.

Freshwater

Canivete, mocinha

Curimatidae

Curimatopsis aff. cryptica

Freshwater

Psectrogaster rhomboides Eigenmann & Eigenmann 1889

Freshwater

Branquinha

Steindachnerina notonota (Miranda Ribeiro, 1937)

Freshwater

João duro

Cynodontidae

Cynodon gibbus (Agassiz, 1829)

Freshwater

Gata

Erythrinidae

Hoplias malabaricus (Bloch, 1794)

Freshwater

Traíra

Hoplerythrinus unitaeniatus (Spix & Agassiz, 1829)

Freshwater

Gasteropelecidae

Gasteropelecus sternicla (Linnaeus, 1758)

Freshwater

Borboleta

Hemiodontidae

Hemiodus parnaguae Eigenmann & Henn, 1916*

Freshwater

Flecheiro

Iguanodectidae

Bryconops aff. affinis

Freshwater

Dórico

Lebiasinidae

Copella arnoldi (Regan, 1912)

Freshwater

Nannostomus beckfordi Günther, 1872

Freshwater

Peixe lápis

Triportheidae

Triportheus signatus (Garman, 1890)

X

Freshwater

Sardinha de água doce

Prochilodontidae

Prochilodus lacustris Steindachner, 1907*

X

Freshwater

Curimatá

Serrasalmidae

Colossoma macropomum (Cuvier, 1816)

X

X

X

Freshwater

Tambaqui

Metynnis lippincottianus (Cope, 1870)

Freshwater

Pacú

Myloplus rubripinnis (Müller & Troschel, 1844)

X

Freshwater

Pacú folha

Serrasalmus rhombeus (Linnaeus, 1766)

X

X

Freshwater

Pirambeba

Pygocentrus nattereri Kner, 1858

X

Freshwater

Piranha vermelha

CICHLIFORMES

Cichlidae

Aequidens tetramerus (Heckel, 1840)

Freshwater

Cará, Acará

Apistogramma piauiensis Kullander, 1980*

Freshwater

Carazinho

Cichlasoma zarskei Ottoni, 2011*

Freshwater

Cará preto, Acará, Cará

Crenicichla brasiliensis (Bloch, 1792)

Freshwater

Lope, Joana, Sabão

Geophagus parnaibae Staeck & Schindler, 2006*

Freshwater

Cará

Oreochromis niloticus (Linnaeus, 1758)

X

X

Estuary and Freshwater

Tilápia do nilo

Satanoperca jurupari (Heckel, 1840)

Freshwater

Cará bicudo

CLUPEIFORMES

Engraulidae

Anchovia surinamensis (Bleeker, 1865)

X

Estuary and Freshwater

Manjuba

Anchoviella guianensis (Eigenmann, 1912)

X

Estuary and Freshwater

Manjuba

Anchoviella lepidentostole (Fowler, 1911)

X

Marine, Estuary and Freshwater

Manjuba

Clupeidae

Opisthonema oglinum (Lesueur, 1818)

X

Marine and Estuary

Sardinha

Rhinosardinia amazonica (Steindachner, 1879)

X

Estuary and Freshwater

Sardinha

CYPRINODONTIFORMES

Anablepidae

Anableps anableps (Linnaeus, 1758)

X

Estuary and Freshwater

Tralhoto

Poeciliidae

Poecilia sarrafae Bragança & Costa, 2011

Freshwater

Barrigudinho

Rivulidae

Anablepsoides vieirai Nelson, 2016*

Freshwater

Peixe de poça

GYMNOTIFORMES

Apteronotidae

Apteronotus albifrons (Linnaeus, 1766)

Freshwater

Sarapó, Catana

Gymnotidae

Gymnotus carapo Linnaeus, 1758

Freshwater

Sarapó, Catana

Hypopomidae

Brachyhypopomus sp.

