Amblystilbe howesi, Fowler, 1940

Bertaco, Vinicius A., Chuctaya, Junior, Jerep, Fernando C. & Malabarba, Luiz R., 2023, Revision of Prodontocharax and revalidation of Amblystilbe (Teleostei: Characidae: Cheirodontinae), with description of a new species, Neotropical Ichthyology (e 230031) 21 (3), pp. 1-32 : 20-25

Amblystilbe howesi, Fowler, 1940

( Figs. 11–13 ; Tab. 2)

Amblystilbe howesi Fowler, 1940:85 , fig. 47 (type-locality: Boca Chapare, Río Chimore, Cochabamba, Amazon system, Bolivia).

Prodontocharax alleni Böhlke, 1953:661 (type-locality: Cashiboya, Peru, Río Ucayali). —Ortega, Vari, 1986:09 (catalog). —Vari, Howe, 1991:35 (catalog). —Malabarba, 2003:218 (listed). —Barriga Salazar, 2014:109 (listed to Ecuador). —Sarmiento et al., 2014:185 (listed to Bolivia). —Meza-Vargas et al., 2021:19 (listed to Loreto, Peru). —Chuctaya et al., 2022:24 (listed to Ucayali basin, Peru).

Prodontocharax howesi . —Malabarba, 2003:218 (valid species). —Sarmiento et al., 2014:185 (listed to Bolivia).

Diagnosis. The same for the genus.

Description. Morphometric data summarized in Tab. 2. Largest specimen 44.4 mm SL. Body elongate and compressed, with greatest body depth at or slightly anterior to dorsal-fin origin. Dorsal body profile convex from nostril to dorsal-fin origin, slightly convex at supraoccipital; nearly straight or slightly concave from first dorsal-fin ray to caudal peduncle. Ventral head profile nearly straight. Ventral body profile convex from pectoral-fin origin to pelvic-fin origin, and straight to anal-fin origin. Anal-fin base straight. Caudal peduncle elongate, slightly concave in the dorsal and ventral margins.

Head relatively small. Snout pronounced, nearly pointed anteriorly. Mouth distinctly ventral, mouth slit at horizontal through inferior border of eye. Maxilla very short. Obliquely positioned maxilla ending at vertical near or at anterior border of eye and at horizontal on inferior eye border. Premaxilla with 8 or 10 tricuspid teeth, central cusp slightly longer and broader than lateral cusps; distal margin of teeth arched (n = 28). Maxilla with 4 to 5 tricuspid teeth, rarely conical (n = 28). Dentary with 11 to 13 teeth; anterior 10 large teeth, tricuspid, followed posteriorly by 1 to 3 small, conical teeth (n = 28). Anterior 7 to 8 dentary teeth inserted at anterior border of bone and anteriorly projected (n = 28); dentary teeth main axis positioned horizontally. All cusps tips slightly curved inside the mouth ( Fig. 12 ).

Dorsal-fin rays ii,9* (n = 114); first unbranched ray approximately half length of second ray. Dorsal-fin origin slightly behind to vertical line projected through pelvic-fin origin. Adipose fin located approximately in vertical through fourth and fifth last anal-fin rays insertion, counted from posteriormost branched ray. Anal-fin rays ii– iv,19–25 (iii,24*, mean = 22.4, n = 134). First unbranched ray normally only apparent in cleared and stained specimens. Anal-fin profile smoothly concave. Branched anal-fin ray decreasing rapidly from first to fifth or sixth rays and gradually decreasing in remaining rays. Anal-fin origin posteriormost to vertical line projected through base of last dorsal-fin rays. Pectoral-fin rays i,11–13 (i,12*, mean = 11.7, n = 113). Pectoral fin not reaching pelvic-fin origin in both sexes. Pelvic-fin rays i,7* (rarely i,8; n = 115). Pelvic-fin origin anterior to a vertical line projected through dorsal-fin origin. Caudal fin forked, with 19* principal rays (n = 112); lobes similar in size. Dorsal procurrent rays 9–12, and ventral procurrent rays 9 (n = 6).

