Brachyhypopomus regani, Crampton & de Santana & Waddell & Lovejoy, 2016

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 : 762-766

Brachyhypopomus regani , new species urn:lsid:zoobank.org:act:F537AD66-390E-4767-926E-0D18

( Figs. 1j , 41 ; Tables 2-5, 17)

Hypopomus brevirostris . -Hopkins & Heiligenberg, 1978: 132, fig. 10, black and white photograph of adult ( Suriname, species and EOD diversity).

Hypopomus artedi . - Hopkins & Westby, 1986: 83, fig. 3, line drawing (Guianas, species and EOD diversity).

Hypopomidae sp. 9. - Crampton, 1996a: 77, table 6.1.a, species list; 79, fig. 6.1 inset 32-33, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2-9.3, table 9.1a,b, hypoxia tolerance; 165-169, table 10.1 reproductive biology ( Brazil, central Amazon, ecology and signal diversity).

Brachyhypopomus electropomus . - Sullivan, 1997: 91 (description in unpublished thesis with disclaimer stating that nomenclatural acts are not available, a nomen nudum, refers also to B. bombilla and B. menezesi ).

Brachyhypopomus sp. 5 . - Crampton, 1998a: 821, table 4, 834, fig. 9, illustration of specimen, with EOD ( Brazil, Amazonas, species and EOD diversity). - Crampton, 1998b: 314, table 2, list of Brachyhypopomus ( Brazil, Amazonas, hypoxia tolerance). - Crampton, 1999: 17 ( Brazil, Amazonas, Mamirauá Reserve, listing of species).

Brachyhypopomus sp. E . - Crampton & Albert, 2006: 672, fig. 23.8, color photograph of head of live individual with EOD, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity).

Brachyhypopomus sp. “reg”. -Crampton, 2011: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. 1 . - Mol, 2012: 598 ( Suriname, catalog of fishes). -Crampton & Ribeiro, 2013: 238, color photograph ( Brazil, rio Madeira, listing of hypopomids).

Brachyhypopomus sp. ‘ele’. - Carvalho, 2013: 177, fig. 37A, color photograph of head showing position of accessory electric organ; 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea ).

Brachyhypopomus sp. “regani ”. - Crampton et al., 2016: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus ).

Holotype. MCP 47022 , female, 128 mm TL, 115 mm LEA, Brazil. Amazonas. Mamirauá Reserve , cano do lago Rato , rio Solimões-Japurá floodplain, Amazonas dr., 03º02′41″S, 064º51′26″W, 14 Mar 2001, W. Crampton & J. Oliveira.

Paratypes. 40 specimens. Brazil. Amazonas (collectedfrom Amazonas dr., by W. Crampton & J. Oliveira; localities from Amazonas dr., localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). BMNH 1998.3.12.183, 1, immature, 117 mm, mun. Tefé, Ressaca do Cachorro , lago Tefé, ( rio Tefé ), 03°19′50″S, 64°46′15″W, 3 Feb 1995 . BMNH 1998.3.12.184-188, 6, immature (1 measured, 90 mm), Mamirauá Reserve , cano do lago Mamirauá, 03º03′51″S, 64º51′05″W, 12 Apr 1994 . BMNH 1998.3.12.189-190, 2 (1 female, 109 mm, 1 male, 134 mm), Mamirauá Reserve , cano do lago Rato, 03º02′41″S, 064º51′26″W, 20 Jan 1995 . INPA 9951 , 8 , 70- 108 mm, Mamirauá Reserve, lago Caetano , 02º50′58″S, 064º55′42″W, Oct 1993 . INPA 18447 , 2 , immature, 66- 79 mm, Mamirauá Reserve, lago Periquito Comprido , 03º04′57″S, 064°46′42″W, Jun 1998 . MCP 45333 , 2 (1 immature, 118 mm, 1, male, 132 mm), Mamirauá Reserve , cano do lago Rato, 03º02′41″S, 064º51′26″W, 2 Apr 1994 . MCP 45334 , 1 , female, 120 mm, Mamirauá Reserve, lago Bolsinha , 03º03′47″S, 064º50′03″W, 5 Apr 1994 . MCP 45335 , 1 , immature, 140 mm, Mamirauá Reserve, cano do lago Mamirauá , 03º03′51″S, 064º51′05″W, 2 Oct 1994 . MCP 45411 , 1 , female, 107 mm, Mamirauá Reserve, cano do lago Sapucaia , 03º04′07″S, 064°48′32″W, 15 Apr 1998 . MCP 45439 , 1 , immature, 107 mm, Mamirauá Reserve, Paraná do Apara , 03º06′40″S, 064°47′52″W, 23 Mar 1995 . MCP 45446 , 4 , 57-109 mm, Mamirauá Reserve, cano do lago Rato , 03º02′41″S, 064º51′26″W , 1997 (no precise date). MCP 45474 , 1, 107 mm, mun. Tefé, Ilha Panamim, rio Solimões floodplain, 03º19′29″S, 064º38′37″W, 31 Jul 2001 . MCP 45475 , 2 , 76-86 mm , MCP 45476 , 1 , female, 141 mm, mun. Tefé, lago Jacaré, rio Solimões floodplain, 03°11′11″S, 064°43′05″W, 18 Aug 2001 . MCP 45484 , 8 (1 not sexed [CS], 105 mm, 2 immature [1CS], 84-90 mm, 2 female, 89-117 mm, 3 male, 104-135 mm [1 with gill and brain removed, 135 mm]), Mamirauá Reserve , cano do lago Mamirauá, 03º06′40″S, 064°47′52″W, 15 Mar 2001 .

