Brachyhypopomus hamiltoni, 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 : 728-731

Brachyhypopomus hamiltoni , new species urn:lsid:zoobank.org:act:F8BA1881-ABCE-4E3C-A39C-09C20739E83E

( Figs. 1g , 28 ; Tables 2-5, 13)

Brachyhypopomus sp. G and sp. H. - Crampton & Albert, 2006: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity).

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

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

Holotype. MCP 45482 , female, 97 mm TL, 80 mm LEA, Brazil, Amazonas , mun. Alvarães , Mamirauá Reserve ( Reserva de Desenvolvimento Sustentável ), Ressaca da Vila Alencar , rio Solimões-Japurá floodplain, Amazonas dr., 03º07′41″S, 064°48′04″W, 8 Mar 2001, W. Crampton & J. Oliveira.

Paratypes. 19 specimens, localities from Amazonas dr., collected by W. Crampton & J. Oliveira unless otherwise stated; localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães ). Brazil. Amazonas. MCP 45250 , 1 ( CS), immature, 80 mm, 26 Nov 1998, MCP 45303 , 1 , immature, 82 mm, 3 Dec 1998, mun. Maraã , Boca do igarapé Juá Grande , lago Amanã , affl. rio Japurá , 02°27′14″S, 064°48′26″W. MCP 45269 , 1 , male, 104 mm, Mamirauá Reserve , Ressaca do Pau , 03º02′03″S, 064º52′13″W, 17 Apr 2001. MCP 45302 , 11 (3 CS, 2 with gills and brain removed), 75-89 mm (9 immature, 64-89 mm, 1 female, 84 mm, 1 male, 93 mm), 2 Dec 1998, MCP 45307 , 1 , female, 93 mm, 16 Feb 1993, mun. Maraã , igarapé Juá Grande , lago Amanã , affl. rio Japurá , 02°28′50″S, 064°48′50″W. MCP 45407 , 1 , immature, 56 mm, mun. Tefé , lago Jacaré, rio Solimões floodplain, 03°11′11″S, 064°43′05″W, 18 Aug 1998. MPEG 27114, 1, 97 mm, lago do Içé, Ilha do Içé , rio Solimões , 6 km NW Tefé, Amazonas dr., 03°16′02″S, 064°40′50″W, 18 May 2012, A. Cardoso & J. Oliveira. MPEG 27115, 2, 78- 78 mm, Mamirauá Reserve , Paraná do Mamirauá, 03º02′58″S, 064°50′57″W, 18 May 2012, A. Cardoso & J. Oliveira .