Scales cycloid, moderately large. Lateral line complete. Scales in longitudinal series 35–39 (37*, mean = 36.3, n = 101). Scale rows between dorsal-fin origin and lateral line 6*–7 (mean = 6.0, n = 109); scale rows between lateral line and pelvic-fin origin 4*–5 (mean = 4, n = 109). Predorsal scales 9–13 arranged in regular series (10*, mean = 10.5, n = 88). Scales rows around caudal peduncle 14* (n = 111). No modified scales on caudal-fin. Scale sheath along anal-fin base formed of 4–11 scales in single series, extending to base of fifth to tenth branched rays.

Precaudal vertebrae 17–18; caudal vertebrae 18–20; total vertebrae 35–37. Supraneurals 4–5 (n = 11). Gill-rakers of first gill arch 11–14 on upper limb and 19–20 (n = 6) on lower limb.

Coloration in alcohol. General ground body color brownish or pale yellow. Dark dorsum pigmentation from head to caudal peduncle. Dark unpigmented triangular area at pseudotympanum. Scales of body without dark chromatophores. Broad and conspicuous silvery midlateral body stripe extending from head to caudal peduncle. All fins without pigments. Some specimens that have lost some guanine pigments appear to have midlateral dark stripe ( Fig. 11 ).

Coloration in life. Overall body and head color pattern yellowish and silver. Upper portion of the eye is slightly yellowish. Dorsal, pelvic and anal fins yellowish, caudal fin reddish and pectoral fin hyaline ( Figs. 13A, B ). A specimen photographed in life, and/ or recently fixed, presents the dorsal, pectoral, pelvic, and anal fins yellowish and the caudal fin reddish (Lima et al., 2013:340).

Sexual dimorphism. In mature specimens, males differ from females by the presence of bony hooks on the anal and pelvic-fin rays. The anal-fin hooks are located along the posterior margin of the last unbranched ray, and the first to seventh branched ray (MUSM 259, 2294, and 40534). Little knobs were found on the first unbranched ray of the anal fin resembling initial stages of development of bony hook in a single male specimen (MZUSP 12406). The pelvic-fin hooks are located along the posterior margin of the first and seventh branched ray. Additionally, sexual dimorphism is observed in relation to the number of lamellae in the olfactory lobe (MUSM 40534), with 44 lamellae in total in males and 30 lamellae in total in females.

Geographical distribution. Amblystilbe howesi is known from Amazonas River basin, Bolivia, Brazil and Peru ( Fig. 4 ).

Ecological notes. Based on field information from material cataloged in the fish collections of the MCP, MUSM, and UFRGS. All specimens of A. howesi were collected on shallow beaches near the riverbanks (up to 1.5 m deep), in dark and moderately flowing water, sandy bottom and a small amount of aquatic and riparian vegetation ( Fig. 14 ). Some specimens (MCP 39868) also were captured in a nocturnal collection using a beach seine net in the rio Mamoré.

Conservation status. No significant threats were identified for the Amblystilbe howesi , which is suggested to be categorized as Least Concern (LC), according to IUCN criteria (IUCN, 2022).