Non-types. 189 specimens. Brazil (localities from Amazonas dr.) . Acre. MCP 41043 , 2 , mun. Brasiléia, stream, affl. small river, ca. 2 km hwy. BR-317 on branch 26, affl. rio Purus , 10°56′10″S, 068°56′01″W . Amazonas. (localities from Amazonas dr., localities listed from the Mamirauá Reserve [ Reserva de Desenvolvimento Sustentável Mamirauá ] are in rio Solimões-Japurá floodplain, mun. Alvarães ). IDSM 458 , 1 , 67 mm, MCP 45473 , 3 (1 female, 112 mm, 2 male, 104-119 mm), Mamirauá Reserve , lago Periquito Comprido, 03º04′57″S, 064°46′42″W . INPA 15443 , 1, 143 mm, igarapé Água Viva, nr. Presidente Figueiredo, 12 km on hwy. AM-240, igarapé Mutum, affl. igarapé Urubú, 02°15′13″S, 060°24′59″W . INPA 19945 , 2 , 73-88 mm, Ilha Janauacá, rio Solimões floodplain, ca. 03°43′S, 060°26′W . MCP 41036 (part), 1, 86 mm, mun. Canutama, igarapé São João on hwy. BR-319, ca. 60 km S Humaitá, affl. rio Ipixuna, affl. rio Purus , 07°56′07″S, 063°20′03″W . MCP 45282 , 1 , immature, 80 mm, rio Japurá, at Nova Colômbia, rio Solimões-Japurá floodplain, 02º54′47″S, 064º54′19″W . MCP 45283 , 2 , immature, 73-76 mm, rio Japurá, nr. Boca do lago Mamirauá, rio Solimões-Japurá floodplain, 03º07′03″S, 064º46′51″W . MCP 45284 , 1 , female, 133 mm, Mamirauá Reserve, Ressaca da Vila Alencar , 03º07′41″S, 064°48′04″W . MCP 45285 , 3 (2 female, 100-112 mm, 1 male, 123 mm), Mamirauá Reserve, cano do lago Rato , 03º02′41″S, 064º51′26″W . MCP 45286 , 2 , female, 107-111 mm, Mamirauá Reserve, Ressaca do Pau , 03º02′03″S, 064º52′13″W . MCP 45456 , 2 (1 immature, 103 mm, 1 female, 106 mm), Mamirauá Reserve, cano do lago Rato , 03º02′41″S, 064º51′26″W . MCP 45457 , 3 (1 not sexed [CS], 130 mm, 2 male, 96-134 mm), Mamirauá Reserve, Ressaca da Vila Alencar , 03º07′41″S, 064°48′04″W . MZUSP 23403 , 1 , igarapé Tucuxi, Ati-Paraná, NW Fonte Boa, rio Solimões floodplain, ca. 02°14′S, 066°37′W . USNM 304962 , 1 , 82 mm , Paraná do Marauiá, affl. río Negro , ca. 00°23′S, 065°13′W . Goiás. MZUSP 4887 , 1 , 53 mm LEA, rio Araguaia at Aruanã , affl. rio Tocantins, Amazonas dr., 14°55′S, 051°04′W . Mato Grosso (localities from rio Tocantins dr., Amazonas dr.). MCP 40271 , 5 , mun. Vila Rica, stream on rd. Vila Rica-Confresa rd., affl. Ribeirão Gameleira, affl. rio Araguaia , 10°31′31″S, 051°24′39″W . MCP 40780 , 2 , 66-90 mm, mun. Confresa, Ribeirão Tucunara, hwy. MT-432 between hwy. BR-158 and Terra Indígena Urubu Branco, affl. rio Araguaia , 10°41′25″S, 051°22′52″W . MZUSP 88597 , 2 , 71-80 mm, Cocalinho, ca. 79 km N Cocalinho on hwy. MT-326, Ribeirão Agua Preta, affl. rio Cristalino, affl. rio Araguaia , 14°08′57″S, 051°32′21″W . Pará (localities from Amazonas dr.). MCP 23358 , 3 , 76-88 mm, mun. São Miguel do Guamá, stream on rd. from São Miguel do Guamá to Ourem, ca. 10 km São Miguel do Guamá, affl. rio Guamá , affl . Baía de Marajó, 01°33′18″S, 047°25′41″W . MCP 49412 , 2 , mun. Alenquer, small stream, affl. rio Curuá , 01°36′13″S, 054°55′10″W . MPEG 1127 , 1, 115 mm, mun. Castanhal, Boa Vista do Apeú, rio Apeú, affl. rio Guamá , affl . Baía de Marajó, ca. 01°18′S, 047°59′W . MPEG 2399 , 1 , 97 mm, mun. Castanhal, Boa Vista do Apeú, rio Apeú, affl. rio Guamá , affl . Baía de Marajó, ca. 01°18′S, 047°59′W . MPEG 2402 , 1, 103 mm, mun. Peixe-Boi, rio Peixe-Boi, affl. rio Maracanã, rio Amazonas estuary, 01°11′31″S , 047°18′14′W [coordinates rio Peixe-boi at Peixe-boi]. MPEG 15005 (part), 1, 82 mm, mun. Itaituba, stream at trail head from BR-163, affl. rio Tapajós. , 04°23′41″S, 055°32′20″W . MPEG 24491 , 17 , 84-123 mm, mun. Capanema, igarapé Açaiteuazinho nr. Vila de Tauarí, rio Caeté dr., rio Amazonas estuary, 