Brachyhypopomus diazi (Fernández-Yépez, 1972), , 1972

Crampton, William G. R., Santana, Carlos D. de, Waddell, Joseph C. & Lovejoy, Nathan R., 2016, A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species, Neotropical Ichthyology (e 150146) 14 (4), pp. 639-790 : 708-711

Brachyhypopomus diazi (Fernández-Yépez, 1972)

( Fig. 21 ; Tables 2-5, 11)

Hypopomus diazi Fernández-Yépez, 1972: 20 , pl. 20, black and white photograph of holotype (original description, type locality – Venezuela, Carabobo, río Alpargatón ).

Brachyhypopomus occidentalis . -Mago-Leccia, 1976 (systematics of Gymnotiformes , B. diazi listed as junior synonym of B. occidentalis ).

Brachyhypopomus diazi . -Mago-Leccia, 1994: 48, fig. 72, black and white photograph of MBUCV-V 13443 (listing of Brachyhypopomus ). - Sullivan, 1997: 137 (redescription). -Albert & Crampton, 2003: 495 ( Venezuela, listing of Brachyhypopomus ). - Crampton & Albert, 2006: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton, 2011: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). - Carvalho, 2013: 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea ). - Tagliacollo et al., 2016: 28, fig. 5 (phylogeny of Gymnotiformes ). - Crampton et al., 2016: 1-66, table 1, 3-4, figs. 1-7, 11, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus ).

Diagnosis. Brachyhypopomus diazi is diagnosed from congeners by the following combination of characters: bilateral columns at anal-fin terminus 4-5, vs. 3 in all congeners except B. belindae , B. janeiroensis , B. jureiae , B. occidentalis , and B. palenque , and vs. 6 columns in B. bennetti ; pale stripe along middorsal region of body absent, precaudal vertebrae 16-19, vs. 20-26 in B. belindae and B. jureiae ; dorsal rami of the recurrent branch of the anterior lateral line nerve not visible, vs. visible in B. janeiroensis ; continuous or discontinuous dark vertical or diagonally oriented stripes or saddles present on body surface dorsal to lateral line, vs. mottled pattern with no stripes in B. palenque (and preopercular sensory canals incised in preopercle, vs. preopercular sensory canals independent of preopercle in B. palenque ). Brachyhypopomus diazi exhibits similar pigmentation and overlapping counts and morphometric proportions with B. occidentalis . The two species can be distinguished by a more extensive network of depigmented and dark-margin epidermal canals in B. diazi (including in the anterior half of the body) than in B. occidentalis , and by the first branchiostegal ray distinctly narrower than the third branchiostegal ray, vs. the first branchiostegal ray is approximately as wide as the third in B. occidentalis .

Description. Head and body shape, and pigmentation illustrated in Fig. 21 , and in the original description. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 11. Body moderate in depth. Head moderate in length and shallow to broad in depth. Dorsal profile of head slightly convex from occiput to snout, ventral profile of head approximately straight to slightly concave between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with moderate to acute sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 37-57 (median 47, n = 8). Pectoral fin moderate to broad in width, pectoral-fin rays 15-20 (mode of 17 in a population in the río Alpargatón on the Caribbean coast of N Venezuela, and 16 in populations from the río Apure of the Venezuelan Llanos). Precaudal vertebrae 16- 19 (mode of 18 from the río Alpargatón, and 17 from the río Apure), including 2-3 (mode 2) transitional vertebrae. Anal-fin origin slightly (<0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 190-226 (median of 209 from the río Alpargatón and 206 from the río Apure). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Extensive network of prominent depigmented epidermal canals along much of body length; from approximately one head length posterior to nape, to near anal-fin terminus. In anterior half of body canals occur in low density in upper portions of flank, and curve gently in a shallow anterodorsal to posteroventral slope. In second half of body canals occur as multiple parallel wavy lines in two series: one dorsal to lateral line, and another in upper dorsal flank.A lower density of parallel epidermal canals branch from lateral line over body cavity and extend about half a head length ventrally, in an oblique anterodorsal to posteroventral direction. Region below lateral line completely or almost completely free of epidermal canals in posterior half of body (contrasting with many other congeners in which epidermal canals are found parallel to lateral line on both dorsal and ventral side). 4-5 (mode 4) bilateral horizontal columns of electrocytes at anal-fin terminus in immature specimens, mature females, and mature males. 4-6 (mode 5) columns at mid-point between anal-fin terminus and tip of caudal filament in immature specimens and mature females and 5-6 (mode 5) in mature males. Caudal filament short to moderate in length.