Non-types. 44 specimens, localities fromAmazonas dr. Brazil. Amazonas (localities listed from the Mamirauá Reserve [ Reserva de Desenvolvimento Sustentável Mamirauá ] are in rio Solimões-Japurá floodplain, mun. Alvarães ). IDSM 460 , 1 , 67 mm, Mamirauá Reserve , cano do lago Sapucaia, 03º04′07″S, 064°48′32″W . MCP 45268 , 1 , immature, 84 mm, MamirauáReserve, ParanáMaiana, 03º06′50″S, 064°47′48″W . MCP 45681 , 5 , immature, 34-56 mm, mun. Tefé, lago Jacaré, rio Solimões floodplain, 03°11′11″S, 064°43′05″W . MPEG 22744 , 2 , 54-66 mm, Mamirauá Reserve , lago Bolsinho, 03º03′47″S, 064°49′59″W . MZUSP 7352 (part), 2, 65-93 mm, mun. Maués, igarapé Limãozinho, affl. rio Maués Açu , ca. 03°24′S, 057°42′W . MZUSP 30058 (part), 1, immature, 60 mm, lago Amanã, affl. rio Japurá , ca. 02°30′S, 064°42′W . MZUSP 55112 , 1 , 65 mm, mun. Santa Isabel do rio Negro, igarapé São João, nr. Santa Isabel do rio Negro (Tapurucuara), affl. rio Negro , ca. 00°24′S, 065°02′W . MZUSP 79663 , 1 , 79 mm, mun. Presidente Figueiredo, rd. branch nr. Marcus Freire, km 13 on AM-240 hwy., affl. rio Preto da Eva , 02°04′06″S, 059°54′33″W . MZUSP 95226 (part), 1, 77 mm, mun. Santa Isabel do rio Negro, Paricatuba, lake, margin of rio Negro , ca. 00°31′S, 065°01′W . Ecuador (localities from río Napo dr.). Napo. MUSM 5693 (part), 1, 120 mm, río Aguarico , R. bank, temporary lake, ca. 00°38′S, 075°21′W [coordinates for mouth of río Aguarico]. Sucumbios. FMNH 102282 , 2 , 72-84 mm, Laguna Zancudococha, affl. río Aguarico , ca. 00°35′S, 075°29′W . FMNH 102285 , 2 , 73-90 mm, affl. to río Cuyabeno, N bank ca. 3 km upstream Laguna Grande de Cuyabeno, affl. río Aguarico , ca. 00°01′S, 076°10′W . FMNH 102291 , 2 , 63-68 mm, N bank affl. to río Aguarico, 2nd affl. downstream from Zancudo, no coordinates. FMNH 121058 , 8 , 21-73 mm, small stream between Laguna Zancudo and Laguna Zancudococha, affl. quebrada Zancudococha, affl. río Aguarico , 00°33′42″S, 075°30′00″W . Peru. Amazonas (localities from río Marañón, affl. río Amazonas ). LACM 41774-1 , 6 , 66-109 mm, Caterpiza , río Santiago , ca. 03°55′S, 077°44′W . LACM 41931-3 , 2 , 82-91 mm, downstream from Caterpiza, río Santiago , ca. 03°55′S, 077°44′W . LACM 42012-4 , 2 , male, 107-125 mm, 1 km downstream from Caterpiza, río Santiago , ca. 03°55′S, 077°44′W . Loreto. MUSM 44704 , 2 , (1 immature, 91 mm, 1 female, 75 mm), stream nr. cocha Capite, nr. Jenaro Herrera, affl. río Ucayali, 04°52′03″S, 073°40′39″W . NRM 27758 , 2 , 59-62 mm, El Estrecho, quebrada de las Granjas, affl. río Putumayo , 02°28′00″S, 072°42′00″W .

Diagnosis. Brachyhypopomus hamiltoni is diagnosed from congeners by the following combination of characters: precaudal vertebrae 19-21, vs. 15-18 in B. batesi , B. benjamini , B. bullocki , B. cunia , B. hendersoni , B. menezesi , B. provenzanoi , B. regani , and B. sullivani , and vs. 24-26 in B. belindae and B. verdii ; pale stripe along middorsal region of body absent, vs. prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament in B. arrayae , B. beebei , B. gauderio , and B. pinnicaudatus ; bilateral columns of electrocytes at the anal-fin terminus 3, vs. 4-6 in B. bennetti , B. diazi and B. occidentalis (except some populations in Colombia and Venezuela, see redescription of B. occidentalis ), and B. palenque ; dark vertical or diagonally oriented stripes or saddles present, vs. absent in B. bombilla , B. draco , and B. jureiae ; anal-fin rays 163-208, vs. 226-293 in B. brevirostris ; absence of conspicuous patches of shiny yellow guanine on the operculum and anterior to pectoral-fin base in live individuals, vs. presence in B. flavipomus ; caudal filament length 18.6-30.0% LEA, vs. 31.3-59.1% in B. janeiroensis ; dark suborbital stripe absent, vs. present in B. walteri . B. hamiltoni can be distinguished from B. alberti by a lower number of pectoral-fin rays, 12-15 (mode, 13), vs. 15- 16 (mode 16) in B. alberti (only 2 of 18 measured specimens of B. hamiltoni exhibited an overlapping number of pectoral-fin rays with B. alberti ). Brachyhypopomus hamiltoni can be further distinguished from B. alberti by the presence of the first of five branchiostegal rays, vs. absence in B. alberti .