Freshwater

Sarapó, Catana

Sternopygidae

Eigenmannia robsoni Dutra, Ramos & Menezes 2022*

Freshwater

Sarapó, Catana

Sternopygus macrurus (Bloch & Schneider, 1801)

Freshwater

Sarapó, Catana

Rhamphichthyidae

Rhamphichthys atlanticus Triques, 1999*

Freshwater

Tubiba, Sarapó

MUGILIFORMES

Mugilidae

Mugil curema Valenciennes, 1836

Marine, Estuary and Freshwater

Sardinha

SILURIFORMES

Ariidae

Amphiarius rugispinis (Valenciennes, 1840)

X

Marine and Estuary

Bagre

Aspistor quadriscutis (Valenciennes, 1840)

X

Marine, Estuary and Freshwater

Bagre

Bagre bagre (Linnaeus, 1766)

X

Marine and Estuary

Bagre

Cathorops spixii (Agassiz, 1829)

X

Marine, Estuary and Freshwater

Bagre

Aspredinidae

Aspredo aspredo (Linnaeus, 1758)

X

Marine, Estuary and Freshwater

Banjo catfish

Pseudobunocephalus timbira Leão, Carvalho, Reis & Wosiacki, 2019

X

Freshwater

Auchenipteridae

Auchenipterus menezesi Ferraris & Vari, 1999*

X

Freshwater

Bagre

Tatia intermedia (Steindachner, 1877)

X

Freshwater

Bagrinho

Trachelyopterus galeatus (Linnaeus, 1766)

Freshwater

Cangati, Bagrinho

Callichthyidae

Aspidoras cf. raimundi

Freshwater

Cari

Callichthys callichthys (Linnaeus, 1758)

Freshwater

Cascudo

Corydoras julii Steindachner, 1906

X

Freshwater

Cari

Corydoras vittatus Nijssen, 1971*

X

Freshwater

Cari

Hoplosternum littorale (Hancock, 1828)

X

Freshwater

Cascudo

Megalechis thoracata (Valenciennes, 1840)

Freshwater

Cascudo

Doradidae

Hassar affinis (Steindachner, 1881)*

Freshwater

Cabeça de cavalo

Platydoras brachylecis Piorski, Garavello, Arce H. & Sabaj Pérez, 2008

X

Freshwater

Guirri

Loricariidae

Ancistrus cf. damasceni

Freshwater

Mão na cara, Cascudo, Bodó

Ancistrus sp.

Freshwater

Mão na cara, Cascudo, Bodó

Hemiodontichthys acipenserinus (Kner, 1853)

Freshwater

Cachimbo

Hypostomus cf. krikati

Freshwater

Boi de carro, Cascudo, Bodó

Hypostomus sp.

Freshwater

Boi de carro, Cascudo, Bodó

Hypoptopoma incognitum Aquino & Schaefer, 2010

X

Freshwater

Cascudo

Loricaria cf. cataphracta

Estuary and Freshwater

Cachimbo, Cascudo

Loricariichthys derbyi Fowler, 1915

X

Freshwater

Cachimbo, Cascudo

Rineloricaria sp.

Freshwater

Cachimbo, Cascudo

Heptapteridae

Imparfinis sp.

Freshwater

Mandi

Pimelodella parnahybae Fowler, 1941*

Freshwater

Mandi

Pimelodella sp1.

Freshwater

Mandi

Pimelodella sp2.

Freshwater

Mandi

Rhamdia quelen (Quoy & Gaimard, 1824)

X

Freshwater

Jundiá

Pimelodidae

Hemisorubim platyrhynchos (Valenciennes, 1840)

X

Freshwater

Mandi três pinta

Pimelodus blochii Valenciennes, 1840

X

X

Estuary and Freshwater

Mandi

Pimelodus ornatus Kner, 1858

X

Freshwater

Mandi dourado

Pseudoplatystoma fasciatum (Linnaeus, 1766)

X

X

Freshwater

Surubim

Sorubim lima (Bloch & Schneider, 1801)

X

Freshwater

Bico de pato

Pseudopimelodidae

Batrochoglanis sp.

