Gymnotus chaviro, Maxime & Albert, 2009

Maxime, Emmanuel L. & Albert, James S., 2009, A new species of Gymnotus (Gymnotiformes: Gymnotidae) from the Fitzcarrald Arch of southeastern Peru, Neotropical Ichthyology 7 (4), pp. 579-585 : 580-584

Gymnotus chaviro , new species

Figs. 1- 2

Holotype. MUSM 33715, 233 mm. Peru, Dept. Ucayali, Quebrada Dos y medio, a small terra firme stream ca. 2 km NW the town of Breu, on the Alto Yuruá River , 09°31.175S 72°45.755W, 271 m elevation, 20 Jul, 2008, J. S. Albert, R. Quispe & I. Corahua.

Paratypes. Peru, all collected with holotype : MUSM 33714 , 40 , 4 c&s, 95-275 mm ; FMNH 118274 , 10 , 134- 179 mm ; CAS 227893 , 10 , 123- 150 mm ; MCZ 168419 , 10 , 115- 160 mm ; MCP 43880, 10 , 116- 164 mm ; MZUSP 103035 , 10 , 130- 217 mm ; AMNH 248884 , 10 , 104- 180 mm .

Nontype specimens. All from Peru. MUSM 1406 , 1, 127 mm, Madre de Dios, Parque Nacional Manú, Quebrada Pabitza, Aguajal. MUSM 1759 , 2 , 142- 150 mm, Madre de Dios, Puerto Maldonado ,

river near Tambopata, Cochachica. MUSM 21405 , 1, 138 mm, Madre de Dios. MUSM 22731 , 10 , 2 c&s, 143-210 mm, Madre de Dios drainage. MUSM 16662 , 1, 325 mm, Madre de Dios, Tambopata, Madre de Dios drainage, lago Copamanu .

Diagnosis. Gymnotus chaviro is unique among members of the G. carapo group (sensu Albert et al., 2004) in having a color pattern composed of oblique, dark, unbroken pigment bands along the length of the body, dark band-pairs with wavy, irregular margins, mainly unbranched or incompletely separated, pale inter-bands rarely reaching to the dorsal midline on the anterior half of the body and crescent-shaped in abdominal area.

Gymnotus chaviro can further be distinguished from all congeners by the following unique combination of morphometric and meristic traits: 1, 17-22 oblique bands (vs. 24-26 in G. chimarrao ); 2, clear (unpigmented) patch of membrane at the caudal end of the anal-fin in specimens (vs. even pigmentation in G. cylindricus and G. pantherinus groups, or striped in G. tigre group); 3, anal fin pale gray (vs. black in G. carapo , G. arapaima , G. ucamara ); 4, several (4-5) arrow-head shaped teeth at anterior end of the dentary (vs. all conical in G. cylindricus and G. pantherinus groups, or five or more in most members of G. carapo group); 5, body depth 6.3-10.2% TL (vs. 10.3-13.1% in G. sylvius ); 6, mouth width 35.5-52.5% HL (vs. 26.9-28.1 in G. diamantinensis ); 7, interorbital distance 37.9-49.2% HL (vs. 28.6-36.5% in G. arapaima and in G. choco ); 8, head depth 61.8-89.0% HL (vs. 54.4-61.8% in G. choco and G. sylvius ); 9, head width 58.5- 74.7% HL (vs. 51.1-51.3% in G. diamantinensis ); 10, pectoral fin length 45.8-66.8% HL (vs. 36.3-41.1 in G. diamantinensis ); 11, pectoral-fin rays 18-19 (vs. 13-17 in G. carapo , G. ucamara , G. sylvius , G. mamiraua , G. diamantinensis , G. choco , G. bahianus , G. arapaima , G. omarorum , G. chimarrao , vs. 20-22 in G. obscurus ); 12, pored lateral-line scales to first ventral ramus 48-52 (vs. 32-39 in G. mamiraua , 40-41 in G. bahianus , 40 in G. chimarrao , and 24-35 in G. omarorum ); 13, head length 8.9-12.0% TL (vs. 12.2-15.8% in G. arapaima and G. ucamara ); 14, number of ventral lateral-line rami 7-12 (vs. 16-37 in G. chimarrao and G. omarorum ); 15, anal-fin rays 228-280 (vs. 180-213 in G. chimarrao and G. tigre ); 16, caudal rows of electroplates 4 (vs. 3 in G. diamantinensis and G. choco ); and 17, number of scales above the lateral line 7-9 (vs. 6 in G. ucamara ).

