Apteronotus anu, Santana & Vari, 2013

Santana, Carlos David De & Vari, Richard P., 2013, Brown ghost electric fishes of the Apteronotus leptorhynchus species-group (Ostariophysi, Gymnotiformes); monophyly, major clades, and revision, Zoological Journal of the Linnean Society 168 (3), pp. 564-596 : 570-574

APTERONOTUS ANU SP. NOV. ( FIGS 4 , 5 ; TABLE 1)

Apteronotus leptorhynchus (not of Ellis), Schultz, 1949: 69 [original description: Venezuela, Lago Maracaibo basin, Río San Juan, Río San Pedro, Río Negro]. – Galvis, Mojica & Camargo, 1997: 104, figs. [ Colombia, Lago Maracaibo basin, Río Catatumbo; habitat]. – Péfaur, 1988: 471 [ Venezuela, upper Andean areas]. – Albert, 2003: 498 [in part in listing of species; citations from Río Catatumbo]. – Lasso et al., 2004a: 181 [ Venezuela, Lago Maracaibo]. – Rodríguez-Olarte, Taphorn & Lobón-Cerviá, 2009: 67 [ Venezuela, Perija Andes].

Diagnosis: Apteronotus anu is distinguished from A. baniwa by the condition of the fifth infraorbital (present as a tubular laterosensory canal segment versus absent), the number of caudal-fin rays (10–13 versus 14–17), the condition of the lateral ethmoid (cartilaginous versus ossified), and the number of precaudal vertebrae (18–19 versus 16–17). Apteronotus anu is differentiated from A. ferrarisi by the condition of the fifth infraorbital (present as a tubular laterosensory canal segment versus absent), the condition of the lateral ethmoid (cartilaginous versus ossified), the number of scales above the lateral line at the midbody (seven to nine versus 10–13), the number of scales along the lateral line (59–63 versus 73–80), the number of caudal-fin rays (10–13 versus 15–17), the extent of the mid-dorsal groove (extending seven to eight scales beyond the vertical through the posterior terminus of the anal fin versus two to six), and the tail length (17.1–37.5% of LEA versus 6.9– KEY TO THE SPECIES OF APTERONOTUS LEPTORHYNCHUS SPECIES- GROUP

1a. Fifth infraorbital in form of externally obvious tubular laterosensory canal segment ( Fig. 3A ).......................2

1b. Fifth infraorbital absent ( Fig. 3B )....................................................................................................... 4

2a. Pectoral-fin rays 15–17; total anal-fin rays 137–164; posterior limit of mouth extending posteriorly distinctly beyond vertical through anterior margin of eye.....................................................................................3

2b. Pectoral-fin rays 12–13; total anal-fin rays 171–173; posterior limit of mouth falling short of vertical through anterior margin of eye................... Apteronotus spurrellii (Ríos Condoto and Dagua, Pacific slope of Colombia)

3a. Tail length 17.1–37.5% of LEA; caudal-fin rays 10–13.............................................................................. ................................................................. Apteronotus anu sp. nov. (Lago Maracaibo basin, Venezuela)

3b. Tail length 10.6–12.4% of LEA; caudal-fin rays 14–16.............................................................................. ......................................... Apteronotus rostratus (Río Magdalena, Río Cauca, and coastal rivers of Panamá)

4a. Tail length 11.3–24.3% of LEA; tail depth 6.8–19.0% of CL .....................................................................5

4b. Tail length 6.9–9.9% of LEA; tail depth 22.2–28.7% of CL........................................................................ ............................ Apteronotus ferrarisi sp. nov. (coastal Caribbean drainages of northernmost Venezuela)

5a. Scales above lateral line at midbody 7–10 ............................................................................................6

5b. Scales above lateral line at midbody 11–14...........................................................................................7

6a. Scales along lateral line 61–70; scales above lateral line at midbody 7–8; caudal-fin rays 14–17 ..................... ................................................................. Apteronotus baniwa sp. nov. (upper Río Orinoco, Venezuela)

6b. Scales along lateral line 74–83; scales above lateral line at midbody 9–10; caudal-fin rays 18–20.................... ........................... Apteronotus pemon sp. nov. (Techine-Meru waterfall, upper Río Caroni basin, Venezuela)

