A new species of barred <i>Sternopygus</i> (Gymnotiformes: Sternopygidae) from the Orinoco River

Torgersen, Kevin T.; Galindo-Cuervo, Aleidy M.; Reis, Roberto E.; Albert, James S.

doi:10.1590/1982-0224-2022-0088

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Original Article • Neotrop. ichthyol. 21 (1) • 2023 • https://doi.org/10.1590/1982-0224-2022-0088 copy

A new species of barred Sternopygus (Gymnotiformes: Sternopygidae) from the Orinoco River

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

A new species of Sternopygus is described from the Orinoco River of Venezuela using traditional methods of morphometrics and meristics, and micro-computed tomography (micro-CT) imaging for osteological analysis. The new species is readily separated from all congeners in having broad, vertical pigment bars that extend from the mid-dorsum to the ventral margin of the pterygiophores. A similar color pattern, characterized by subtle differences in the densities and sizes of chromatophores, is also present in juveniles of S. obtusirostris from the Amazon River, juveniles of S. sabaji from rivers of the Guiana Shield, and S. astrabes from clearwater and blackwater terra firme streams of lowlands around the Guiana Shield. The new species further differs from other congeners in the Orinoco basin by having a reduced humeral pigment blotch with poorly defined margins, a proportionally smaller head, a longer body cavity, a more slender body shape in lateral profile, and in having vertical pigment bars that extend ventrally to the pterygiophores (vs. pigment saddles not reaching the pterygiophores). The description of this species raises to three the number of Sternopygus species in the Orinoco basin, and to 11 the total number of Sternopygus species.

Keywords:
Biodiversity; Computed tomography; Knifefish; Morphometrics; Taxonomy

Sociedade Brasileira de Ictiologia Neotropical Ichthyology, Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá., Av. Colombo, 5790, 87020-900, Phone number: +55 44-3011-4632 - Maringá - PR - Brazil
E-mail: neoichth@nupelia.uem.br

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[1] Edited-by

William Crampton

Species	Holotype	Type drainage (Country)
Sternopygus aequilabiatus (Humboldt, 1805)	Whereabouts unknown	Magdalena (Colombia)
Sternopygus arenatusEydoux & Souleyet, 1841	MNHN 0000-3809 (2 syntypes)	Guayaquil (Ecuador)
Sternopygus astrabesMago-Leccia, 1994	MBUCV-V-14182	Orinoco (Venezuela)
Sternopygus brancoCrampton, Hulen & Albert, 2004	MCP 32451	Amazonas (Brazil)
Sternopygus dariensisMeek & Hildebrand, 1913	FMNH 8949	Tuira (Panama)
Sternopygus macrurus(Bloch & Schneider, 1801)	ZMB 8701 (syntype, stuffed)	Unknown (Brazil)
Sternopygus obtusirostrisSteindachner, 1881	MCZ 9413 (lectotype)	Amazonas (Brazil)
Sternopygus pejeraton Schultz, 1949	USNM 121752	Maracaibo (Venezuela)
Sternopygus sabaji Torgersen & Albert, 2022	ANSP 208090	Maroni (Suriname)
Sternopygus n. sp. (in this study)	ANSP 209718	Orinoco (Venezuela)
Sternopygus xingu Albert & Fink, 1996	MZUSP 48374	Xingu (Brazil)

Landmark	Description
1	Anterior margin of upper jaw at mid-axis of body
2	Center of eye
3	Nape at posterior margin of occipital crest
4	Urogenital pore
5	Posterior margin of bony opercle
6	Insertion of anal fin
7	Center of dorsum at 25% LEA
8	Ventral extent of pterygiophores at 25% LEA
9	Center of dorsum at 50% LEA
10	Ventral extent of pterygiophores at 50% LEA
11	Center of dorsum at 75% LEA
12	Ventral extent of pterygiophores at 75% LEA
13	End of anal fin