Gymnotus chaviro is most similar in external appearance to G. curupira from the western Amazon, from which it may be distinguished by the presence of two (rarely one) pores in the dorsoposterior corner of preopercle (vs. always one pore), fewer total pored lateral-line scales 86-100 (vs. 104-140), fewer pored lateral-line scales to the first ventral ramus (48-52 vs. 59-62), more pectoral-fin rays (18-19 vs. 16-17), and more electrocyte tubes (4 rows vs. 3) in the caudal region. Gymnotus chaviro is also similar in external appearance to G. varzea from the western Amazon from which it may be distinguished by more teeth on the dentary (16 vs. 11-12) and more teeth on the premaxilla (10 vs. 6-7). Gymnotus chaviro is also similar in external appearance to G. pantanal from Paraguay from which it may be distinguished by an incomplete separation of the dark pigment bands (vs. no separation), white interbands about as broad as dark bands (vs. no larger than one third), fewer dark bands (17-22 vs. 22-26), more scales over anal-fin pterygiophores (12-13 vs. 10-11), and fewer ventral lateralline rami (7-12 vs. 14-23).

Description. Morphometric and meristic data ( Table 2 ) were pooled from 89 specimens of type-series. Size up to 275 mm. No secondary sexual dimorphism observed in body shape or anatomy. Scales cycloid, ovoid, present on entire post-cranial portion of body from nape to tip of caudal appendage, large above lateral line small, over anal fin pterygiophores. Mouth superior, lower jaw extending beyond upper one, rictus decurved. Chin fleshy and bulbous with thick support tissues overlying tip of snout and oral jaws. Eyes below horizontal midline.Anterior narial pore pipe-shaped, located within gape. Anterior nares small, approximately 4-5 times smaller than diameter of eye. Gape never extended beyond posterior nares even in largest specimens. Posterior narial pore flush with head surface, circumorbital series ovoid.

Maxilla and palatine near tip of mesopterygoid. Maxilla oriented vertically, rod-shaped, narrow distally with a length of dentary portion bearing 7-9 tooth sockets. Premaxilla with two rows of teeth with few of them in outer row (less than 10), and curved median margin. Mandible short, dentary teeth flattened anteroposteriorly along long axis of oral margin of dentary grading to conical posteriorly, with 14 arrowheadshaped teeth in outer row and 10 in an anterior inner tooth patch. Ventroposterior hook-like process at mental symphysis. Opercular dorsal margin convex, its posterior margin smooth. Two closely-positioned laterosensory pores (rarely one) in dorsoposterior corner of preopercle, associated cutaneous laterosensory pores well separated. Ascending mesopterygoid process contacting orbitosphenoid, arched mediolateraly. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Hyomandibular posterior lateral-line foramen contacting posterior margin. Neurocranium with approximately triangular aspect in dorsal view, with narrow ethmoid region. Cranial fontanels closed. Mesethmoid anterior margin with paired anterolateral processes. Four tubes (rows) of electroplates at one HL distance from tip of caudal appendage. 37-38 precaudal vertebrae (including those of Weberian apparatus).