Description. Head and body shape, and pigmentation illustrated in Figs. 1g and 28 . Meristic and morphometric data for examined specimens presented in Tables 2-5 and 13. Body moderate in depth.Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head approximately straight to slightly convex from occiput to snout, ventral profile of head approximately straight to slightly concave between operculum and snout, snout triangular to rounded. Eye moderate to large in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 30-39 (median 33, n = 10). Pectoral fin narrow to moderate in width, pectoral-fin rays 12-15 (mode 13). Precaudal vertebrae 19-21 (mode 20), with 1-3 (mode 1) transitional vertebrae. Anal-fin origin slightly (<0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 163-208 (median 180). 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 5). Lateral line continuous. Depigmented epidermal canals present; as an irregular interrupted single groove either side of dorsal midline along most of posterior half body; and as crisscrossing network of grooves parallel to and dorsal to lateral line, reaching about one third of distance from lateral line to dorsal midline, and mostly restricted to posterior third of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at or near a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens, and in populations from both low-conductivity and high-conductivity systems. Caudal filament of moderate length.

Coloration. ( Figs. 1g , 28 ). Background pale tan to dark brown. Dorsal region without prominent depigmented stripe extending along midline from occipital region to base of caudal filament. Dorsal region with irregular dark patches of dark chromatophores which extend into diffuse, narrow, vertical dark bands which extend across lateral line. Some diffuse bands reach ventral midline or anal-fin margin over body cavity. Vertical bands less distinctive in posterior portion of body and mostly do not cross lateral line. Some diffuse vertically-elongated patches of chromatophores extend dorsally from anal-fin margin over anal-fin pterygiophores. Vertical dark bands much less distinct than in most congeners that possess dark vertical or diagonally oriented stripes or saddles on body surface dorsal to lateral line. Series of elongated diffuse horizontal dash-like dark markings present along lateral line in posterior third of body, anterior to anal-fin terminus. Caudal filament darker than body, with irregular dark markings or 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. Anal-fin rays with light scattering of brown chromatophores, usually anal-fin rays darker than pectoral-fin rays. Color in live individuals similar to preserved ones, with opercular region usually rosy due to underlying gills. Individuals from blackwater habitats usually exhibit a darker overall coloration than those in whitewater habitats. Individuals from whitewater habitats often with yellowish tinge to background body color in live individuals.

Size. Small adult size, largest specimen examined 125 mm TL, 100 mm LEA (n = 61). Largest male specimen examined 125 mm TL, 100 mm LEA (n = 4). Largest female specimen examined 97 mm TL, 80 mm LEA (n = 4).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil, Ecuador, and Peru ( Fig. 29 ). Widely distributed in the upper, central, and lower Amazon, and from the middle Negro, but with sporadic collection records.

Ecological notes. In the region of the type locality B. hamiltoni is uncommon. It is known from floating macrophytes in whitewater floodplains at the confluence of rio Solimões and Japurá (see description of B. belindae for water quality parameters in this area), and from the large low-conductivity (usually <30 μScm-1) blackwater floodplain ria lake, lago Amanã; see Crampton (2008) for notes on the water chemistry of lago Amanã. Specimens in reproductive condition were found during the rising and high water period, which is consistent with the reproductive seasonality of sympatric congeners. Stomach contents of specimens from the type locality comprise aquatic insect larvae (primarily Chironomidae ), and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: Brachyhypopomus hamiltoni is known to co-occur in geographical sympatry and ecological syntopy with B. beebei , B. belindae , B. bennetti , B. brevirostris , B. flavipomus , B. hendersoni , B. pinnicaudatus , B. regani , and B. walteri . It also exhibits an allotopic distribution across parts of its range with: B. batesi , B. benjamini ¸ B. sullivani , and B. verdii .

Etymology. The specific name is a patronym (noun in the genitive case) in honor of William D. Hamilton (1936- 2000), British evolutionary biologist, and doctoral advisor of WGRC; for his contributions to Amazonian ecology.

Local names. Brazil: sarapó; Ecuador: cuchillo, yayo; Peru: macana.

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. 28. Brachyhypopomus hamiltoni. MCP 45482 (WC05.080301), holotype, female, 97 mm TL (head in lateral view, body in lateral and dorsal view); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Specimen fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Fig. 29. Collection records for Brachyhypopomus hamiltoni (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).