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​

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Introduction​

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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 7–9^th 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

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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​

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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.

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.

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).