Description of three new species of Eigenmannia (Gymnotiformes: Sternopygidae) from the rio Mearim and rio Parnaíba basins, Northeastern Brazil

Guilherme Moreira Dutra1 , Telton Pedro Anselmo Ramos2 and Naércio Aquino Menezes1

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Abstract​


EN

Three new species of Eigenmannia belonging to the E. trilineata species-group are described. The first species is described from rio Mearim basin and can be diagnosed by lateral line stripe restricted to last two thirds of body, superior midlateral stripe present, 176–205 anal-fin rays, 10–15 scales rows above lateral line, 109–125 lateral line scales, 19–23 premaxillary teeth, 20–29 dentary teeth, 6–10 endopterygoid teeth, and 13–14 precaudal vertebrae. The second species is described from upper rio Parnaíba, and can be diagnosed by lateral line stripe restricted to last two-thirds of body, ii,11–13 pectoral-fin rays, 180–196 anal-fin rays, 12–15 scales rows above lateral line, 10–14 premaxillary teeth, 15–21 dentary teeth, 8–10 endopterygoid teeth, and 14 precaudal vertebrae. The third species is widespread in rio Parnaíba basin, and can be diagnosed by absence of lateral line stripe, absence of superior midlateral stripe, 182–228 anal-fin rays, 12–15 scales rows above lateral line, 107–131 lateral line scales, 32–34 premaxillary teeth, 35–44 dentary teeth, 9–12 endopterygoid teeth, and 13 precaudal vertebrae. A dichotomous key and the conservation status for the three species are provided.

Keywords: Electric fishes, Eigenmannia trilineata species-group, Identification key, Taxonomy.

PT

Três espécies novas de Eigenmannia pertencentes ao grupo E. trilineata são descritas. A primeira espécie é descrita para a bacia do rio Mearim e pode ser diagnosticada por apresentar faixa da linha lateral restrita aos últimos dois terços do corpo, faixa médio lateral superior presente, 176–205 raios na nadadeira anal, 10–15 fileiras de escamas acima da linha lateral, 109–125 escamas na linha lateral, 19–23 dentes pré-maxilares, 20–29 dentes no dentário, 6–10 dentes no endopterigóide, e 13–14 vértebras pré-caudais. A segunda espécie é descrita do alto rio Parnaíba, e pode ser diagnosticada por apresentar faixa da linha lateral restrita aos últimos dois terços do corpo, ii,11–13 raios na nadadeira peitoral, 180–196 raios na nadadeira anal, 12–15 fileiras de escamas acima da linha lateral, 10–14 dentes pré-maxilares, 15–21 dentes no dentário, 8–10 dentes no endopterigóide, e 14 vértebras pré-caudais. A terceira espécie está amplamente distribuída na bacia do rio Parnaíba, e pode ser diagnosticada pela ausência de faixa na linha lateral, ausência da faixa médio lateral superior, 182–228 raios na nadadeira anal, 12–15 fileiras de escamas acima da linha lateral, 107–131 escamas na linha lateral, 32–34 dentes pré-maxilares, 35–44 dentes no dentário, 9–12 dentes no endopterigóides, e 13 vértebras pré-caudais. Uma chave dicotômica e o status de conservação para as três espécies são fornecidas.

Palavras-chave: Chave de identificação, Peixes elétricos, grupo de espécies Eigenmannia trilineata, Taxonomia.

Introduction​


Eigenmannia Jordan & Evermann is the most species-rich genus of the Sternopygidae, comprising 27 valid species (Ferraris et al, 2017; Campos-da-Paz, Queiroz, 2017; Dutra et al., 2017, 2018, 2021; Peixoto, Waltz, 2017; Waltz, Albert, 2018; Peixoto, Ohara, 2019; Herrera-Collazos et al., 2020; Peixoto et al., 2021). It includes small to medium-sized fishes (120–490 mm TL) that are widely distributed throughout the Neotropics, from the Río Tuíra basin in Panamá to the Río de La Plata basin in Argentina (Waltz, Albert, 2017). The monophyly of Eigenmannia was recently demonstrated by Alda et al. (2019) based on the analysis of ultra-conserved genetic elements and ratified by Dutra et al. (2021) on the basis of four morphological synapomorphies: (1) presence of “epipleurals” at 7–9th vertebrae, (2) Nervus opticus thicker than Nervus olfactorius, (3) number of premaxillary teeth (30–37), and (4) five premaxillary teeth rows. 