01°11′45″S, 047°10′51″W . MZUSP 97324 , 1 , 72 mm, mun. Novo Progresso, nr. Mil, rio Jamanxim, affl. rio Tapajós , 07°43′51″S, 055°16′36″W . MZUSP 97544 , 1 , 82 mm, mun. Novo Progresso, affl. rio Jamanxim, bridge on hwy. BR-163, affl. rio Jamanxim, affl. rio Tapajós , 07°21′08″S, 055°17′45″W . USNM 330451 , 1 , 90 mm, Belém , Baía de Marajó, ca. 01°27′S, 048°28′W . Tocantins (localities from rio Tocantins dr., Amazonas dr.). MZUSP 51366 , 2 , 75-76 mm, mun. Araguaçu, Fazenda Praia Alta 2.27 km N Araguaçu, on Araguacu-Barreira do Piqui rd., rio Agua Fria, affl. rio Javaés , affl. rio Araguaia , affl. rio Tocantins, ca. 12°45′S °, 049°55′W . MZUSP 52166 , 3 , 78-90 mm, mun. Araguaçu, Fazenda Praia Alta 2, on Araguaçu-Barreira do Piqui rd., rio Agua Fria, affl. rio Javaés , affl. rio Araguaia , affl. rio Tocantins, ca. 12°43′S, 049°55′W . MZUSP 52214 , 1 , 79 mm, mun. Sandolândia, stream on Sandolândia-Barra do rio Verde rd., ca. 5 km Sandolândia, rio Água Fria, affl. rio Javaés , affl. rio Araguaia , affl. rio Tocantins, ca. 12°32′S, 049°55′W . Ecuador (localities from río Napo dr., Amazonas dr.). Francisco de Orellana. FMNH 102289 , 4 , 27-91 mm, affl. río Payamino, downstream from San José de Payamino, N bank, affl. río Payamino , affl. río Napo, 00°30′S, 077°15′W . QCAZ-I 1828 , 1, 134 mm, QCAZ-I 1829, 1, 132 mm, QCAZ-I 1830, 1, 132 mm, QCAZ-I 1831, 1, 148 mm, QCAZ-I 1832, 1, 136 mm, Parque Nacional Yasuní, km 39 on Pompeya-NPF (oil field) rd., río Tiputini , affl. río Napo, ca. 00°36′S, 076°28′W . Sucumbios. FMNH 102273 , 1 , 53 mm, affl. río Aguarico, N bank, 1-2 km upstream from mouth of río Pushino , affl. río Napo, 00°03′30″N, 076°56′00″W . FMNH 120675 , 1 , 43 mm, small stream between Laguna Zancudo and Laguna Zancudococha, affl. quebrada Zancudococha, affl. río Aguarico , affl. río Napo, ca. 00°26′S, 076°36′W . KU 13802, 1, 127 mm, río Conejo at Santa Cecília, affl. río Aguarico , affl. río Napo, ca. 00°06′N, 076°51′W . Guyana. Upper Takutu-Upper Essequibo (localities from Takutu River dr., affl. rio Branco, affl. rio Negro, Amazonas dr.). ANSP 179507 , 1 , 81 mm, 31.2 km NW Sand Creek village, Sauriwau River , 03°06′52″N, 059°46′32″W . AUM 48079 , 1 , 82 mm, creek, 2nd bridge from Moco-Moco power station to Lethem , 03°18′10″N, 059°39′01″W . CU 71937, 11, Moco-Moco Creek , 15 km W Lethem. ca. 03°15′N, 059°39′W (listed by Sullivan, 1997) . CU 71939, 3, CU 71940, 1, CU 71941, 2, USNM 209197 , 1 , 89 mm LEA, overflow of Moco-Moco Creek nr. Moco-Moco village, Kumaka Swamp , ca. 15 km E Lethem, ca. 03°19′N, 059°40′W (listed by Sullivan, 1997) . USNM 209196 , 1, 135 mm, USNM 209198 , 1, 105 mm, Rupununi, Moco-Moco Creek , ca. 03°15′N, 059°39′W . USNM 209200 , 1, 110 mm, Rupununi, creek in swampy area, nr. Moco-Moco Creek , ca. 03°15′N, 059°39′W . Peru. Amazonas. LACM 41930-5 , 1, 129 mm, LACM 41934-4, 2, 116-146 mm, LACM 41935-2, 1, 127 mm, LACM 41936-5, 1, 138 mm, 500 m upstream from Caterpiza, río Santiago , affl. río Marañón , affl. rio Amazonas , Amazonas dr., ca. 03°55′S, 077°44′W . Loreto (localities from Amazonas dr.). AMNH 78112 , 1 , 77 mm, río Tahuayo , ca. 04°03′S , 073°08″W. AMNH 78114 , 1, 140 mm, río Yarapá , affl . río Ucayali, ca. 04°31′S, 073°22′W . INHS 43308 , 2 , 84-87 mm, Maynas, 11 km SSW Iquitos, río Itaya , 03°49′48″S, 073°18′03″W . INHS 52032 , 1, 125 mm, Ullpa, caño Moena, nr. confl. with caño Ullpa, SE Iquitos, affl. río Itaya , 03°46′20″S, 073°14′17″W . INHS 54796 , 1 , 70 mm, floodplain of río Marañón , S Nauta, 04°30′36″S, 073°34′06″W . MUSM 4341 , 1, 118 mm, MUSM 17308 , 2 , 91-93 mm, Yurimáguas, San Ramón, quebrada