7a. Caudal-fin rays 18–21.......................................................................................................................8

7b. Caudal-fin rays 10–16......................................................................................................... Apteronotus galvisi (Ríos Cusiana, Cravo, Pauto, and Upia along piedmont of Cordillera Oriental, upper Río Meta, Colombia)

8a. Pectoral-fin rays 17–18; snout length in dimorphic male 41.9% of HL; mouth length in dimorphic male 48.8% of HL; branchial opening in dimorphic male 14.9% of HL ............................................................................ ...................................................................... Apteronotus leptorhynchus ( Essequibo River basin, Guyana)

8b. Pectoral fin-rays 15–17; snout length in dimorphic male 44.7% of HL; mouth length in dimorphic male 56.2% of HL; branchial opening in dimorphic male 12.1% of HL .... Apteronotus macrostomus (lower Río Meta, Colombia) 9.9%). Apteronotus anu differs from A. galvisi in the condition of the fifth infraorbital (present as a tubular laterosensory canal segment versus absent), the condition of the lateral ethmoid (cartilaginous versus ossified), the number of scales above the lateral line at the midbody (seven to nine versus 11–12), and the tail length (17.1–37.5% of LEA versus 11.8–15.9%). Apteronotus anu is distinguished from A. leptorhyn- chus by the condition of the fifth infraorbital (present as a tubular laterosensory canal segment versus absent), the condition of the lateral ethmoid (cartilaginous versus ossified), the number of scales above the lateral line at the midbody (seven to nine versus 12–13), the number of pectoral-fin rays (14–16 versus 17–18), the number of anal-fin rays (159–176 versus 151–156), the number of caudal-fin rays (10–13 versus 17–21), and the number of scales along the lateral line (59–63 versus 78–82). Apteronotus anu is differentiated from A. macrostomus by the condition of the fifth infraorbital (present as a tubular laterosensory canal segment versus absent), the condition of the lateral ethmoid (cartilaginous versus ossified), the number of anal-fin rays (159–176 versus 140– 152), the number of caudal-fin rays (10–13 versus 18–21), and the number of scales above the lateral line at the midbody (seven to nine versus 11–14). Apteronotus anu differs from A. pemon in the condition of the fifth infraorbital (present as a tubular laterosensory canal segment versus absent), the interorbital distance (14.7–36.5% of HL versus 9.7–14.6%), the number of caudal-fin rays (10–13 versus 18–20), the number of scales along the lateral line (59–63 versus 74–83), and the condition of the lateral ethmoid (cartilaginous versus ossified). Apteronotus anu is differentiated from A. rostratus by the tail length (17.1–37.5% of LEA versus 10.6–12.4%) and the number of caudal-fin rays (10–13 versus 14–16). Apteronotus anu is distinguished from A. spurrellii by the number of pectoral-fin rays (14–16 versus 12–13), the number of caudal-fin rays (10–13 versus 14), the number of scales along the lateral line (59–63 versus 73–76), the extent of the mid-dorsal groove (extending seven to eight scales beyond the vertical through the posterior terminus of the anal fin versus four) and the tail length (17.1–37.5% of LEA versus 12.5–13.7%).

Description: Head, body, and fin shape and pigmentation illustrated in Figure 4 . Morphometrics for holotype and paratypes presented in Table 1. Body laterally compressed, greatest body depth located at, or slightly posterior to, abdominal cavity. Dorsal profile of body nearly straight. First perforated scale of lateral line located above pectoral-fin origin. Lateral line extending posteriorly to base of caudal fin. Scales along lateral line 59(6), 61(4), 62*(5), or 63(3). Scales above lateral line to mid-dorsal line at midbody 7(4), 8(9), or 9*(12).

Head laterally compressed, widest at opercular region and deepest at nape. Dorsal profile of snout and overall head nearly straight. Eye small, located laterally on head, and completely covered by thin membrane. Anterior naris located at end of small tube and close to tip of snout. Posterior naris ellipsoidal, without tube and positioned closer to tip of snout than to anterior margin of eye. Mouth inferior with rictus extending posterior of vertical through anterior border of eye. Branchial opening located at, or slightly posterior to, vertical through pectoral-fin insertion. Anus and urogenital papilla located posterior to vertical through eye; position not ontogenetically variable.

