Research Article |
Corresponding author: Marcelo C. Andrade ( andrademarcosta@gmail.com ) Academic editor: Carole Baldwin
© 2016 Marcelo C. Andrade, Michel Jégu, Tommaso Giarrizzo.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Andrade MC, Jégu M, Giarrizzo T (2016) A new large species of Myloplus (Characiformes, Serrasalmidae) from the Rio Madeira basin, Brazil. ZooKeys 571: 153-167. https://doi.org/10.3897/zookeys.571.5983
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Myloplus zorroi sp. n. is described from the Rio Madeira Basin in Amazonia. The new species had been treated as an undescribed Tometes species because of the absence of a marked abdominal keel and few small spines forming its prepelvic serrae, features commonly found in the species of the Myleus clade of the Serrasalmidae (species of genera Myleus, Mylesinus, Ossubtus and Tometes) and also in species of Utiaritichthys. Myloplus zorroi sp. n. shares the following characters with its congeners and Utiaritichthys: molariform teeth (versus incisiform teeth in Myleus clade members); a labial row of premaxillary teeth separated from lingual row by an internal gap (versus absence of internal gap between premaxillary teeth rows); and an ascending process of premaxilla wide from its base to the tip (versus ascending process tapering from its base to the tip). Like other Myloplus species, M. zorroi sp. n. differs from Utiariticthys by having a deeper body, approximately 60% of standard length (versus usually less than 50% of standard length). Considering all the morphological evidence, including the presence of 13–19 low spines forming the prepelvic serrae in M. zorroi sp. n. versus more than 20 high spines forming a marked prepelvic keel in other species of Mylopus, the new species is here assigned to Myloplus. Comparisons of the new species with nominal species of Myloplus, representatives of the Myleus clade, and other related taxa are provided.
Ostariophysi, Myleus, rapids, pacu, freshwater fish, taxonomy
Myloplus Gill, 1896 comprises large Serrasalmidae fishes that can reach up to 475 mm standard length (
Three species are recognized within the genus Myloplus according to the morphological concept of
From the material collected in the Rio Madeira Basin, Brazil, a previously undescribed species was identified by
Counts and measurements were performed as described by
The institutional abbreviations follow
Tometes
sp.:
Paratypes. All from Brazil. INPA 50868 (3 specimens 183.8–339.5 mm SL), collected with holotype. MPEG 30680 (1 specimen 351.1 mm SL), Mato Grosso, Aripuanã, downstream of Salto de Dardanelos, Rio Aripuanã, 10°09'46.5"S, 59°26'54.9"W, 12 December 2014, V. Machado. MPEG 30663 (1 specimen 244.5 mm SL), INPA 48546 (1 specimen 249.9 mm SL), and ZUEC 10776, (1 specimen 246.5 mm SL), Brazil, Amazonas, Novo Aripuanã, Parque Nacional dos Campos Amazônicos, Rio Roosevelt, Madeira Basin, 8°11'51"S, 60°58'19.2"W, October 2003, M. Camargo–Zorro & T. Giarrizzo.
Myloplus zorroi sp. n. can be distinguished from its congeners by the absence of abdominal keel and the prepelvic serrae formed by 13–19 low spines (Fig.
Morphometric data is presented in Table
Morphometric data of Myloplus zorroi (N = 8). Range values include the holotype. SD = standard deviation.
Holotype | Range | Mean | SD | |
---|---|---|---|---|
Standard length (mm) | 326.2 | 183.8–351.1 | 282.9 | * |
Percentages of standard length | ||||
Body depth | 59.3 | 59.1–62.5 | 60.4 | 1.3 |
Head length | 24.3 | 21.8–24.6 | 23.4 | 0.9 |
Supraoccipital process | 26.0 | 25.9–29.6 | 27.8 | 1.3 |
Predorsal length | 53.7 | 51.9–55.8 | 54.1 | 1.3 |
Dorsal-fin base length | 29.2 | 27.6–30.1 | 29.0 | 0.7 |
Interdorsal length | 12.1 | 11.4–12.7 | 12.1 | 0.5 |
Adipose-fin base length | 6.7 | 5.6–6.7 | 6.1 | 0.4 |
Caudal peduncle depth | 10.8 | 10.1–11.1 | 10.6 | 0.3 |
Anal-fin base length | 33.6 | 32.3–35.3 | 33.7 | 1.0 |
Preanal length | 77.6 | 72.5–79.1 | 76.9 | 1.9 |
Prepelvic length | 58.7 | 54.7–59.0 | 57.5 | 1.4 |
Prepectoral length | 24.6 | 23.5–25.3 | 24.5 | 0.6 |
Anal-pelvic distance | 21.5 | 21.2–24.0 | 22.6 | 1.0 |
Pelvic-pectoral distance | 36.1 | 32.3–36.1 | 34.1 | 1.4 |
Width of peduncle | 5.1 | 3.7–5.3 | 4.4 | 0.7 |
Pectoral-fin length | 20.4 | 19.1–20.9 | 20.2 | 0.6 |
Pelvic-fin length | 15.5 | 13.9–16.1 | 15.0 | 0.7 |
First anal-fin lobe length | 30.7 | 24.0–32.4 | 29.4 | 3.5 |
Second anal-fin lobe length | * | 13.9–18.2 | 15.4 | 2.4 |
Dorsal-fin length | 27.9 | 25.2–31.1 | 28.2 | 1.6 |
Distance dorsal-fin origin to anal-fin origin | 64.9 | 62.0–65.9 | 64.6 | 1.1 |
Distance dorsal-fin end to anal-fin origin | 49.0 | 46.9–49.6 | 48.5 | 0.9 |
Distance dorsal-fin end to anal-fin end | 26.0 | 24.1–26.7 | 25.3 | 0.8 |
Percentages of head length | ||||
Snout length | 31.2 | 29.3–33.7 | 31.4 | 1.4 |
Interorbital width | 53.8 | 49.2–56.5 | 53.0 | 2.7 |
Head width | 66.8 | 64.9–71.1 | 68.4 | 2.3 |
Postorbital distance | 34.2 | 32.8–36.6 | 34.0 | 1.2 |
Fourth infraorbital width | 16.2 | 14.6–19.6 | 16.9 | 1.4 |
Eye vertical diameter | 27.4 | 27.3–35.4 | 30.9 | 2.9 |
Mouth length | 17.6 | 14.4–18.2 | 16.9 | 1.4 |
Third infraorbital width | 11.8 | 11.8–14.1 | 12.9 | 0.8 |
Cheek gap width | 9.9 | 9.2–12.6 | 11.1 | 1.1 |
Mouth width | 36.1 | 31.7–38.5 | 35.9 | 2.0 |
Snout gently rounded, mouth terminal, slightly oriented dorsally; jaws equal in size. Labial row of premaxillary teeth separated from lingual row by a gap; five teeth in labial row and two teeth in lingual row (Fig.