Freshwater

Trichomycteridae

Ituglanis cf. amazonicus

Freshwater

SCOMBRIFORMES

Stromateidae

Peprilus paru (Linnaeus, 1758)

X

Marine and Estuary

SYNBRANCHIFORMES

Synbranchidae

Synbranchus marmoratus Bloch 1795

Freshwater and Estuary

Muçum

TETRAODONTIFORMES

Tetraodontidae

Lagocephalus cf. lagocephalus

X

Marine and Estuary

Baiacu arara

Analysis

The present study recorded about 32500 specimens belonging to 123 fish species (94 identified at the species level) for the Munim River Basin, divided into 49 families and 14 orders (Table 2, Suppl. materials 1, 2). The most diverse orders are the Characiformes, with 43 species (35%); Siluriformes, with 38 species (30.9%); Acanthuriformes, with 11 (8.9%); Cichliformes, with seven species (5.7%) and Gymnotiformes, with six species (4.9%), representing 85.4% of all species known from the river basin. The remaining orders (Clupeiformes, Carangiformes, Cyprinodontiformes, Batrachoidiformes, Beloniformes, Mugiliformes, Scombriformes, Synbranchiformes and Tetraodontiformes) together represent only 14.6% of the Munim River Basin species.

The most diverse family was the Characidae, with 21 species (17.1%), followed by the Loricariidae, with nine (7.3%) and the Cichlidae, with seven (5.7%). Further, from all 123 recorded species, only two, Oreochromis niloticus and Colossoma macropomum are non-native species for the studied region and 13 are migratory species (see Table 2). Amongst the species identified at the species level, 16 are endemic to the hydrographic regions of Maranhão and Parnaíba sensu Hubert and Renno (2006) (Mrn and Prn, respectively).

According to the General plotted curves (General species accumulation curve), the sampling effort can be considered sufficient (Fig. 6), given that the observed values of Sobs (125 ±14) are aligned with those calculated in the estimator Chao1 (136.25) and the asymptote estimates of the Michaelis-Menten equation (113), as well as the Bootstrap (140.8) and Jackknife1 (162.85) variation indicators (Fig. 6).

Figure 6.  

General species accumulation curve over the sampling period for this study.

Species Richness

There were significant differences in species richness between sections (X2= 16.207, df = 3, p < 0.001) where the Lower and Upper river basin sections had significantly more species than the Middle river basin section (p < 0.05, p < 0.01 respectively; Fig. 7).

Figure 7.  

Species richness values for all sample sites across river basin sections.

Fish assemblage composition

There was weak nestedness across the four basin sections (NODF = 37.67) and indices of species composition similarity and dissimilarity were moderate. Where Sørensen dissimilarity was 0.70 and Simpsons Index (i.e. true turnover) was 56%, suggesting that fish assemblage is distinct between basin sections but only moderately. Jaccard similarity was 83% indicating many shared species compared to unique species across river basin sections. Cluster analysis showed that the Estuary and Upper river sections were more distinct from the Lower and Middle river sections, which formed their own cluster (Fig. 8).

Figure 8.  

Hierachial cluster diagram of fish assemblage based on Jaccard Index per basin section using species presence-absence data.

Discussion

This long-term icthyological survey, covering 12 years, conducted between 2010 and 2022 (65% of the surveys were carried out between 2019 and 2022), applied different sampling gears over different water bodies and environments along the Munim River Basin and recorded a predominance of fishes belonging to the Characiformes and Siluriformes, agreeing with a pattern expected for the Neotropics (Lowe-Mcconnell 1999, Pelicice et al. 2005, Langeani et al. 2007, Polaz et al. 2014, Reis et al. 2016, Brito et al. 2019, Dagosta and de Pinna 2019, Guimarães et al. 2020, Castro and Polaz 2020). The study also recorded the predominance of small-sized characid fishes, which have a great diversity in the Neotropical Region, due to several traits, such as their high trophic plasticity (Abelha et al. 2001, Van Der Sleen and Albert 2018, Dagosta and de Pinna 2019, Castro and Polaz 2020, Guimarães et al. 2020, Corrêa and Castro 2021).