Simay, affl. río Huallaga, affl. río Marañón , ca. 05°56′S, 076°06′W . MUSM 14494 (part), 2 (1 immature, 104, 1 male, 156 mm), Maynas, Lagartococha, Aguas Negras , río Aguarico , affl. río Napo , 00°31′38″S, 075°15′41″W . MUSM 14497 (part), 6, 91-138 mm, Puesto de Vigiliancia area MH93LO, río Napo , 00°58′S, 075°11′W . MUSM 14498 (part), 1, 124 mm, mun. Maynas, Puesto de Vigilancia Arcadia, río Napo , 00°59′37″S, 075°18′30″W . MUSM 18538 , 1 , 71 mm, nr. Musha Carusha, río Pastaza, affl. río Marañón , 04°26′54″S, 076°39′28″W . MUSM 21896 , 1 (not measured), MUSM 21983 , 2 , mun. Nauta, Reserva Nacional ( RN) Pacaya Samiria, quebrada Llanchama, affl. río Yanayacu-Pucate , río Marañón , ca. 04°39′S, 073°50′W . MUSM 23141 , 1 , Alto Amazonas, Abanico del Pastaza, stream affl. río Platanoyacu, río Corrientes , río Tigre , río Marañón , ca. 03°07′S, 075°40′W . UF 126192 , 1, 125 mm, RN Pacaya Samiria, río Pacaya , affl . río Ucayali, ca. 05°16′S, 074°27′W . UF 129816 , 1 , 62 mm, UF 131404 , 1 , immature, 100 mm, RN Pacaya Samiria, caño Yarina, río Pacaya , affl . río Ucayali, 05°25′56″S, 074°30′01″W . UF 131405 , 1 , immature, 94 mm, RN Pacaya Samiria, cocha Yarina, río Pacaya , affl . río Ucayali, 05°23′58″S, 074°32′05″W . Suriname. Brokopondo. UF 177362 , 7 (5 female, 119-132 mm, 2 male, 133-141 mm), Affobaka rd. from Paranam bauxite refinery to Brokopondo Reservoir, bridge over Marshall kreek, Suriname River dr., 05°14′40″N, 055º 06′05″W . Marowijne. UF 177360 , 12 (7 female, 105-114 mm, 5 male, 98-129 mm), small stream on rd. from Paramaribo to French Guiana, affl. Cottica River , Commewijne River dr., 05°34′51″N, 054°15′31″W . UF 177363 , 2 , female, 105-109 mm, small stream on rd. from Paramaribo to French Guiana, affl. Cottica River , Commewijne River dr., 05°35′11″N, 054°17′05″W . Venezuela (localities from Orinoco dr.). Anzoátegui. MHNLS 9360 , 1 , 83 mm LEA, río Morichal Largo, río Orinoco delta, ca. 09°26′N, 062°24′W (listed by Sullivan, 1997) . Apure. INHS 28179 , 4 , 90-102 mm, 58 km SSW Bruzual , caño Guaritico, affl. río Apure, 07°33′09″N, 069°38′40″W . INHS 28360 , 7 , 72-91 mm, 62 km E Elorza on hwy. to La Victoria at Charal, río Orichuma , affl. río Apure, ca. 07°04′N, 070°01′W . INHS 30112 , 1 , 84 mm, 58 km SSW Bruzual , caño Guaritico, affl. río Apure, 07°33.24′N, 069°38.68′W . MCNG 11032 (part), 5, 79-98 mm LEA, caño Maporal, río Caicara , affl. río Apure, ca. 07°24′N, 069°32′W (listed by Sullivan, 1997) . Barinas. MCNG 5611 , 1 , Reserva de Ticoporo, affl. río Suripa , affl. río Apure, ca. 08°09′N, 070°50′W (listed by Sullivan, 1997) . Bolivar. AUM 22303 , 1, 106 mm, río Chaviripa, on Caicara-Puerto Ayacucho rd. , 07°07′57″N, 066°29′56″W . FMNH 109967 , 1 , 38 mm, caño Wani, affl. río Caura , 06°04′47″N, 064°55′20″W . MCNG 19941 , 1 , MCNG 19999, 1, stream affl., río Caura, no coordinates. MHNLS 8783 , 1 , 83 mm LEA, Raudales del Cambur [El Raudal, caño Cambur], 20 km [SE] bridge at Maripá , ca. 07°22′N, 065°18′W (listed by Sullivan, 1997) . Monagas. MBUCV 14122 , 1 , 97 mm LEA, bridge over caño Piedritas on Temblador-Barrancas hwy., affl. río Urucoa, río Orinoco delta, ca. 08°49′N, 062°29′W (listed by Sullivan, 1997) . MHNLS 6512 , 1 , 76 mm LEA, inundated area, Chaguaramas, río Urucoa , ca. 08°40′N, 062°45′W (listed by Sullivan, 1997) . Portuguesa. TNHC 12703 , 2 , 64-83 mm, 35 km SE Guanare , caño (río) Maraca at Urriola Ranch, affl. río Portuguesa, affl. río Apure, 08°52′30″N, 069°27′40″W . Tachira. INHS 35527 , 1 , 92 mm, [stream] just W junction between hwy. 5 and hwy. 19, río Caparo, affl. río Anaro , affl. río Apure, 07°32′01″N, 071°34′56″W .