In the Parnaíba ecoregion (sensu Abell et al., 2008), the first record of Eigenmannia was made by Fowler (1941), who suggested the presence of E. virescens (Valenciennes, 1836) in the rio Parnaíba at Teresina. Subsequently, E. virescens was reported in the same basin by Ramos et al. (2014), and in its tributaries rio Gurgueia (Silva et al., 2015), and rio Longá (Melo et al., 2016). Likewise, E. virescens has also been reported in the rio Itapecuru and rio Pindaré, tributaries of Mearim basin (Piorski, 1998; Guimarães et al., 2020), another relatively large drainage of northeastern Brazil. However, Peixoto et al. (2015) argue that the distribution of E. virescens is restricted to the lower portions of the rio Paraná basin and the Río la Plata. Consequently, there is a clear necessity to reevaluate the identity of Eigenmannia populations in the rio Mearim and rio Parnaíba basins. Thus, the aim of this study is to conduct a comprehensive taxonomic revision of Eigenmannia in these basins.

Material and methods


All measurements were taken point-to-point to the nearest 0.1 mm with digital calipers under a stereomicroscope, preferably on the left side. Measurements and counts followed Peixoto et al. (2015). Measurements reported as a percentage of total length and length to end of anal-fin base are given only for specimens without damage or regeneration. In the description, frequencies are given in parentheses after each count and an asterisk indicates counts for the holotype. Osteological data were obtained via specimens that were cleared and stained using the technique of Taylor, Van Dyke (1985). Precaudal vertebrae includes four vertebrae of the Weberian complex plus all remaining vertebrae without fully developed hemal spines. Transitional vertebrae are post-Weberian precaudal vertebrae lacking both pleural ribs and hemal spines (Hopkins, 1991). The nomenclature of stripes follows Peixoto et al. (2015) and Peixoto, Wosiacki (2016) (Fig. 1). Information from literature was also used for comparisons (Waltz, Albert, 2018; Herrera-Collazos et al., 2020). Abbreviations used in the text are: CS = cleared and counterstained, HL = head length, and LEA = length to the end of the anal fin. Institutional abbreviations follow Sabaj (2019).

FIGURE 1 | Schematic showing the body stripe nomenclature of Peixoto et al. (2015) and Peixoto, Wosiacki (2016).

Results​


Eigenmannia bumba, new species

urn:lsid:zoobank.org:act:3F3C0B90-6FB3-43E8-9B03-A158FD487271

(Figs. 2, 3A, B; Tab. 1)

Eigenmannia virescens (non Valenciennes, 1836). — Guimarães et al., 2020:7 (listed, ichthyofauna of the Pindaré River).

Holotype. MZUSP 125870, 117.5 mm LEA, rio Santana, tributary of rio Grajaú, rio Mearim basin, Grajaú, Maranhão, Brazil, 05°35’39.48”S 46°14’30.88”W, O. Oyakawa, F. Dagosta, M. Marinho & P. Camelier, 16 Out 2014.

Paratypes. MZUSP 123709, 22+3CS, 77.5–123.5 mm LEA; MZUSP 123714, 21, 53.6–107.1 mm LEA, collected with holotype.

Non-types. MZUSP 5065, 1, 89.7 mm LEA, Rio Grajaú, Grajaú, Maranhão, 5°49”S 46°09’W, Expedição do Departamento de Zoologia, 15 Jun 1966. MZUSP 125873, 1, 83.9 mm LEA, Rio Pindaré, Bom Jesus das Selvas, Maranhão, 4°36’32.6”S 46°56’09.2”W, O. Oyakawa, F. Dagosta, M. Marinho, P. Camelier, 21 Out 2014.