A total of 123 species were recorded, with only two of them representing introduced species to the studied river basin (Table 2 and Suppl. materials 1, 2). Colossoma macropomum (tambaqui) occurs naturally in the Amazon and Orinoco River Basins, thus being native to Brazil, but not the Munim River Basin (Latini et al. 2016, Fricke et al. 2022b); and Oreochromis niloticus (tilápia) which is native to northern and eastern Africa (Figueredo and Giani 2005, Latini et al. 2016, Fricke et al. 2022b). All the other 121 species are native to the studied area. Therefore, the fish assemblage composition of the Munim River Basin is currently little affected by the presence of alien fish species. However, the policy regarding non-native species and push for economic development indicates this may soon change (Azevedo-Santos et al. 2011, Doria et al. 2021, Faria et al. 2022).

The occurrence of non-native fish species usually comes from fish farming and, in some cases, from intentional release and aquarium trade (Latini et al. 2016, Rocha et al. 2023). Oreochromis nilotus is an omnivorous fish which has broad abiotic tolerances, rapid growth and high survival in environments with high population density, traits which facilitate invasiveness and are favoured in aquaculture species (Figueredo and Giani 2005, Latini et al. 2016). In Brazil, the cultivation of this species is increasing, frequently without any control (Figueredo and Giani 2005, Latini et al. 2016). The species C. macropomum was recorded at only one collection site (a single specimen) (see Suppl. materials 1, 2). This makes us believe that the specimen had probably accidentally escaped from local or home fish-farming. On the other hand, O. niloticus was recorded in four locations (some of these locations far from each other), on different dates (i.e. several specimens). These data suggest establishment in the river basin and, thus, should be considered an established species in the Munim River Basin. Aquaculture initiatives with poor biosecurity are the probable pathway of invasion and rapid expansion facilitated by favourable climatic conditions should be expected and monitored in the Munim River Basin (Charvet et al. 2021, Wilgen et al. 2022). There is likelihood of negative ecological impacts as a result of this burgeoning invasion, in particular O. niloticus is a highly efficient filter feeder and may disrupt the food-web (Vasconcelos et al. 2018, Charvet et al. 2021). Biological invasions are a direct cause of biodiversity decline globally and are an increasing threat, especially in aquatic systems with high endemicity (Havel et al. 2015, Gallardo et al. 2016).

This study reported 13 migratory fish species occurring in the Munim River Basin. Therefore, the eventual construction of dams and hydroelectric plants will undoubtedly negatively impact these species as migration routes will be interrupted. Locally, Oliveira et al. (2020) have already reported this situation occurring in the Mata de Itamacaoca, Chapadinha Municipality, State of Maranhão. They verified that the reservoir dam constructed in the Mata de Itamacaoca inhibits the dispersion of fish occurring below the dam, which possesses higher species diversity. In addition, migratory species were also not found by Oliveira et al. (2020) above the dam, in the reservoir, which would be a suitable habitat for these species. This may illustrate the effects of increased dam construction along the Munim River Basin.