Material examined. Amblystilbe howesi : Bolivia, Cochabamba. ANSP 69070, 41.8 mm SL, holotype of Amblystilbe howesi, Boca Chapare , Río Chimore, 28 Aug 1937, M. A. Carriker & G. Howes. ANSP 69071, 10 of 20, 38.5–41.7 mm SL, paratypes of Amblystilbe howesi , collected with the holotype. Prodontocharax alleni : Peru, Ucayali. CAS 117472, 33.6 mm SL, holotype of Prodontocharax alleni lake of Río Ucayali, Cashiboya, ca. 07º31’S 74º55’W, 3–4 Aug 1920, W. R. Allen. CAS 117473, 16 (1 c&s), 28.3–37.1 mm SL, CAS 119050, 8, 24.7–31.0 mm SL, USNM 157366, 1, 35.6 mm SL, paratypes of Prodontocharax alleni , collected with the holotype. Bolivia, Santa Cruz. AMNH 77544, 1, 39.2 mm SL, rio Mamoré, about 2 km N of mouth of Río Chapare, 31 Jul 1965, M. P. Maclean. Brazil, Amazonas. MCP 14928, 15 (3 c&s), 26.7–43.5 mm SL, rio Solimões, across Jacaré, near Fonte Boa, 7 Oct 1968, EPA (Expedição Permanente da Amazônia). MCP 17088, 2 c&s, 40.0– 41.6 mm SL, rio Solimões, Fonte Boa, 6 Oct 1968, EPA. MCP 31917, 1, 44.2 mm SL, rio Solimões, ilha do Içé, Alvarães, 03º16’36”S 64º41’01”W, 1 Jan 2001, W. Crampton. MZUSP 12405, 15, 26.1–35.1 mm SL, rio Solimões, ilha Sorubim, Coari, 04º05’38”S 63º08’39”W, 29 Nov 1968, EPA. MZUSP 12406, 5, 33.2–38.0 mm SL, rio Japurá, Manacabi, 02º45’07”S 64º51’54”W, 30 Oct 1968, EPA. MZUSP 12407, 42 (6 c&s), 38.1–44.4 mm SL, rio Solimões, Fonte Boa, 02º30’09”S 66º05’47”W, 6 Oct 1968, EPA. UFRGS 12877, 1, 26.3 mm SL, UFRGS 21754, 1, 30.9 mm SL, rio Juruá near Furo do Pupunha, Carauari, 05º06’44”S 67º10’26”W, 14 Jun 2008, L. R. Malabarba, V. A. Bertaco, F. C. Jerep, T. P. Carvalho & C. M. Bührnheim. UFRGS 21765, 3, 24.7– 28.7 mm SL, rio Juruá, 2 km above mouth of Juburi, Carauari, 05º10’15”S 67º13’27”W, 15 Jun 2008, L. R. Malabarba, V. A. Bertaco, F. C. Jerep, T. P. Carvalho & C. M. Bührnheim. UFRGS 21803, 2, 21.1–21.4 mm SL, sand beach of rio Juruá, Carauari, 05º06’20”S 67º02’33”W, 17 Jun 2008, L. R. Malabarba, V. A. Bertaco, F. C. Jerep, T. P. Carvalho & C. M. Bührnheim. USNM 356381, 17 of 19, 29.1–42.0 mm SL, rio Amazonas, Manaus, ca. 03º14’S 59º59’W, 8 Nov 1977, P. Bayley. Rondônia. MCP 39868, 50 (2 c&s), 22.8–40.6 mm SL, rio Mamoré at Cristo Rei district, rio Madeira basin, Guajará-Mirim, 10º47’03”S 65º20’58”W, 25 Jul 2004, R. E. Reis, P. A. Buckup, P. Lehmann, V. A. Bertaco & F. Langeani. UFRGS 23293, 2, 40.3–44.9 mm SL, mouth of rio Jaci-Paraná into rio Madeira, Porto Velho, 09º09’41”S 64º23’55”W, 30 Nov 2014, M. Granai, L. F. M. Neto & R. R. Luna. UFRGS 25775, 22, 22.5–35.8 mm SL, rio Madeira, UHE Jirau, Porto Velho, 08º49’32”S 63º58’43”W, 1 Jul 2016, M. Granai, L. F. M. Neto & R. R. Luna. UFRGS 26693, 1, 30.4 mm SL, UHE Santo Antônio, above Cachoeira de Morrinhos, São Carlos, 09º00’46”S 64º15’05”W, 28 Jun 2015, M. Granai, L. F. M. Neto & R. R. Luna. Peru, Loreto. ANSP 149926, 12, 36.0– 41.9 mm SL, Río Amazonas (Maranon) Isla Iquitos, 03º31’56”S 73º04’28”W, 16 Oct 1955, M. Hohn. INHS 39883, 14, 24.1–39.8 mm SL, Río Amazonas across from Puebla Gallito, 7.68 mi SE Iquitos, 03º49’15”S 73º09’43”W, 21 Aug 1996, M. H. Sabaj et al. INHS 40242, 2, 31.2–35.7 mm SL, Río Amazonas, about 10 and 40 min upstream from mouth caño Zapatilla, near town of Yanashi, ca. 03º32’S 72º17’W, 14 Aug 1996, M. H. Sabaj et al. MUSM 258, 11, 37.5– 38.7 mm SL, Río Amazonas, Brinet., 04º01’04”S 71º05’43”W, 27 Sep 1982, H. Ortega. MUSM 