Diagnosis. Eigenmannia bumba, a member of the E. trilineata species-group, differs from the E. humboldtii species-group by the anal-fin hyaline (vs. anal-fin margin distinctly darkened), and from E. macrops (Boulenger, 1897) by the absence of enlarged eye (21.3–25.4% HL vs. 26.4–29.7% HL), and the presence of a short caudal filament (19.2–30.8% LEA vs. 67.5–79.3% LEA). Within the E. trilineata species-group,the new species differs from all other species, except E. besouro Peixoto & Wosiacki, 2016, E. correntes Campos-da-Paz & Queiroz, 2017, E. dutrai Peixoto, Pastana & Ballen, 2021, E. guchereauae (Meunier, Jegu & Keith, 2014), E. meeki Dutra, de Santana & Wosiacki, 2017, E. oradens Dutra, Peixoto, de Santana & Wosiacki, 2018, E. robsoni, E. sirius Peixoto & Ohara, 2019, E. vicentespeleaea Triques, 1996, E. virescens, and E. waiwai Peixoto, Dutra & Wosiacki, 2015 by having a subterminal mouth (vs. terminal). Eigenmannia bumba differs from the aforementioned species by the following combination of characters: (1) lateral line stripe restricted to last two thirds of body (vs. complete in E. besouro, E. correntes, E. dutrai, E. guchereauae, E. meeki, E. oradens, E. sirius, E. vicentespelaea, and E. waiwai); (2) superior midlateral stripe present (vs. absent in E. guchereauae E meeki, E. oradens, E. robsoni, and E. virescens); (3) 176–205 anal-fin rays (vs. 143–154 in E. correntes, 211–204 in E. meeki); (4) 10–15 scales rows above lateral line (vs. 7–8in E. vicentespelaea); (5) 109–125 scales on lateral line (vs. 140–168 in E. meeki), (6) 19–23 premaxillary teeth (vs. 75 in E. guchereauae, 30–55 in E. meeki, 38–42 in E. oradens, 32–34 in E. robsoni,25–26 in E. vicentespeleaea, and 35–40 in E. waiwai); (7) 20–29 dentary teeth (vs. 16–18 in E. correntes, 35–36 in E. dutrai, 88 in E. guchereauae, 31–38 in E. oradens, 35–44 in E. robsoni,38–41 in E. vicentespelaea, 39 in E. virescens, and 37–38 in E. waiwai); (8) 6–10 endopterygoid teeth (vs. 13–15 in E. meeki,14–17 in E. waiwai); (9) depth of posterodorsal expansion on infraorbitals 1+2 half as long as infraorbitals 1+2 length (vs. as long as infraorbitals 1+2 length in E. dutrai, E. guchereauae, E. oradens, E. sirius); (10) basibranchial 1 unossified (vs. ossified in E. virescens); (11) 13–14 precaudal vertebrae (vs. 15 in E. meeki and E. sirius); (12) length of coronomeckelian bone corresponding to 20% of Meckel’s cartilage length (vs. 45% in E. oradens and E. waiwai). A summary of diagnostic characters among species of the E. trilineata species-group is provided on Tabs. 2–3.

Description. Body shape and pigmentation shown in Fig. 2, morphometric data in Tab. 1. Largest examined specimen 123.5 mm LEA. Body elongate and distinctly compressed. Greatest body depth at vertical crossing distal tip of pectoral fin. Dorsal profile of body slightly convex from snout tip to vertical through anal-fin terminus. Ventral profile of body convex from tip of lower jaw to anal-fin terminus. Caudal filament short.

FIGURE 2 | Eigenmannia bumba, MZUSP 125870, holotype, 117.5 mm LEA, rio Santana, Grajaú, Maranhão, Brazil, 05°35’39.48”S 46°14’30.88”W. A. lateral view of head, B. lateral view of body.