	LEA						AFL					CA %
Species	n		range		mean		n	range		mean		n		range		mean
Sternopygus sarae	40		166–340		219		40	145–303		192		40		8.5–45.7		27.9
Sternopygus aequilabiatus group	16		160–390		228		16	134–335		189		12		11.0–29.0		17.8
Sternopygus arenatus	6		195–455		329		6	153–380		261		4		10.9–23.1		17.1
Sternopygus astrabes	22		81–177		121		22	64–148		102		16		23.4–43.2		34.0
Sternopygus branco	13		171–353		265		13	141–309		231		13		24.4–41.3		32.9
Sternopygus macrurus	76		140–455		265		66	114–405		224		47		10.6–28.7		18.5
Sternopygus obtusirostris	16		167–520		291		16	120–465		252		10		9.0–25.1		15.7
Sternopygus sabaji	7		130–311		213		7	111–258		179		7		18.9–31.5		25.3
Sternopygus xingu	5		162–446		283		5	134–371		236		3		13.3–27.2		21.0
	HL						PO %					PR %
Species	n		range		mean		n	range		mean		n		range		mean
Sternopygus sarae	45		19.6–36.5		23.8		45	54.8–63.5		57.4		45		33.2–39.9		35.9
Sternopygus aequilabiatus group	16		23.5–55.8		34.2		16	55.9–60.0		58.7		16		30.6–36.0		33.1
Sternopygus arenatus	6		32.7–62.2		47.5		6	56.3–59.1		57.6		6		32.7–37.5		35.2
Sternopygus astrabes	22		11.2–23.4		16.0		22	48.2–59.5		54.2		22		28.9–35.5		32.7
Sternopygus branco	13		24.4–41.3		32.9		13	50.8–54.9		53.0		13		36.1–40.6		38.4
Sternopygus macrurus	66		18.2–63.0		37.8		66	51.6–60.8		56.5		66		30.8–39.3		36.1
Sternopygus obtusirostris	16		20.1–54.2		33.6		16	53.4–61.2		57.3		16		31.0–35.9		34.0
Sternopygus sabaji	7		19.9–48.2		30.3		7	55.2–57.0		56.1		7		34.5–37.1		36.0
Sternopygus xingu	5		26.3–75.6		49.3		5	54.7–59.3		56.7		5		31.9–33.9		33.0
	MW %						BO %					HD %
Species	n		range		mean		n	range		mean		n		range		mean
Sternopygus sarae	37		16.0–19.1		17.6		36	25.0–36.3		30.7		45		58.9–79.4		70.9
Sternopygus aequilabiatus group	16		11.1–16.8		13.2		16	20.0–27.8		23.8		16		59.5–67.7		62.0
Sternopygus arenatus	2		11.0–13.8		12.4		2	15.7–16.5		16.1		2		68.8–73.4		71.1
Sternopygus astrabes	22		12.8–20.9		15.5		22	28.9–48.0		37.1		22		66.4–77.4		72.3
Sternopygus branco	13		12.3–13.9		12.9		13	25.9–31.1		28.2		13		57.8–68.4		64.7
Sternopygus macrurus	66		13.4–21.4		16.8		66	25.4–50.0		31.3		66		64.8–80.2		71.3
Sternopygus obtusirostris	16		14.4–17.6		15.8		16	25.4–45.3		36.9		16		68.6–79.5		73.8
Sternopygus sabaji	7		19.4–23.4		20.8		7	27.0–31.9		29.7		7		60.7–74.6		70.3
Sternopygus xingu	5		17.1–19.8		18.5		5	35.2–51.4		42.1		5		65.3–75.7		69.1
	PCV						P1R					AFR
Species	n		range		median		n	range		median		n		range		median
Sternopygus sarae	10		24–26		24		44	14–16		15		41		278–325		302
Sternopygus aequilabiatus group	16		23–25		24		20	14–17		17		16		228–310		284
Sternopygus arenatus	6		21–24		21		9	15–17		15		1		215–215		215
Sternopygus astrabes	29		18–19		19		23	15–17		16		19		170–298		200
Sternopygus branco	12		25–27		26		13	12–15		13		12		250–340		278
Sternopygus macrurus	52		24–28		26		95	13–17		15		44		195–300		256
Sternopygus obtusirostris	14		22–26		25		20	15–15		15		14		195–312		285
Sternopygus sabaji	5		21–22		22		18	15–15		15		18		204–237		220
Sternopygus xingu	4		28–29		29		6	12–15		12		4		292–321		312