10769, 3, 33.5–40.3 mm SL, Amazonas, Santa Elena, 02º10’43”S 73º50’26”W, 25 Sep 1973, W. Medina. MUSM 18088, 1, 42.6 mm SL, Parinari, Río Marañón, Frente a Berlin, 04º33’45”S 74º28’25”W, 8 Mar 2001, H. Ortega. MUSM 18103, 1, 48.2 mm SL, Nauta, Río Marañón, Gran Punta, 04º30’30”S 73º33’47”W, 10 Mar 2001, H. Ortega. MUSM 40534, 104, 28.2–48.8 mm SL, Parinari, Río Marañón, Santa Rita de Castilla, 04º38’20”S 74º20’16.9”W, 30 May 2011, J. Chuctaya. MUSM 40676, 57, 16.1–46.7 mm SL, Río Marañón, Trompeteros, 04º45’14”S 75º04’27”W, 29 May 2011, M. Rojas. MUSM 42219, 9, 38.2–42.7 mm SL, Río Marañón, aguas arriba de la CCNN San Pedro, 04º44’53”S 74º52’27”W, 15 Nov 2011, J. Chuctaya. MUSM 42243, 9, 37.9–41.8 mm SL, Trompeteros, Río Marañon, 04º45’02”S 74º51’10”W, 14 Nov 2011, J. Chuctaya. MUSM 48489, 11, 39.7–42.7 mm SL, Urarinas, Río Marañón, San Pedro, 04º45’03”S 75º04’18”W, 25 Nov 2013, D. Faustino. MUSM 50027, 1, 32.1 mm SL, Urarinas, Río Marañón, San Pedro, 04º45’03”S 75º04’18”W, 25 Jun 2014, D. Faustino. USNM 280635, 1, 19.7 mm SL, Río Amazonas about 30 km downriver of Iquitos, 03º31’56”S 73º04’28”W, 21 Aug 1986, R. P. Vari, H. Ortega & A. G. Gerberich. San Martín. MUSM 67360, 1, 30.6 mm SL, Mariscal Caceres, Pajarillo, Amazonas, Río Huallaga, 07º10’55”S 76º41’46”W, 23 Jun 2019, R. Quispe. Ucayali. MUSM 257, 4, 21.41–32.07 mm SL, Pucallpa, Río Ucayali, Bahuanisho, 08º32’26”S 74º20’20”W, 20 Apr 1983, H. Ortega. MUSM 259, 22, 37.6–40.6 mm SL, Ucayali, Pucallpa, Río Ucayali, Bagazan, 04º43’21”S 73º31’55”W, H. Ortega. MUSM 582, 15, 24.3–40.6 mm SL, Masisea, Río Ucayali, 08º33’03”S 74º20’03”W, 6 Oct 1975, H. Ortega. MUSM 1875, 64, 17.5–28.1 mm SL, Pucallpa, Río Ucayali, Bahuanisho, 08º32’26”S 74º20’20”W, 21 May 1974, H. Ortega. MUSM 2102, 1, 41.1 mm SL, Pucallpa, Bagazan, 04º43’21”S 73º31’55”W, 22 Dec 1986, H. Ortega. MUSM 2294, 5, 41.4–44.8 mm SL, Ucayali, Pucallpa, Río Ucayali, 08º19’51”S 74º35’30”W, 22 Dec 1986, H. Ortega-A. MUSM 3143, 3, 42.3– 44.6 mm SL, Requena, Genaro Herrera, Ucayali, 04º54’44”S 73º40’59”W, 28 Feb 1992, P. de Rham & F. Chang. MUSM 9800, 2, 39.9–42.3 mm SL, Pucallpa, Río Ucayali, 08º19’51”S 74º35’30”W, 30 Oct 1982, C. Villanueva. MUSM 15053, 3, 34.0– 37.5 mm SL, Coronel Portillo, Pucallpa, Ucayali, Pto La Hoyada, 08º21’45”S 74º31’10”W, 20 Aug 1984, H. Ortega. MZUSP 25943, 1, 38.3 mm SL, Río Ucayali, Masisea, 08º36’28”S 74º18’19”W, 6 Nov 1975, H. Ortega. MZUSP 26149, 1, 39.0 mm SL, Río Ucayali, Bagazan, Cel. Portillo, 08º23’17”S 74º34’50”W, 25 Nov 1979, H. Ortega. UFRGS 27444, 9, 40.4–44.8 mm SL, Playa San José, Río Ucayali, near Contamana, 07°13’58”S 74°34’48”W, Sep 2018, J. Chuctaya. UFRGS 27445, 3, 40.5–43.1 mm SL, Río Ucayali at Capironal, near Contamana, 07°19’19”S 75°12’44”W, Sep 2018, J. Chuctaya. UFRGS 27446, 4, 32.8–42.3 mm SL, Río Ucayali at Cushibatay, near mouth of Río Cushibatay, 07°05’14”S 75°08’40”W, Sep 2018, J. Chuctaya. UFRGS 27447, 3, 40.4–47.3 mm SL, Río Ucayali, 05°34’42”S 74°29’42”W, Sep 2018, J. Chuctaya. UFRGS 27448, 1, 42.8 mm SL, Río Ucayali, near Galilea, 07°25’23”S 75°02’29”W, Sep 2018, J. Chuctaya. USNM 280541, 15 (3 c&s), 30.1–41.5 mm SL, Río Ucayali, 08º31’S 74º22’W, R. P. Vari, H. Ortega & A. G. Gerberich & J. A. Louton. Madre de Dios. MUSM 28147, 9, 39.6–43.0 mm SL, Tambopata, Cantera Cachuela Huesembre, 12º33’23”S 69º10’04”W, 5 Sep 2006, S. Martinez.