TABLE 1 | Morphometrics for examined specimens of Eigenmannia bumba, E. cacuria, and E. robsoni.

 

Eigenmannia bumba

Eigenmannia cacuria

Eigenmannia robsoni

 

Holotype

Min

Max

Mean

SD

N

Holotype

Min

Max

Mean

SD

N

Holotype

Min

Max

Mean

SD

N

Total length (mm)

117.5

104.8

148.7

15

152.4

74.9

152.4

7

175.1

83.8

151.8

19

Length to end of anal fin (mm)

148.7

83.5

123.5

15

110.0

53.6

134.0

10

139.3

110.5

207.0

14

Head length (mm)

14.0

11.3

16.5

15

12.9

7.5

14.3

10

16.1

12.1

19.0

19

Caudal-filament length (mm)

31.2

17.0

31.2

15

42.5

21.3

42.5

7

35.8

21.9

55.2

14

Percent of length to the end of anal fin

Caudal-filament length

26.6

19.2

30.8

24.7

3.4

15

38.6

26.4

41.3

36.7

4.9

7

25.7

19.9

36.4

27.2

5.0

14

Greatest body depth

17.7

15.5

17.7

16.4

0.7

15

16.1

14.8

17.8

16.6

0.8

9

13.9

13.5

18.7

15.6

1.7

17

Body depth at anal-fin origin

15.3

13.2

15.5

14.4

0.8

15

14.7

12.9

16.2

14.9

0.9

9

12.8

12.8

18.5

14.5

1.6

18

Body width

7.2

5.4

7.6

6.4

0.6

15

6.2

5.3

7.6

6.5

0.6

9

5.6

4.9

8.5

6.0

0.9

18

Preanal-fin distance

17.1

15.4

18.9

17.6

0.9

15

16.3

13.3

19.1

17.1

1.7

9

14.7

14.7

20.2

17.1

1.8

18

Prepectoral-fin distance

13.2

10.1

15.8

13.8

1.6

15

12.5

11.2

15.0

13.7

1.2

9

12.8

10.2

16.5

13.9

1.5

18

Anal-fin length

85.4

78.1

89.4

84.8

2.8

15

86.4

82.5

88.3

86.0

1.5

9

87.5

81.3

89.9

85.0

2.6

18

Pectoral-fin length

8.4

8.4

10.6

9.8

0.6

15

8.2

7.2

10.3

8.6

1.1

9

8.8

0.0

12.2

9.5

2.6

18

Snout to anus

7.6

7.6

12.2

9.7

1.3

15

7.6

6.0

13.6

10.1

2.7

9

7.5

6.9

12.1

8.9

1.5

17

Head length

11.9

11.9

14.1

13.2

0.7

15

11.7

10.7

14.0

12.9

1.1

9

11.5

11.5

15.0

13.1

1.1

18

Percent of head length

Head width at opercle

59.2

52.6

59.3

57.0

1.9

15

59.5

54.8

64.7

58.8

3.1

10

55.7

51.0

61.4

55.1

3.0

19

Head width at eye

52.2

40.6

52.2

48.2

3.0

15

50.0

41.6

52.5

47.9

3.6

10

47.0

42.1

49.8

45.4

2.1

19

Head depth at nape

81.0

76.1

83.3

79.5

2.2

15

86.5

81.4

89.6

85.5

3.0

10

81.6

73.3

88.0

79.3

3.9

19

Head depth at eye

59.7

57.6

66.5

61.8

2.5

15

69.2

58.6

69.2

65.1