	BD %					BW %							HL %
Species	n	range		mean		n			range		mean		n		range		mean
Sternopygus sarae	41	8.8–10.7		9.9		41			3.9–5.4		4.7		41		9.9–12.2		10.9
Sternopygus aequilabiatus group	16	10.5–13.8		12.1		16			5.3–6.3		5.9		16		13.4–16.1		15.1
Sternopygus arenatus	2	12.4–13.3		12.9		2			5.8–5.9		5.9		6		13.2–16.8		14.6
Sternopygus astrabes	22	10.4–12.4		11.5		22			4.6–6.6		5.5		22		11.7–14.7		13.3
Sternopygus branco	13	8.3–10.9		9.3		13			4.2–6.4		4.5		13		11.4–14.3		12.6
Sternopygus macrurus	66	10.3–15.2		12.8		66			4.8–8.3		6.1		66		12.5–16.8		14.3
Sternopygus obtusirostris	16	9.5–12.2		10.6		16			3.9–6.0		4.7		16		10.4–12.7		11.7
Sternopygus sabaji	7	12.1–14.3		12.7		7			5.4–7.0		6.1		7		14.3–15.5		15.0
Sternopygus xingu	5	13.4–16.1		14.4		5			6.2–8.2		6.8		5		16.2–19.6		17.2
	ED %					IO %							NN %
Species	n	range		mean		n			range		mean		n		range		mean
Sternopygus sarae	45	6.7–10.6		8.3		45			27.5–37.6		30.5		45		12.7–18.0		16.1
Sternopygus aequilabiatus group	16	6.8–9.8		8.6		16			14.4–21.7		17.5		16		10.2–14.4		12.2
Sternopygus arenatus	2	7.4–9.8		8.6		2			22.4–33.0		27.7		2		7.4–9.8		8.6
Sternopygus astrabes	22	13.8–19.5		15.5		22			23.8–30.4		26.1		17		14.5–19.8		17.3
Sternopygus branco	13	9.8–13.5		10.7		13			22.2–25.7		24.2		13		14.9–17.4		16.0
Sternopygus macrurus	66	7.5–14.6		10.3		66			17.6–31.7		25.5		66		8.3–17.9		13.9
Sternopygus obtusirostris	16	10.1–13.5		11.9		16			22.7–28.3		24.9		16		13.5–20.0		16.9
Sternopygus sabaji	7	7.6–9.3		8.2		7			23.6–26.5		25.3		7		14.5–16.4		15.0
Sternopygus xingu	5	6.7–12.2		9.4		5			16.7–22.4		24.8		5		11.4–15.6		13.3
		HW %							PA %						P1 %
Species	n	range		mean		n			range		mean		n		range		mean
Sternopygus sarae	45	36.9–53.2		45.9		45			32.2–67.6		42.4		45		43.6–57.8		50.6
Sternopygus aequilabiatus group	16	35.9–44.6		38.8		16			40.1–56.3		47.0		16		43.7–53.3		48.8
Sternopygus arenatus	2	42.8–47.1		44.9		2			61.6–67.0		64.3		6		40.0–56.0		45.0
Sternopygus astrabes	22	37.5–51.9		46.4		22			14.3–52.6		39.4		22		43.6–67.8		58.0
Sternopygus branco	13	36.1–43.4		39.8		13			30.3–38.2		33.8		13		50.0–57.2		53.2
Sternopygus macrurus	66	33.5–59.4		46.7		66			32.7–65.1		47.6		64		37.8–64.7		48.6
Sternopygus obtusirostris	16	36.7–50.7		42.9		16			29.0–50.9		37.1		16		45.8–60.5		52.3
Sternopygus sabaji	7	39.9–47.8		43.5		7			29.9–53.2		41.2		7		44.1–52.4		47.6
Sternopygus xingu	5	38.8–47.3		43.4		5			32.7–42.4		36.6		5		36.8–43.0		39.7
	SAL					SBL							SOP
Species	n	range		median		n			range		median		n		range		median
Sternopygus sarae	7	15–20		18		7			9–13		11		7		19–22		20
Sternopygus aequilabiatus group	18	12–24		17		18			7–13		9		18		10–16		13
Sternopygus arenatus	6	15–16		16		6			7–9		8		6		15–16		16
Sternopygus astrabes	19	11–18		15		19			9–14		12		19		10–16		14
Sternopygus branco	10	17–26		19		10			13–17		16		10		13–20		17
Sternopygus macrurus	55	12–22		16		55			6–20		9		55		9–15		13
Sternopygus obtusirostris	18	15–21		18		18			7–13		11		18		14–19		17
Sternopygus sabaji	5	12–14		13		5			5–5		5		5		12–15		13
Sternopygus xingu	3	14–16		15		3			6–8		7		3		14–19		18