Myloplus zorroi, a new species from Rio Roosevelt, Madeira Basin. Paratype, ZUEC 10776, male, 246.5 mm SL. A Premaxilla in ventral view, molariform teeth, labial and lingual rows interspaced B Dentary view C Premaxilla in lateral view. 1–5: Labial row of premaxillary teeth; 1'–2': Lingual row of premaxillary teeth; gap: Gap between the labial and lingual rows of the premaxillary teeth; sy: Symphyseal tooth; pmx: Premaxilla; ap: Ascending process of the premaxilla. Dashed line: premaxilla contour. Scale bar: 1 mm.
Scales cycloid, lateral line with 80 (1), 81 (3), 82 (2), or 83* (2) perforated imbricate scales from supracleithrum to hypural joint; total perforated scales 85 (1), 86 (2), 87 (1), 88* (2), or 89 (2). Scale rows between dorsal-fin origin and lateral line 39 (1), 40* (3), 41 (2), or 42 (2). Scale rows between lateral line and pelvic-fin insertion 36 (2), 38* (2), 39 (2), 40 (1), or 42 (1). Circumpeduncular scales 34 (1), 35* (3), or 36 (4). Prepelvic serrae with 13 (1), 17 (2), 18 (2), or 19* (3) very reduced spines (Fig.
Pectoral-fin rays i, 16 (2), i, 17 (5), or i, 18* (1). Pelvic-fin rays i, 7* (7), or i, 8 (1). Dorsal-fin origin at midbody preceded by strong forward-directed spine. Dorsal-fin rays ii* (4), or iii (4), and 20 (3), 21* (4), or 22 (1); anteriormost rays longest. Anal-fin rays iii (7), or iv* (1), and 32 (3), 33* (2), or 34 (3). Adipose fin with sub-rectangular distal margin. Caudal fin forked into lobes of similar size.
Total vertebrae 40 (1), or 41 (2). Predorsal vertebrae 10 (3). Postdorsal vertebrae 15 (2), or 16 (1). Vertebrae through last dorsal-fin pterygiophore and first anal-fin pterygiophore 2 (1), or 3 (2). Supraneurals 6 (3). Neurocranium in lateral view high, short, triangular, with concavity at epiphyseal bar level. Ascending process of premaxilla broader from its base to tip, with slightly rounded edge (Fig.
Color in alcohol. Ground coloration silver brownish to yellowish silver, with pale hues. Darker coloration on humeral region. Overall pigmentation of head above eye somewhat darker than that of adjoining areas. Body more yellowish postero-ventrally on anal-fin region. Darker blotches, irregular in size and shape, scattered on the flanks (Fig.
Color in life. Based on photos of specimens collected by sport fishermen at Rio Aripuanã, M. zorroi sp. n,. has ground coloration reddish silver, inconspicuous darker marks distributed on flanks, dorsum and head more darkened, and belly pale yellow. Dorsal, adipose, anal, and caudal fins yellowish brown.
Sexual dimorphism. The main secondary feature in mature males of Myloplus zorroi sp. n. is the additional anal-fin lobe centered on the 14th branched ray (Fig.
Myloplus zorroi is known from Aripuanã and Roosevelt rivers, two tributaries of the Rio Madeira basin (Fig.
The type locality of Myloplus zorroi is a moderately to rapidly flowing, clear-water river running over rocky and sandy bottoms (Fig.
The specific name ‘zorroi’ is dedicated to Mauricio Camargo-Zorro, a researcher at the Instituto Federal de Educação, Ciência e Tecnologia, in recognition of his invaluable contribution to the fish fauna inventory from the Marmelos Conservation Area. The name ‘zorroi’ also alludes to the Latin-American fictional character ‘Zorro’, which was the secret identity of Don Diego de la Vega, because the special features “masked” this fish as Tometes, concealing its true identity.
Myloplus zorroi differs markedly from its congeners in having a rounded abdominal region that lacks a marked keel and has a low number of small spines forming the prepelvic serrae (Fig.
Myloplus zorroi was incorrectly classified as an unknown species of the genus Tometes by
Several classifications of Myloplus have been proposed.
Myloplus arnoldi:
The authors would like to thank Lúcia Rapp Py-Daniel, Renildo Oliveira, and Douglas Bastos (INPA), Valéria Machado (UFAM), Wolmar Wosiacki and Izaura Magalhães (MPEG), Cecile Gama (