Pectoral fin elongate, with 14*(10), 15(10), or 16(5) rays. Anal-fin origin located at, or slightly anterior to, vertical through posterior margin of opercle. Unbranched anal-fin rays 12(5), 15(3), 20(2), 23(5), 25*(3), or 30(3). Total anal-fin rays 159(1), 160(1), 161(1), 162(2), 163*(2), 164(1), 165(1), 167(1), 170(1), 171(4), 172(1), 173(1), or 176(1). Tail compressed and short; ending in small, elongate caudal fin. Caudal-fin rays 10(10), 11(2), or 13*(6).

Origin of dorsal sagittal electroreceptive filament situated on posterior half of body. Filament inserted into narrow mid-dorsal groove extending 7*(13) or N, number of specimens; H, holotype. Range includes holotype.

Sexually dimorphic features for A. baniwa and A. ferrarisi are presented as two entries. First entry is for sexually dimorphic males with information for females and immatures in second entry.

8(5) scales posterior to vertical through posterior terminus of anal-fin base. Precaudal vertebrae 18(3), 19*(2). Total vertebrae 70(2), 73*(2) or 83(1).

Coloration in life: Galvis et al. (1997: 104) provided a life photo of A. anu (identified in that paper as A. leptorhynchus ), which shows the head and body to be dark brown from a lateral view with the fins apparently hyaline.

Coloration in alcohol: Body and head light brown to black. Prominent pale, broad, longitudinal band extends from chin along dorsal midline of head and body to over dorsal filament. Pectoral and anal-fin rays ranging from translucent to dark brown. Interradial membranes translucent. Pale band encircling base of caudal fin. Caudal fin pale at base, pale to black on central portion and translucent posteriorly.

Distribution: Apteronotus anu is known from several rivers draining into Lago Maracaibo in north-eastern Colombia and north-western Venezuela ( Fig. 5 ). The apparent restriction of this species to the rivers draining that basin conforms to a pattern general in the Lago Maracaibo ichthyofauna in which two-thirds of the freshwater fish species in the basin are endemics ( Rodríguez-Olarte et al., 2009: 87).

Habitat: According to Galvis et al. (1997: 104), A. anu (identified in that study as A. leptorhynchus ) occurs in swift current habitats over substrates of rounded stones in the portion of Río Catatumbo in Colombia. Their observations indicate that A. anu is a voracious nocturnal predator. Péfaur (1988: 474) reported that the species (identified by him as A. leptorhynchus ) occurs at elevations of over 500 m asl in the Río Chama, a tributary to Lago Maracaibo.

Etymology: The species name, anu , is in reference to the Añu indigenous peoples who lived along the shores of Lago Maracaibo in traditional houses termed Palafitos, which they built above the lake. Such housing reminded early European explorers of Venice, Italy, and may have been the basis for the application of the name Venezuela to the region.

Remarks: Apteronotus anu is trenchantly differentiated from A. spurrellii , one of two other species of the A. rostratus clade, in the numbers of pectoral- and total anal-fin rays in addition to the position of the posterior limit of the mouth. Apteronotus anu and A. rostratus , the other member of the clade, are not separated to a comparable degree, but differ in the length of the tail (17.1–37.5% of LEA versus 10.6–12.4%, respectively) and in the number of caudal-fin rays (10–13 versus 14–16). The results of the PCA showed separation between A. anu and A. rostratus along the first and second principal components (PC1 and PC2; Fig. 6 ). PC1 and PC2 reflected 89.7 and 3.8%, of the variation respectively. The best predicators of the differences between the two species were: the distance from the posterior snout to the eye (0.38), the mouth length (0.30), and the internarial distance (0.89). A jackknife cross-validation procedure correctly classified 100% of the specimens by species, further supporting the hypothesis of the differences of A. anu and A. rostratus .