3.3

10

62.6

54.9

66.2

60.2

3.0

19

Snout length

32.4

31.7

37.0

33.7

1.3

15

35.3

29.1

35.3

32.2

1.7

10

37.2

30.5

37.2

33.7

1.9

19

Snout to posterior nostril

24.7

21.1

24.7

22.9

1.2

15

23.2

20.8

24.8

22.8

1.1

10

25.1

20.3

26.0

23.6

1.5

19

Posterior nostril to eye

10.6

8.3

11.6

9.9

0.9

15

11.3

8.5

12.7

10.7

1.2

10

10.4

8.4

23.9

10.7

3.5

19

Postorbital distance

48.1

48.0

53.3

50.0

1.7

15

54.8

49.8

54.9

52.6

1.8

10

55.2

48.2

57.8

52.1

2.7

19

Branchial opening

31.6

26.8

36.9

30.6

2.7

15

30.5

27.9

33.6

30.7

1.8

10

27.4

24.7

32.9

30.4

2.2

19

Internarial width

19.2

16.8

23.4

20.0

1.7

15

19.7

17.2

21.0

19.9

1.1

10

21.4

17.4

21.5

19.9

1.1

19

Internarial distance

12.5

10.5

13.5

11.9

0.9

15

12.0

10.5

13.3

11.9

0.9

10

11.1

9.3

14.1

11.7

1.1

19

Interorbital distance

34.9

31.0

36.6

33.1

1.5

15

41.6

34.3

43.1

39.0

2.5

10

33.4

29.1

36.4

32.1

1.9

19

Eye diameter

21.6

21.3

25.4

23.8

1.3

15

17.5

17.5

21.1

19.0

1.1

10

18.1

17.2

24.5

20.6

1.9

19

Mouth length

19.3

17.1

23.6

19.3

1.8

15

23.4

18.4

23.5

21.1

1.9

10

19.0

17.1

23.6

20.2

1.6

19

Mouth width

18.7

16.6

20.3

18.4

1.1

15

18.8

14.5

22.2

19.2

2.1

10

17.6

16.2

21.3

18.1

1.3

19

Percent of caudal filament length

Caudal-filament width

3.6

3.0

4.4

3.7

0.4

9

2.7

1.8

3.5

2.8

0.6

7

4.2

2.2

7.7

3.9

1.6

12

Caudal-filament depth

6.1

4.8

10.2

6.8

1.6

9

3.6

3.3

6.5

4.3

1.1

7

8.4

4.7

10.2

6.9

1.6

12

 

TABLE 2 | Summary of external and osteological diagnostic characters for the 26 recognized species of the Eigenmannia trilineata species-group. Table redrawn and modified from Waltz, Albert (2018) based on compiled data from Peixoto et al. (2015), Peixoto, Wosiacki (2016), Campos-da-Paz, Queiroz (2017), Dutra et al. (2017, 2018, 2021), Peixoto, Waltz (2017), Peixoto, Ohara (2019), Herrera-Collazos et al. (2020), and Peixoto et al. (2020). Dashes represent data not available in the literature.

 

 

Mouth

position

Lateral line

stripe

Superior

midlateral

stripe

Size of teeth along dentigerous surface of dentary

Depth of posterodorsal expansion on infraorbitals 1+2 (IO 1+2)

