Hypopygus ortegai, De Santana & Crampton, 2011

De Santana, Carlos D. & Crampton, William G. R., 2011, Phylogenetic interrelationships, taxonomy, and reductive evolution in the Neotropical electric fish genus Hypopygus (Teleostei, Ostariophysi, Gymnotiformes), Zoological Journal of the Linnean Society 163 (4), pp. 1096-1156 : 1148-1149

HYPOPYGUS ORTEGAI SP. NOV.

(FIGS 23C, 30; TABLE 5)

Stegostenopos cryptogenes : – Crampton & Albert, 2006: 672, figure 23.8 [Amazon basin, photograph of head, with EOD waveform].

Diagnosis: Hypopygus ortegai is diagnosed from congeners by the following combination of characters: the dorsal rami of intermittent branch of anterior lateral line nerve not visible (versus visible in remain Description: Head and body shape, and pigmentation illustrated in Figures 23C and 30. Morphometric data for examined specimens are presented in Table 5. Body size moderate, maximum examined length 126 mm (N = 114). Maximum examined length from snout to end of BC 21.3 mm. No sexual dimorphism in body or head shape. Snout slightly convex. Upper jaw slightly longer than lower jaw. Pectoral-fin rays 11–12 [11] (N = 7). Postpectoral EO with two columns and four rows of electrocytes. EO dorsal groove extending approximately one to two orbital diameters before posterior border of eye. Scales present on mid-dorsal region of body. Scales above lateral line at midbody three to five [five] (N = 7). Scales below lateral line six to seven [six] (N = 7). Total anal-fin rays 137–156 [156] (N = 7). Caudal filament moderate. Precaudal vertebrae 15 (12 anterior; three transitional; N = 1).

Pigmentation ( Fig. 30 and Fig. 23C for colour of live specimen): Body background dark brown. Light tan oblique bands from nape to end of caudal filament (14–17 crossing dorsal region of body, counting from nape to last anal-fin ray). Head dark brown. Prominent series of more or less regularly spaced inverted U-shaped dark spots over pterygiophores, at margin of anal fin, separated by light margins. Pectoral-fin ray and inter-radial membrane hyaline. Anal-fin ray and inter-radial membrane hyaline.

Electric organ discharge: Data available from eight specimens in type series, from the vicinity of Jenaro Herrera , Loreto, Peru. Hypopygus ortegai generates a tetraphasic EOD ( Fig. 17 ) ranging in duration from 1.17 to 2.11 ms (mean 1.73, N = 7), and with a PPF ranging from 1.408 to 1.869 kHz (mean 1.661, N = 7). Mean pulse rate during the day ranges from 44.7 to 56.8 Hz (mean 50.3, mean CV 0.91, N = 8), and during the night from 59.2 to 65.5 Hz (mean 62.1, mean CV 2.87 , N = 8) .

Distribution: Hypopygus ortegai is known from small tributaries in the upper Amazon of Peru, near the towns of Iquitos and Jenaro Herrera, Loreto ( Fig. 28 ).

Ecology: Hypopygus ortegai occurs in small rainforest creeks – primarily in dense mats of tree roots along the edge of streams, especially in undercut banks. Stomach contents (N = 5) included a variety of autochthonous aquatic invertebrates – mostly larvae of Chironomidae, Trichoptera, Coleoptera, and Ephemeroptera , and some remains of small shrimps. Hypopygus ortegai occurs syntopically with H. lepturus . Whereas H. lepturus is found in groups of up to several dozen individuals, H. ortegai is usually only found in groups of no more than three or four individuals. Additionally, whereas H. lepturus is found in streams both under rainforest canopy and in open areas (e.g. cleared farmland), H. ortegai is restricted to streams under dense forest canopy.

Etymology: The specific epithet, ortegai , is a patronym in honour of the Peruvian ichthyologist Hernán Ortega Torres, for his many contributions to Neotropical ichthyology and for his participation in the expedition that discovered this species.

Remarks: Specimens of H. ortegai are unique amongst species of Hypopygus in having the third basibranchial ossified. Hypopygus ortegai is also the largest species of the genus. Although its maximum body length (126 mm) is exceeded by H. cryptogenes (150 mm, largely because of a very long caudal filament), its maximum live weight (3.6 g) exceeds by more than twofold the maximum live weight of all congeners (c. 1.5 g).

Material examined: (114 specimens.)

Holotype. Peru, Loreto, MUSM 35305, 107 mm ( WC02.160104 , female); unnamed stream, 2 km north of km 3.9 on road from Jenaro Herrera to Colonia Angamos, 04°53′01″S, 073°38′10″W; W. Crampton, R. Reis, F. Lima, H. Ortega. 16.i.2004.