Diagnosis. Brachyhypopomus regani is diagnosed from congeners by the following combination of characters:

accessory electric organ over opercular region present, vs. absent in all congeners except B. bombilla , and B. menezesi ; dorsal surface with large dark blotches against a lighter background, vs. dorsal surface speckled with small brown chromatophores on a pale background in B. bombilla ; caudal filament length 11.1-17.9%, vs. 24.-33.3% LEA in B. menezesi .

Description. Head and body shape, and pigmentation illustrated in Figs. 1j and 41 . Meristic and morphometric data for examined specimens presented in Tables 2-5 and 17. Body moderate to broad in depth. Head moderate to long in length and shallow to moderate in depth. Dorsal profile of head approximately straight to slightly concave from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. Accessory electric organ (AEO) over operculum present and very prominent; skin over AEO completely depigmented; border rounded and very conspicuous. Gill filaments on first gill arch 35-45 (median 40, n = 9). Pectoral fin narrow to moderate, pectoral-fin rays 14-16 (no mode, median 15). Precaudal vertebrae 16-18 (mode 17), with 1-2 (mode 2) transitional vertebrae. Anal-fin origin slightly (<0.25 HL distance) anterior to tip of pectoral fin. Anal-fin rays 165-205 (median 184). 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. Multiple groove-like depigmented epidermal canals, some with dark borders, form parallel striations mostly dorsal to lateral line in posterior portion of body, beginning ca. two thirds of LEA; striations reaching 1-4 scales (including lateral line series) dorsally, and occasionally (with much lower density) 1-2 scales ventrally. Epidermal canals absent in anterior portion of body; never form a pair of long irregular lines either side of dorsal surface in dorsal portion of flank; do not form isolated horizontal wavy line midway from lateral line to dorsal midline in midbody or anterior portion of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Electrocytes of hypaxial electric organ extend anterior to anal and urogenital pores and appear to extend into opercular area to form paired accessory electric organ. Caudal filament short.