Coloration. ( Fig. 21 ). Background tan to dark brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Prominent narrow brown saddles cross much of dorsal surface in anterior third of body. Dorsal region of posterior portion of body is marked with irregular dark patches, which sometimes form an alternating series of blotches either side of dorsal midline. Thin vertical or anteroventral to posterodorsally oriented brown bands extending from dorsal surface. In anterior third of body bands extend across lateral line and across ventral portion of body, often with a misalignment in their continuation across lateral line. In posterior two thirds of body bands usually reach only to lateral line, where they either peter out or fuse to horizontally-oriented dark lines near lateral line. Thin dark lines or vertically elongated dark patches extend from anal-fin margin to dorsal margin of anal-fin pterygiophores in posterior two thirds of body. Wide pale patch with no prominent dark bands or spots extending from about third body length behind head to about one head length anterior to anal-fin terminus in many specimens. Caudal filament darker than body, especially dorsally, ventrally, and near tip; with irregular bands along entire length. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline. Anal-fin rays with uniform light scattering of chromatophores, which fade at distal fin margin, fin rays darker in posterior half. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Size. Moderate adult size, largest specimen examined 193 mm TL, 184 mm LEA (n = 241). Largest male specimen examined 193 mm TL, 184 mm LEA (n = 15). Largest female specimen examined 143 mm TL, 115 mm LEA (n = 15).

Sexual dimorphism. Sexually mature males attain larger sizes than females, and exhibit longer and substantially deeper caudal filaments than immature individuals and breeding females ( Figs. 21 a-b), but do not exhibit an elevated number of bilateral horizontal columns or vertical rows of electrocytes; although the range of electrocyte columns midway from anal-fin terminus to caudal fin filament is sometimes higher in breeding males (5-6, mode 5) than immature specimens and breeding females (4-6, mode 5). Breeding males nonetheless exhibit clearly enlarged electrocytes relative to immature specimens and females. Breeding males with paddle-like lateral compression at caudal filament tip. No known sexual dimorphism in pigmentation.

Geographic distribution. Venezuela ( Fig. 14 ). Brachyhypopomus diazi is known from the northern Orinoco drainage of Venezuela (with most records from the Llanos wetlands), and from coastal drainages of the Caribbean coast of northern Venezuela, from the río Tocuyo drainage to the río Patanemo drainage.

Population variation: We found complete overlap in the range of meristic counts ( Tables 2-5) and morphometric proportions ( Table 11), and observed similar pigmentation, between trans-Andean populations of B. diazi from the río Alpargatón on the Caribbean coast of N Venezuela, and cis-Andean populations from the río Apure of the Venezuelan Llanos. These observations, in combination with molecular data ( Crampton et al., 2016), support the hypothesis that all populations we have assigned to B. diazi are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners, and unique among congeners in exhibiting a trans- and cis-Andean distribution.

Ecological notes. Locally common in high-conductivity rivers (100-400 μScm-1) draining the Andes of the Venezuelan llanos (and their associated floodplains), and from streams and small rivers draining the coastal Andean range of the north Venezuelan Caribbean coast. Brachyhypopomus diazi is typically found in dense marginal emergent aquatic vegetation, or among floating macrophytes (Sullivan & Hopkins, 2009) (WGRC unpublished data). WGRC and NRL recorded the following water parameters at the type locality in the rio Alpargatón drainage, on March 21 2004: conductivity 340 μScm-1, dissolved oxygen 5.2 mgl-1, temperature 27.3°C, and pH 7.1. Here, reproductively mature male and female specimens were captured along with small juveniles (20-40 mm) in marginal grasses and roots. The duration of the breeding season in the río Alpargatón, and the duration and seasonality of breeding in the Llanos populations, and elsewhere, are unknown. Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: In the Orinoco drainage B. diazi co-occurs in geographical sympatry with B. brevirostris , B. bullocki B. beebei , B. regani , and partially with B. sullivani . Of these species, B. diazi only occurs in ecological syntopy with B. brevirostris , B. beebei , and B. regani . Sullivan & Hopkins (2009) note that B. diazi and B. bullocki exhibit habitat partitioning; the former occurring in systems with high conductivity (conductivity> 100 μScm-1), and the latter in system with low conductivity (<15 μScm-1). Brachyhypopomus sullivani is likewise a low-conductivity specialist throughout its geographical range. In Caribbean coastal drainages of Northern Venezuela, B. diazi occurs in the absence of congeners.