	Holotype	Min	Max	Mean	Median	N
TL	407	216	407	280	–	40
LEA	340	166	340	219	–	41
AFL	303	145	303	192.7	–	41
CA	68	17	86	60.6	–	40
BD	35.0	16.9	35.0	21.5	–	45
BW	18.5	7.1	18.5	10.2	–	45
HL	36.5	19.6	36.5	23.8	–	45
PO	21.2	11.4	21.2	13.7	–	45
PR	13.4	7.0	13.4	8.5	–	45
ED	2.7	1.6	2.7	2.0	–	45
IO	10.8	5.5	10.8	7.2	–	45
NN	5.7	3.1	5.7	3.8	–	45
MW	6.7	3.3	6.7	4.3	–	45
BO	11.4	4.9	11.4	7.4	–	36
HD	27.8	13.5	27.8	16.9	–	45
HW	19.4	7.7	19.4	11.0	–	45
PA	16.8	6.4	16.8	10.1	–	45
P1	16.5	9.3	16.5	12.0	–	45
PCV	24	24	26	–	24	10
P1R	15	14	16	–	15	44
AFR	308	278	325	–	302	41
SAL	20	15	20	–	18	7
SBL	13	9	13	–	11	7
SOP	19	19	22	–	20	7

Species	Lot	LEA	TR
S. astrabes	ANSP 162663	138	15.2%
S. astrabes	ANSP 162663	178	18.5%
S. astrabes	INHS 61503	106	16.8%
S. astrabes	INHS 61503	113	17.5%
S. astrabes	INHS 61503	121	17.1%
S. astrabes	INHS 61503	129	16.8%
S. astrabes	INHS 61503	138	15.8%
S. astrabes	INHS 61503	144	15.8%
S. astrabes	INHS 61503	155	16.1%
S. astrabes	INHS 61503	188	15.7%
S. macrurus	UF 80276	239	24.2%
S. macrurus	UF 80276	170	21.7%
S. macrurus	UF 80276	161	18.5%
S. obtusirostris	INPA 6430	508	25.0%
S. obtusirostris	MCP 32262	490	24.6%
S. sarae	ANSP 160357	187	20.3%
S. sarae	ANSP 160357	195	21.4%
S. sarae	ANSP 160357	208	20.4%
S. sarae	ANSP 160357	209	21.2%
S. sarae	ANSP 160357	225	20.2%
S. sarae	ANSP 160357	231	19.8%
S. sarae	ANSP 160357	235	20.8%
S. sarae	ANSP 160357	272	19.1%
S. sarae	ANSP 160357	310	20.0%
S. sarae	ANSP 209718	340	20.4%