Paratypes. Peru, Loreto. MUSM 35306 , 2, 101–114 mm ( WC02.130104 , female, 114 mm; WC03.130104, female, 101 mm); Quebrada Sapuenillo, c. 7 km E Jenaro Herrera on road from Jenaro Herrera to Colonia Angamos , Río Ucayali drainage, 04°54′26″S, 073°36′44″W; W. Crampton, R. Reis, F . Lima, H. Ortega, 13.i.2004. MUSM 38677 , 2 , 71–73 mm ( WC46.110709 , immature, 73 mm; WC47.110709, immature, 71 mm); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°53′35″S, 073°39′06″W; W. Crampton, E. Correa, M. Aldea Guevara, J. Waddell, 11.vii.2009. MUSM 38678 , 1 , 65 mm ( WC01.120709 ); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°52′42″S, 073°38′51″W. W. Crampton, E. Correa, M. Aldea Guevara, J. Waddell; 12.vii.2009. MUSM 38679 , 5 , 56–75 mm ( WC01.140709 , immature, 67 mm; WC02.140709, 71 mm, immature; WC04.140799, 70 mm, immature; WC13.140709, 56 mm, immature; WC14.140799, 75 mm, immature); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°52′24″S, 073°38′49″W; W. Crampton, E. Correa, M. Aldea Guevara, J. Waddell, 14.vii.2009. MUSM 38680 , 8 , 73–79 mm ( WC01.160709 , 77 mm, immature; WC02.160709, 73 mm, immature; WC03.160799, 76 mm, immature; WC04.160709, 75 mm, immature; WC05.160709, 76 mm, immature; WC06.160709, 79 mm, immature; WC.08160799, 77 mm, immature); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°52′45″S, 073°38′51″W; W. Crampton, E. Correa, M. Aldea Guevara, J. Waddell, 16.vii.2009. UF 148458, 1 73 mm ( WC23.090104 , immature); stream in forest c. 2 km north of Instituto de Investigaciones de la Amazonia Peruana ( IIAP) field station (2.7 km east of Jenaro Herrera ), c. 04°53′S, 073°39′W; W. Crampton, R. Reis, F . Lima, H. Ortega, 9.i.2004. UF 148524, 6 , 83–118 mm (2 CS) [4 recorded: WC01.160104, immature, 92 mm ( CS); WC03.160104 , male, 118 m TL; WC04.160104, immature, 89 mm; WC05.160104, female, 98 mm]; same collecting data as holotype .

Nontypes. Peru, Loreto. ANSP 167730 , 1 , 75 mm; Río Nanay, brook crossing left trail c. 20 min walk from Mishana, Río Nanay drainage, 05°53′S, 073°27′W . UF 176879, 1, 101 mm ( CS); Río Nanay, 50 km 250° from Iquitos , 03°53′50″S, 073°40′01″W . MUSM 38681 , 3 , 75–82 mm (3 recorded for EODs); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°54′26″S, 073°36′44″W . MUSM 38682 , 1 , 49 mm (1 recorded for EODs); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°54′40″S, 073°39′29″W . MUSM 38683 , 2 , 84–103 mm (2 recorded for EODs); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°53′54″S, 073°38′23″W . MUSM 38684 , 3 , 77–78 mm (3 recorded for EODS); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°54′15″S, 073°36′53″W . MUSM 38685 , 8 , 73–87 mm (8 recorded for EODs); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°54′26″S, 073°36′44″W . MUSM 38686 , 69 , 62–126 mm (69 recorded for EODs); forest stream near Jenaro Herrera , Río Ucayali drainage, 04°52′33″S, 073°38′13″W .

Figures

Figure 17. Electric organ discharges (EODs) of Hypopygus as time-voltage waveforms recorded in the far-field. The EODs were in all cases taken from immature specimens or females with adult morphology, and are representative of most individuals of each species (small juveniles and sexually mature males present EODs that in some cases differ from those of larger juveniles, immature adults, and females). A, Hypopygus cryptogenes, INPA uncatalogued, 80 mm (poor signal recording quality). B, Hypopygus isbruckeri, UF 148537 (WC38.150304), immature, 76 mm. C, Hypopygus lepturus, UF 176883 (WC21.090307), female, 92 mm. D, Hypopygus minissimus, UF 148533 (WC41.120304), female, 42 mm. E, Hypopygus neblinae, UF 148540 (WC36.150304), female, 77 mm. F, Hypopygus nijsseni MCP 44740 (WC01.070703), immature, 70 mm. G, Hypopygus ortegai, MUSM 35305, holotype (WC02.160104), female, 107 mm. Scale bars = 1 ms. Dashed horizontal line = 0 volts. Note that all species generate EODs with a similar four- or five-phase structure, with minimal interspecific variation in duration (except in H. neblinae where the EOD is clearly longer).

Figure 28. Map of northern South America showing collection records of Hypopygus neblinae (circles), Hypopygus nijsseni (squares), and Hypopygus ortegai (triangles). Some symbols represent more than one nearby collecting locality.

Figure 30. Hypopygus ortegai, holotype, head, and lateral and dorsal views of body, 107 mm, MUSM 35305 (WC02.160104, female); Peru, Loreto, small unnamed stream, 2 km north of km 3.9 on road from Jenaro Herrera to Colonia Angamos, 04°53′01″S, 073°38′10″W, Loreto, Peru. Scale bars = 5 mm.