Local names. Venezuela: cuchillo.

Remarks. Comments on the type series: The holotype of B. diazi is only known only from the photograph in Fernández- Yépez’s original description. Museum catalog numbers were not provided for the holotype and sole paratype listed in the description, and these specimens have subsequently been lost (pers. comm., F. Provenzano, MBUCV). The collection locality of the lost holotype is given as [“Station 138”] from the “rio Yaracuy ” hydrogeographic complex (a complex which includes the río Salado). Plate 21 of the description includes photographs of “various views of the collecting sites of the species, all west of Puerto Cabello”, one of which features a plaque labeled “139 río Salado”. During a 2004 visit to Carabobo, two of us (WGRC and NRL) located a site where the río Alpargatón (a tributary of the río Salado) crosses the main road leading west from Puerto Cabello and Morón (10°27′N, 68°8′W). The site corresponded clearly to photographs from Plate 21, including a distinctive bridge, and a view towards forested hills. At this site we collected a sizable topotype series (MBUCV-V 35655 and UF 174333).

Material examined. 240 specimens. Venezuela. Apure (localities from río Apure dr., Orinoco dr.). CU 71961, 56, nr. Arichuna , edge of río Apure, 07°42′N, 067°08′W . INHS 32076 , 8 , 96-150 mm, caño Guaritico, 07°33′21″N, 069°38′59″W . MBUCV-V 10809 , 3 , 48-77 mm, 4 km San Juan de Payara on Biruaca-San Juan de Payara rd., caño Payara, affl. río La Piedra, affl. río Arichuna , 07°40′N, 067°34′W . MBUCV-V 11033 , 1, 112 mm, El Negro, San Fernando de Apure, Caramacate, affl. río Negro , ca. 07°50′N, 067°28′W . MBUCV-V 14123 , 1 , female, 110 mm, San Fernando to Apure-Arichuna hwy., ca. 1.5 km past bridge over río Manglar , ca. 07°50′N, 067°28′W . MBUCV-V 19923 , 7 (4 measured: 2 immature 62-63 mm, 1 female, 107 mm, 1 male, 120 mm), Laguna nr. caño Boquerones, nr. Arichuna , affl. río Apure, ca. 07°43′N, 67°17′W . MBUCV-V 20666 , 2 (1 measured, female, 102 mm), río Apure, nr. San Fernando de Apure, 07°53′N, 067°28′W . MCNG 13934 , 2 , caño Las Mercedes, affl. río Apure, 07°53′N, 067°31′W . MCNG 13955 , 1 , hwy. via San Fernando de Apure, no precise locality/ coordinates . MCNG 24161 , 1 , on Boquerones-San Fernando de Apure hwy., no coordinates . UF 176888 , 12 (2 immature, 74-93 mm, 5 female [3CS], 80-106 mm, 5 male, 91-130 mm), Hato El Frio, nr. Mantecal, floodplain lake of río Guaratico , 07°49′32″N , 068′55′23″W. USNM 260254 , 2 , río El Canito, at rd. from San Fernando to Cunaviche , affl. río Cunaviche , 07°28′N , 067′39′W. USNM 260263 , 1, 118 mm, ca. 5 km W San Fernando de Apure, side channel of río Apure, 07°53′N, 067°29′W . Barinas. MBUCV-V 7549 , 1 , 80 mm, quebrada La Yuca, Puente Blanco, ca. 20 km E Barinas, affl. río Masparro, affl. río Apure, Orinoco dr., ca. 08°35′N, 069°59′W . Carabobo. MBUCV-V 13443 , 5 , 47-193 mm (2 sexed, males, 171-193 mm), río Patanemo, E Puerto Cabello, río Patanemo dr., ca. 10°26′N, 067°55′W . MBUCV-V 16986 , 3 (2 measured: 1 female, 136 mm, 1 male, 178 mm), río Urama, río Urama dr., 10°32′N, 068°12′W . MBUCV-V 35655 , 1 (topotype), male, 