Coloration. ( Figs. 1j , 41 ). Background light tan to brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Dorsal region mottled with irregular, indistinct dark blotches against a homogenous lighter background (contrasting to a speckling with small brown chromatophores in B. bombilla and to much more distinct dark blotches in B. menezesi ). Dark mottling restricted to dorsal region, extending to around mid-distance from dorsal midline to lateral line. No vertical stripes or lines on flank, some vague irregular dark markings over anal-fin pterygiophores, flank otherwise relatively free of markings. Caudal filament darker than body, with some irregular dark markings. Head with evenly scattered dark chromatophores, darker dorsally. Eye with indistinct to very distinct suborbital patch or stripe of chromatophores and subcutaneous pigmentation. Region over AEO completely depigmented. Border of AEO often with very dark chromatophores. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline in distal third to half, with scattered or fused light brown chromatophores on proximal half. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Size. Small adult size, largest specimen examined 156 mm TL, 130 mm LEA (n = 230). Largest male specimen examined 156 mm TL, 130 mm LEA (n = 17). Largest female specimen examined 141 mm TL, 125 mm LEA (n = 28).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil, Ecuador, Guyana, Peru, Suriname, and Venezuela ( Fig. 42 ). Widely distributed through the Amazon basin, including multiple sites in the upper Amazon, the Negro, Purus, Tapajós, and Araguaia drainages. Absent from the upper Madeira, above its major falls beginning at Porto Velho, where the closely related species B. bombilla occurs. Known also from northern portions of the Orinoco drainage, the Essequibo River, and some coastal drainages of Guyana.