Coronomeckelian bone length

Basibranchial 1

E. antonioi

terminal

present

present

increasing in size

as long as IO 1+2 length

20% MC

unossified

E. besouro

subterminal

present

present

all similar in size

40% as long as IO 1+2 length

30% MC

unossified

E. bumba

subterminal

present

present

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. cacuria

terminal

present

present

increasing in size

as long as IO 1+2 length

20% MC

unossified

E. camposi

terminal

present

E. correntes

subterminal

present

present

increasing in size

40% as long as IO 1+2 length

20% MC

unossified

E. desantanai

terminal

present

present

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. dutrai

subterminal

present

present

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. guairaca

terminal

present

present

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. guchereauae

subterminal

present

absent

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. loretana

terminal

present

present

60–75% as long as IO 1+2 length

20% MC

E. magoi

terminal

present

present

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. matintapereira

terminal

present

present

all similar in size

half as long as IO 1+2 length

20% MC

unossified

E. meeki

subterminal

present

absent

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. microstoma

terminal

present

present

all similar in size

as long as IO 1+2 length

45% MC

unossified

E. muirapinima

terminal

present

present

increasing in size

as long as IO 1+2 length

20% MC

unossified

E. oradens

subterminal

present

absent

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. pavulagem

terminal

present

present

increasing in size

as long as IO 1+2 length

20% MC

unossified

E. robsoni

subterminal

absent

absent

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. sayona

terminal

present

present

increasing in size

as long as IO 1+2 length

20% MC

ossified

E. sirius

subterminal

present

present

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. trilineata

terminal

present

present

all similar in size

half as long as IO 1+2 length

20% MC

unossified

E. vicentespelaea

subterminal

present

present

all similar in size

as long as IO 1+2 length

20% MC

unossified

E. virescens

subterminal

absent

absent

all similar in size

half as long as IO 1+2 length

20% MC

ossified

E. waiwai

subterminal

present

present

all similar in size

half as long as IO 1+2 length

20% MC

unossified

E. zenuensis

terminal

present

present

 

TABLE 3 | Summary of meristic diagnostic characters for the 26 recognized species of the Eigenmannia trilineata species-group. Table redrawn and modified from Waltz, Albert (2018) based on compiled data from Peixoto et al. (2015), Peixoto, Wosiacki (2016), Campos-da-Paz, Queiroz (2017), Dutra et al. (2017, 2018, 2021), Peixoto, Waltz (2017), Peixoto, Ohara (2019), Herrera-Collazos et al. (2020), and Peixoto et al. (2021).

 

 

Pectoral-fin rays

Anal-fin rays

Scale rows above lateral line

Premaxillary teeth

Dentary teeth

Endopterygoid teeth

Precaudal vertebrae

E. antonioi

ii,13–14

166–207

8–10

8–12

8–15

8–9

13–14

E. besouro

ii,12–15

150–198

7–10

18–29

19–30

10–11

14

E. bumba

ii,13–15

176–205

10–15

19–23

20–29

6–10

13–14

E. cacuria

ii,11–13

180–196

12–15

10

15–21

8–10

14

E. camposi

ii,12–15

173–217

7–10

27

20–22

9–10

13

E. correntes

ii,12–13

143–154

11–12

11–20

16–18

4–9

14

E. desantanai

ii,12–14

170–198

8–10

24–25

21–23

14–15

11–12

E. dutrai

ii,14–16

171–206

9–11

23–29

35–36

9–18

14–16

E. guairaca

ii,11–12

151–170

14–15

9–10

17–19

5–6

15

E. guchereauae

ii,16–19

184–187

8–12

75

88

?

13–14

E. loretana

ii,13–14

162–196

9–13

11–15

17–19

6–7

13–14

E. magoi

ii,11–16

182–259

6–18

32

35–39

11

14

E. matintapereira

ii,16–17

216–222

10–12

22–24

25–27

9–12

13

E. meeki

ii,13–17

211–240

10–15

30–35

21–23

13–15

15

E. microstoma

ii,12–15

173–207

11–15

16

16

11–16

14–16

E. muirapinima

ii,11–12

170–198

8–13

8–10

11–16

8–9

13–14

E. oradens

ii,16–17

164–192

8–11

38–42

31–38

10

14

E. pavulagem

ii,13–14

176–201

8–12

13–16

15–21

8–11

13–15

E. robsoni

ii,12–15

182–228

12–15

25–30

35–40

9–12

13

E. sayona

ii,12–13

198–217

9–11

17

19–26

8–9

13

E. sirius

ii,13–15

157–183

9–12

15–24

15–33

9–13

15

E. trilineata

ii,14–15

176–217

9–12

31–33

23

16–17

14

E. vicentespelaea

ii,15–17

169–225

7–8

25–26

38–41

10–5

13–14

E. virescens

ii,16–17

173–225

9–11

22

39

9

14

E. waiwai

ii,12–16