160 mm , UF 174333 , 16 (topotypes) (7 immature [2CS], 20-132 mm, 4 female [1CS], 100-143 mm, 5 male [1CS], 115-176 mm), mun. Morón, río Alpargatón, at rd. and railway bridge on hwy. 1, 8.4 km Morón , río Salado dr., 10°27′58″N, 068°15′38″W . Cojedes. MBUCV-V 10787 , 1, 135 mm, quebrada El Pozuelo, bridge on San Carlos-Acarigua rd., affl. río Portuguesa, Orinoco dr., ca. 09°35′N, 068°45′W . MCNG 13623 , 1 , caño El Pozuelo, affl. río Portuguesa, affl. río Apure, Orinoco dr., ca. 09°35′N, 068°45′W . MCNG 15605 , 2 , caño Cañafistolo , no coordinates . Guárico (localities from Orinoco dr.). MBUCV-V 14124 , 1 , female, 123 mm, km 273.6, Calabozo-Camaguan hwy., río Apure, no coordinates . MCNG 14404 , 7 , stream E Guayabal, affl. río Orituco , affl. río Guárico, affl. río Apure, 09°09′N, 066°43′W [coordinates for Guayabal ] . MCNG 14483 , 3 , stream between hwy. 2 and Uverito, affl. río Manapire , ca. 09°22′N, 065°54′W [coordinates for Uverito] (listed by Sullivan, 1997). Lara. MBUCV-V 10827 , 1 , female, 69 mm, 60 km W Carora, río Camoruco, río Todistinctive 0°08′N, 070°37′W . MBUCV-V 16985 , 1 , 63 mm, río Los Quediches, headwaters downstream of dam, río Tocuyo dr., ca. 09°57′N, 070°25′W . MCNG 10854 , 1 , stream at km 408, no precise locality/coordinates (listed by Sullivan, 1997) . Monagas. MBUCV-V 10696 , (part) 4, 117-142 mm, Barrancas, Laguna el Guatero, affl. río Orinoco, Orinoco dr., ca. 08°42′N, 062°12′W . Portuguesa (localities from río Apure dr., Orinoco dr.). INHS 61362 , 2 , 104-112 mm, MCNG 15416, 2, MCNG 23675, 2, MCNG 26821, 3, caño Maracá, affl. caño Igues , affl. río Portuguesa, 08°53′11″N, 069°29′18″W (listed by Sullivan, 1997) . MCNG 27290 , 1 , caño Maracá, at bridge on Guanare-Guanarito hwy., affl. caño Igues, affl. río Portuguesa, 08°49′09″N, 069°19′43″W (listed by Sullivan, 1997) . MUSM 13406 , 1 , 58 mm, TNHC 12508, 1, 112 mm, TNHC 12579, 1, 131 mm, TNHC 12663, 3, 95-138 mm, TNHC 12706, 17, 39-141 mm, TNHC, 12774, 2, 149-169 mm, TNHC 12608, 16, 93-135 mm, TNHC 12891, 1, 146 mm, TNHC 12896, 1, 118 mm, TNHC 12938, 4, 68-112 mm, TNHC 13018, 5, 44-124 mm, TNHC 13237, 1, 182 mm, TNHC 13277, 1, 99 mm, TNHC 13313, 3, 129-133 mm, TNHC 13347, 1, 90 mm, TNHC 13367, 4, 110-153 mm, TNHC 15036, 23, 61-174 mm, TNHC 17127, 3, 113-119 mm, 35km SE Guanare, caño (río) Maraca at Urriola Ranch , affl. río Portuguesa, 08°52′30″N, 069°27′40″W . UF 174334 , 2 , 125- 163 mm, río de las Marias, nr. Guanare , affl. río Portuguesa, ca. 09°04′N, 069°39′W .

Figures

Fig. 21. Brachyhypopomus diazi. a. MBUCV-V 35655 (WC04.210304), male from type locality, 160 mm TL (head in lateral view, body in lateral and dorsal view); b. UF 174333 (WC03.210304), female from type locality, 141 mm TL (body in lateral view); Venezuela, río Alpargatón, río Salado dr. Note sexual dimorphism in caudal filament height. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Fig. 14. Collection records for Brachyhypopomus bennetti (circles), B. cunia (squares), and B. diazi (triangles). Holotype locations for B. bennetti and B. cunia, and location of lost holotype for B. diazi are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).