When comparing the present checklist with previous ones listing the fish species found in the hydrographic regions of Maranhão and Parnaíba sensu Hubert and Renno (2006) (Mrn and Prn, respectively) (e.g. Soares (2005), Barros et al. (2011), Nascimento et al. (2016), Piorski et al. (2017), Brito et al. (2019), Brito et al. (2020), Guimarães et al. (2020)), it is evident that the fish diversity from the Munim River Basin has been underestimated. In fact, the present study showed a surprisingly high fish species diversity occurring in the Munim River Basin, when compared to the species richness found in other larger drainage systems and river basins from Maranhão. For example, Munim River Basin outnumbered the Itapecuru River Basin, a larger river basin, with 29 more species being recorded, where 94 fish species are known to occur (e.g. Barros et al. (2011), Nascimento et al. (2016), Koerber et al. (2022)). In addition, we recorded 67 more species than in the Preguiças and Periá River Basin, where 56 fish species are known to occur (e.g. Piorski et al. (2017), Brito et al. (2019), Brito et al. (2020), Koerber et al. (2022)); 22 more fish species than Guimarães et al. (2020) recorded for the Pindaré River drainage (101 fish species); and more than twice the number of fish species for the coastal river basins of Gurupi, Maracaçumé, and Turiaçu, where less than 50 species are known for each of these river basins (Koerber et al. 2022). There are only three studies surveying Maranhão coastal drainage systems, which presented a higher number of species than this study. Ramos et al. (2014), who recorded 146 species for the Parnaíba River Basin and, later, Silva et al. (2015) provided an updated list with six additional species (152). Koerber et al. (2022) published a checklist of the freshwater species in Maranhão (CLOFFBR-MA), listing 136 species for the Mearim River Basin. The Munim River Basin had 13 fewer species than those recorded in the Mearim River Basin, one of the largest river basins in Maranhão and 29 fewer species than the Parnaíba River Basin, which is the largest hydrographic basin in north-eastern Brazil (Ramos et al. 2014, Silva et al. 2015, Koerber et al. 2022).

When analysing the present results in light of the previous surveys in the Munim River Basin, it is clear that all previous studies were geographically restricted to specific localities, extremely close to each other, thus were not able to depict and represent the wider basin diversity. Ribeiro et al. (2014) recorded only 20 fish species (103 less than the present study), using a traditional fishing technique called "moita" commonly used by local traditional communities in the Chapadinha Municipality. However, this method is biased toward the capture of medium to large-sized fishes and is generally applied by subsistence fisheries. Matavelli et al. (2015) surveyed the tadpoles occurring in lentic and lotic environments in Cerrado and Restinga vegetation types, sampling in localities in the Munim and Parnaíba river basins. Fish species were also sampled and a total of 13 species were recorded from the Munim River Basin (110 less than the present study). Nunes et al. (2019) carried out a weight-length ratio study of the fish community in one locality in Munim River Basin, recording 15 fish species (108 less than the present study). More recently, Oliveira et al. (2020) published a freshwater fish species list of a conservation unit in the Chapadinha Municipality after a long monitoring period, with 23 species (100 less than the present study). However, the survey was focused on small streams and consequently recorded mainly small-size species. Guimarães et al. (2021b) published a book from the same area studied by Oliveira et al. (2020), directed at the general public, which focused on species with an estimated high ornamental value. Finally, in the CLOFFBR-MA, which relied upon literature information, 59 species were identified in the Munim River Basin (64 less than the present study) (Koerber et al. 2022). None of these previous studies had the main goal of identifying the entire species diversity of the Munim River Basin.

Within the 121 native species listed in the present study, 29 were not able to be identified to the species level. Guimarães et al. (2018a) and Guimarães et al. (2020), hypothesised that probably this is a result of the lack of taxonomic knowledge and information about these species and groups occurring in Maranhão. The taxa which could not be identified to the species level, likely belong to species complexes or represent taxonomically challenging and poorly defined groups and may represent new species to science (see Table 2).