Figures

FIGURE 4 | Map of central and northern South America showing the distribution of Amblystilbe howesi (red dots), Prodontocharax melanotus (yellow dots) and P. aquilaepinnae (gray dots). Some symbols represent more than one lot or locality. Stars represent the type localities. Red triangle represents the type-locality of P. alleni.

FIGURE 11 | Amblystilbe howesi. A. Holotype, ANSP 69070, 41.8 mm SL, Boca Chapare, Chimore River, Cochabamba, Bolivia. B. MCP 39868, 41.1 mm SL, Mamoré River at Cristo Rei district, Madeira River basin, Guajará-Mirim, Rondônia, Brazil. Photos: Luiz R. Malabarba.

FIGURE 12 | Amblystilbe howesi, MCP 39868, 38.7 mm SL. SEM image of left side upper and lower jaws teeth. A. Premaxilla (with at least two missing teeth). B. Maxilla. C. Dentary.

FIGURE 13 | Amblystilbe howesi. A. UFRGS 21765, 40.0 mm SL, B. UFRGS 21754, 33.0 mm SL, Juruá River, 2 km above mouth of Juburi, Carauari, Amazonas, Brazil. C. CAS 119050, paratype of Prodontocharax alleni, 28.1 mm SL, Ucayali River, Cashiboya, Ucayali, Peru. Photos: Luiz R. Malabarba.

FIGURE 14 | Collection locality of Amblystilbe howesi, near Contamana, Ucayali River basin, Ucayali, Peru.