Coloration. Ground color yellowish. 17 to 22 (mode 20) oblique and non broken (or incompletely broken in largest specimen) pigment bands (gray) with irregular wavy margins on lateral surface extending from nape and pectoral-fin base to tip of caudal appendage and oriented either vertically or obliquely in an antero-ventral to postero-dorsal diagonal. Anterior most 2 to 3 pale interbands crescent-shaped. Majority of dark bands paired with pale middle region (intraband), dark bands approximately as wide as pale interbands. Dark bands above lateral line continuous on anterior half of body, not visible against dark ground color on dorsal midline. Pigment density greater at band margins than in middle. Band-interband contrast sharper caudally and bands thinner anteriorly. Most bands are not well divided, intraband formed by less density of pigments at the middle of the band, no sharp band-intraband contrast. Three to four dark bands meet irregularly at ventral midline in region anterior to anal-fin origin. Juveniles possess more regularly arrayed alternating pigment bands with sharper band-interband contrast.

Head never banded, spotted or blotched, strongly countershaded with dense speckling dorsally fading to pale yellow ventrally. No rosy hue visible to operculum from underlying gills in juveniles. Pectoral-fin rays and interradial membranes uniform light gray. Anal fin membrane never blotched, spotted or marked. Anal fin membrane lightly and evenly pigmented with scattered chromophores along most of its length, fading to an absence of chromophores caudally.

Preservational artifacts. After capture specimens were either fixed immediately in 10% unbuffered formalin, or transported live to a field base in buckets for processing (i. e., photography and tissue sampling) before fixation. Some differences in coloration and superficial appearance were observed among specimens subjected to these different preservational treatments. Specimens fixed immediately after capture exhibit the following traits: 1, pigments bands with high contrast dark brown ground color and yellow interbands (vs. low contrast); 2, body surface (skin of head and scales) lighter and more reflective due to a thicker mucous layer, scale margins less visible; 3, head orientation straight (vs. recurved or arched); 5, laterosensory pores small, their margins flush with surrounding body surface (vs. large with bulging margins); 6, lens black (vs. hyaline), Specimens subjected to different preservational treatments did not differ in morphometric, meristic or osteological traits, or in the diagnostic aspects of coloration.

Geographic distribution. The type series of Gymnotus chaviro is known from the upper Yuruá basin, Department Ucayali, Peru ( Fig. 3 ) and the Manu and Tampobata rivers of the Madre de Dios basin, Department Madre de Dios, Peru .

Ecological notes. Gymnotus chaviro inhabit pools and runs of small terra firme streams as they enter the floodplain, and the vegetated margins of flooplain lakes, with substrates of leaf litter and organic rich mud. Specimens are most dense in submerged stems and roots of aquatic grasses (e. g., Oryza spp.) and floating macrophytes (e. g., Eichornia crassipes ). At the period of low water (August) when collections were made, specimens were very abundant, aggregated closely together, and were not distributed into discrete territories. The holotype was collected in a small terra firme stream (1.2 m deep, 2.5 m wide, 25°C) with a muddy bottom and deeply undercut banks, about 1 km from the edge of the floodplain.

Local Name. Anguilla, Spanish for eel.

Etymology. From the common name for Gymnotus in the language of the Asheninka indigenous people (Arawak/ Maipurean language family). A noun in apposition.

Remarks. Types specimens were restricted to localities in the Yuruá basin. Specimens from the Manu and Tampobata basins are excluded from the type series.

Comparative examined material. Materials examined are listed in Campos-da-Paz & Costa (1996), Albert (2001), Albert & Crampton (2001, 2003), Campos-da-Paz (2002), Crampton et al. (2003, 2005), Maldonado-Ocampo & Albert (2003), Fernandes et al. (2005), Cognato et al. (2007), and Richer-de- Forges et al. (2009).

Figures

Fig. 1. Gymnotus chaviro, holotype, MUSM 33715, 233 mm TL. (a) head, (b) body. Scale bars = 20 mm.

Fig. 2. Gymnotus chaviro, paratype, MUSM 33714, 150 mm TL. (a) head, (b) body. Scale bars = 10 mm.

Fig. 3. Map of part of South America showing the known geographic distribution of Gymnotus chaviro. Type locality indicated by square symbol. Base map by M. Weitzman.