Median species richness in the Middle river basin section was lower than in the Upper and Lower river basin sections; however, the Middle section had both more sampling sites and much higher range of species richness. Environmental filtering across river gradients has a strong influence on species richness and diversity (López‐Delgado et al. 2019, Walsh et al. 2022). By grouping by section, we are missing local habitat-specific variables which are likely to be driving differences in fish assemblages across a highly heterogenous river network. Investigating habitat specific associations and drivers of beta diversity will vastly improve our understanding of drivers of fish assemblages in the Munim River Basin. Moderate nestedness and similarity/dissimilarity trends, combined with the lack of clear clustering between sites within river basin sections, indicate that fish assemblage structuring in the Munim River Basin is probably driven by both the river continuum concept as well as environmental filtering (Vannote et al. 1980, Heino et al. 2015). However, unobstructed flows facilitating dispersal likely drive high similarity throughout each basin section (Leitão et al. 2018). The Munim River Basin is not high altitude and has neither large rapids nor large waterfalls; therefore, the flow conditions through the sections are also relatively similar, with the lower river section differing through estuarine influence. Further research is needed to understand the specific microhabitats and fish associations throughout the river basin as this is undoubtedly a driving factor of diversity. For example, river slope and flow conditions exert strong environmental filters on fish community and traits in Neotropical and Afrotropical freshwaters and dispersal between heterogenous habitats may be limited by side channels and swamp habitats (Caetano et al. 2021, Walsh et al. 2022). A higher concentration of specialist species is expected to be found in the Upper section as there is more competition for niches (Sternberg and Kennard 2013). The cluster analysis indicated that the Upper section sites were on distinct branches from the other sites, but a standardised sampling methodology combined with implementation of functional trait-based approaches will facilitate our understanding of finer scale processes of environmental filtering in each section (Bower and Winemiller 2019a, Bower and Winemiller 2019b).

Considering all 92 native species which were identified to the species level, 30 of them (Achirus achirus, Amphiarius rugispinis, Anableps anableps, Anchovia surinamensis, Anchoviella guianensis, Anchoviella lepidentostole, Aspistor quadriscutis, Aspredo aspredo, Bagre bagre, Batrachoides surinamensis, Cathorops spixii, Centropomus parallelus, Chaetodipterus faber, Chloroscombrus chrysurus, Conodon nobilis, Cynoscion steindachneri, Eugerres plumieri, Genyatremus luteus, Hyporhamphus roberti, Lutjanus jocu, Macrodon ancylodon, Menticirrhus americanus, Micropogonias furnieri, Mugil curema, Oligoplites palometa, Opisthonema oglinum, Peprilus paru, Plagioscion squamosissimus, Rhinosardinia amazonica and Stellifer naso) are commonly found in brackish water or estuaries. Due to this, no biogeographical considerations will be made about them. From the remaining 62 species identified to the species level, 16 are only known from river drainage systems and basins of the Maranhão State and the Parnaíba River Basin (Anablepsoides vieirai, Apistogramma piauiensis, Auchenipterus menezesi, Charax awa, Cichlasoma zarskei, Corydoras vittatus, Eigenmannia robsoni, Geophagus parnaibae, Hassar affinis, Hemiodus parnaguae, Hyphessobrycon piorskii, Pimelodella parnahybae, Prochilodus lacustris, Rhamphichthys atlanticus, Roeboides margareteae and Roeboides sazimai). Three other species (Platydoras brachylecis, Poecilia sarrafae and Schizodon dissimilis) are also known from other drainages in the northeast of Brazil (Teixeira et al. 2017, Silva et al. 2020, Fricke et al. 2022b). The remaining 43 species are also known from different Amazonian drainage systems (Fricke et al. 2022b), a pattern clearly showing the influence and presence of Amazonian fauna in the Munim River Basin. In addition, when comparing the species listed for the Munim River Basin to the list of species in the Parnaíba River (Ramos et al. 2014, Silva et al. 2015), there are 53 native species co-occurring in both drainage systems, showing a high influence of the larger Parnaíba River Basin over smaller coastal drainage systems. Finally, there are a total of 64 new records of fish species for the Munim River Basin and 48 new records considering only the number of taxa identified at the species level (Table 2), showing that, until the present study, the drainage's diversity was underestimated.