Ecological notes. In the central and upper Amazon B. regani is restricted to high-conductivity whitewater floodplains – occurring in floating rafts of macrophytes, and the leaf litter of newly-inundated forest ( Crampton, 1996a; 1998a). Breeding occurs in floating macrophytes during the rising and high water period ( Crampton, 1996a, 165). Like other congeners in this habitat, B. regani is able tolerate protracted seasonal hypoxia. However, in experimental conditions it is less tolerant of anoxia than syntopic congeners ( Crampton, 1998b). Unlike most congeners B. regani does not undertake aerial gill respiration during experimentally-induced hypoxia. Instead it wedges itself into roots near the water surface and exhibits a variant of aquatic surface respiration in which water at the surface meniscus is passed across its gills by buccal pumping ( Crampton, 1998b). Populations assigned here to B. regani from the lower Amazon in the vicinity of Belém, coastal Suriname, and in the rio Negro (and possibly also the rio Tapajós and rio Araguaia) have a noticeably different ecology, occurring in constantly normoxic rainforest streams and small rivers with relatively low conductivity (10-30 μScm-1) (WGRC unpublished data). We suspect that future studies of ecological, genetic, and EOD variation in this widely distributed species may reveal additional cryptic species. Specimens from whitewater floodplain systems of the central Amazon ( Crampton, 1996a: 136), and also terra firme stream from coastal Suriname (WGRC unpublished data), exhibit similar stomach contents, comprising aquatic insect larvae, microcrustacea, and other small aquatic invertebrates with a predominance of Chironomidae larvae.

Co-occurring congeners: In the upper, central, and lower Amazon (excluding the upper Madeira), B. regani occurs in sympatry and ecological syntopy with B. arrayae (in lower Madeira), B. beebei , B. belindae , B. bennetti , B. brevirostris , B. flavipomus , B. hamiltoni , B. pinnicaudatus , and B. walteri , and exhibits an allotopic distribution with B. alberti (in lower Madeira), B. batesi , B. benjamini , B. cunia (in lower Madeira), B. hendersoni , B. sullivani , and B. verdii . In the rio Negro B. regani occurs in sympatry (and probably in syntopy) with B. batesi , B. beebei , B. brevirostris , B. bullocki ¸ B. hamiltoni , B. hendersoni ¸ B. sullivani , and B. walteri . In the río Orinoco basin B. regani occurs in sympatry with B. beebei , B. brevirostris , B. bullocki , B. diazi , and B. sullivani . In the Essequibo River B. regani occurs in sympatry with B. beebei , B. brevirostris , B. bullocki ¸ B. hendersoni ¸ B. sullivani , and B. walteri . In Coastal Suriname and French Guiana B. regani occurs in sympatry with B. beebei , B. brevirostris , and B. pinnicaudatus .

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Charles Tate Regan (1878-1943), British ichthyologist, for his contributions to Neotropical ichthyology.

Local names. Brazil: sarapó; Ecuador: cuchillo, yayo; French Guiana: poisson couteau (French) (and multiple creole/Amerindian names), Guyana: knife fish; Peru: macana; Suriname: saprapi; Venezuela: cuchillo.

Figures

Fig. 1. Live individuals of 12 sympatric species of Brachyhypopomus and one species of Microsternarchus from the vicinity of Tefé, Amazonas, Brazil (Amazonas dr.). a. Brachyhypopomus batesi MCP 45312 (WC01.191293b), immature, 102 mm TL. b. Brachyhypopomus beebei head – uncat., immature, 75 mm TL; body – MCP 45450 (WC04.090600), female, 178 mm TL. c. Brachyhypopomus belindae MCP 45430, paratype, immature, 104 mm TL (photographed out of water, close up of head not available). d. Brachyhypopomus bennetti MCP 45451, male, 196 mm TL. e. Brachyhypopomus brevirostris uncat., immature, 224 mm TL. f. Brachyhypopomus flavipomus MCP 45453 (WC09.090600), female, 98 mm TL. g. Brachyhypopomus hamiltoni MCP 45482 (WC05.080301), holotype, female, 97 mm TL. h. Brachyhypopomus hendersoni MCP 45489, female, 164 mm TL. i. Brachyhypopomus pinnicaudatus MCP 45455, female, 135 mm TL. j. Brachyhypopomus regani, MCP 45285 (WC02.100301), male, 119 mm TL. k. Brachyhypopomus sullivani MCP 45464 (WC04.210201), immature, 79 mm TL. l. Brachyhypopomus walteri MCP 45458 (WC 03.090600), male, 161 mm TL. m. Microsternarchus bilineatus uncat., 85 mm TL.

Fig. 41. Brachyhypopomus regani. MCP 47022 (WC04.140301), holotype, female, 128 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Note prominent opercular accessory electric organ (pale structure). Scale bars = 5 mm.

Fig. 42. Collection records for Brachyhypopomus regani (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).