As noted in the Introduction, samples of the A. leptorhynchus clade from across vast expanses were identified as A. leptorhynchus in the prior literature. Populations previously identified as A. leptorhynchus by Schultz (1949: 69), Galvis et al. (1997: 104), Péfaur (1988: 471), Lasso et al. (2004a: 181), and Rodríguez-Olarte et al. (2009) based on samples originating in various rivers draining into Lago Maracaibo in both Colombia and Venezuela were found here to be A. anu based on the collecting localities.

Material examined: Holotype: Venezuela. Zulia. MCNG 24991 , holotype, 132; Rio Negro, 12 km south of Machiques on way to Tokuko at the bridge, Taphorn et al., 1.viii.1991.

Paratypes: Venezuela. Mérida. INHS 34978 , 1 , 231 ; Rio Chama , Lago Maracaibo, El Vigia, 08°25′54′′N, 71°37′31′′W, 31.i.1995. INHS 59885 , 1 , 174 ; tributary of Río Gavilan, Lago Maracaibo basin, 3 km east of Capazon , 08°49′04″N, 71°25′03″W, 6.i.1991. Zulia. INHS 35364 , 16 , 35–118 , Caño Taguara, Rio Santa Ana, Lago Maracaibo basin, 18 km north of Puerto Catatumbo along highway at bridge, 09°17′22′′N, 72°32′49′′W, 2.ii.1995. INHS 35443 , 1 , Río Santa Ana , Lago Maracaíbo basin, bridge approximately 8 km south-west of Alturistas, 09°41′30′′N, 72°25′47′′W. INHS 59949 , 1 , 182 ; Rio Negro, Río Santa Ana, Lago Maracaibo basin, 12 km south of Machiques on road to Tucuco, collected 8.i.1991. INHS 60284 , 6 , 90–115 ; Caño off Río Zulia, Lago Maracaibo basin, 12 km south of intersection of Highways 2 and 6, 8.i.1991. INHS 60468 , 1 , 117 , Río Yasa, Río Palmar, Lago Maracaibo, 5 km south of Machiques on road to Tucuco, 9.i.1991. MCZ 52023, 1 c&s, 149; Río San Juan, near bridge south of Mene Grande, Río Motatán basin, 09°49′N, 56°00′W, 17.iii.1942. USNM 121592 , 1 , 60 ; Río San Juan 12 km south of Rosario , Lago Maracaíbo basin, 26.ii.1942. USNM 121593 , 3 , 97–147 ; Río San Pedro at bridge, tributary of Río Motatán , Lago Maracaíbo basin, 20.iii.1942. USNM 121595 , 6 , 112–175 ; Río San Juan, near bridge close to Mene Grande, tributary of Río Motatán , Lago Maracaíbo basin, 17-20.iii.1942 .

Figures

Figure 3. Left lateral view of anterior and central portions of head of: A, Apteronotus anu, 132 mm total length (TL), holotype, MCNG 24991. A and B on figure positioned proximate to paths indicated in black of laterosensory canal segments in infraorbitals 6 and 4, respectively. Note presence of fifth infraorbital in form of paler tubular laterosensory canal segment between pores as indicated by white arrow; B, Apteronotus pemon, 165 mm TL, FMNH 70012. A and B on figure positioned proximate to paths indicated in black of laterosensory canal segments in infraorbitals 6 and 4 respectively. Note absence of tubular fifth infraorbital and associated pores between those canal segments.

Figure 4. Apteronotus anu, 132 mm total length, male, holotype, MCNG 24991; Venezuela, Maracaibo, Rio Negro, at bridge, 12 km south of Machiques on road to Tokuko.

Figure 5. Map of north portion of South America showing geographical distribution of Apteronotus anu (1 = holotype locality); Apteronotus baniwa (2 = holotype locality); Apteronotus ferrarisi (3 = holotype locality); Apteronotus galvisi (4 = holotype locality), and Apteronotus leptorhynchus (5 = holotype locality). Some symbols represent more than one locality and/or lot of specimens.

Figure 6. Principal components analysis on covariance matrix of log-transformed measurements of Apteronotus anu (squares) and Apteronotus rostratus (circles). Scatter plot of scores on first (PC1) and second (PC2) principal components.