The Munim River Basin, previously a neglected river system, similar to many other coastal systems in Maranhão, is now one of the better known river basins relative to its fish diversity. A detailed taxonomic investigation of specimens sampled over a 12 year period revealed a much diverse fish fauna. The present study is the most comprehensive carried out in the Munim River Basin so far, adding 64 species (including species identified at the species level and species not identified at species level), which were previously considered not to occur in the drainage, resulting in a total of 123 species. Within this species richness, there was a large number of taxa, which could not be identified at the species level, indicating the urgent need for dedicated taxonomic research in the region. This study puts emphasis on the importance of compiling ichthyofaunal lists for poorly-studied or subsampled areas. This achievement represents a first step in understanding the diversity in the Munim River Basin, with the information presented herein allowing the development of future ecology, biogeography and conservation studies. Thus, this is an essential contribution to the effort to better understand the fish diversity of Maranhão in the face of rapid global change and habitat alteration. Despite the high number of species found for the Munim River Basin, more collection efforts are recommended, especially in the Lower and Estuary sections. New collection expeditions may find species that may not have been recorded by this work.

Acknowledgements

We thank Ananda Saraiva for helping to identify some specimens of Loricariinae; Elioenai Oliveira, Antônio Bezerra and Brenda Lima for laboratory assistance; four anonymous reviewers for their important contributions to the manuscript; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES - Finance Code 001), Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA), Conselho Nacional de Desenvolvimento (CNPQ), Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) and Fundação Amazônia de Amparo a Estudos e Pesquisas (FAPESPA) for providing the scholarship under the process (CNPq-FAPEMA, grant PDCTR-08797/22 to PSB), (FAPESPA; grant 028/2021 to ECG), (CNPq; grant 307974/2021-9 to FPO), (CNPq-IC; grant 134775/2020-1 to RFO), (FAPEMA; grant BM-00809/22 to LOV), (FAPEMA-IC; grants BIC-01958/20 and BIC-04123/21 to MSPC), (FAPERJ; grant E–26/202.005/2020 to AMK) and (CAPES; grant 88887.674455/2022-00 to DSC). This study was supported by the projects “PROCESSO UNIVERSAL-00724/17” and “Processo UNIVERSAL-00437/19”, from FAPEMA.

Author contributions

Conceptualisation: Felipe Ottoni, Erick Guimarães, Lucas Vieira. Data collecting, organising and curation: Lucas Vieira, Rafael Oliveira, Diego Campos, Marcony Coelho, Maurício Paiva, Erick Guimarães, Pâmella Brito, Felipe Ottoni. Specimens identification: Lucas Vieira, Rafael Oliveira, Diego Campos, Marcony Coelho, Maurício Paiva, Erick Guimarães, Pâmella Brito, Axel Katz, Felipe Ottoni. Supplementary material: Lucas Vieira. Ecological and statistics analyses: Josie South, Diego Campos. Manuscript writing: Lucas Vieira, Felipe Ottoni, Josie South, Pedro Bragança, Diego Campos, Marcony Coelho, Maurício Paiva, Rafael Oliveira, Erick Guimarães, Pâmella Brito, Jadson Santos, Axel Katz. Map and river basin sectorisation: Diego Campos. Photographs: Lucas Vieira and Rafael Oliveira. Photographs editing: Axel Katz. Supervision: Felipe Ottoni, Pedro Bragança, Josie South. English language review: Pedro Bragança, Josie South. All authors have read and agreed to the published version of the manuscript.

References

Supplementary materials

Suppl. material 1: Checklist of the fish fauna of the Munim River Basin, Maranhão, north-eastern Brazil 
Authors:  Lucas Vieira
Data type:  Excel csv spreadsheet
Brief description: 

Spreadsheet in Darwin Core format.

Suppl. material 2: Checklist of the fish fauna of the Munim River Basin, Maranhão, north-eastern Brazil 
Authors:  Lucas Vieira
Data type:  Excel csv spreadsheet
Brief description: 

Spreadsheet used in ecological and statistics analyses.

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