Brachyhypopomus walteri Sullivan, Zuanon & Cox Fernandes 2013

This species can be distinguished by having the following combination of characters: distinct patch of brown pigment below skin at base of orbit; body yellow and semi-translucent in living specimens; caudal filament long and fine, greater than 20% of LEA (length from the tip of thesnout to the posterior end of the anal-fin base) in intact specimens; electric discharge organ (EOD ) pulse duration very long (between 3.5 and 4 milliseconds at 25° C) with head-positive first phase of longer duration than second head-negative phase in both sexes (Ref. 94132).

Usually found in floating meadow habitats, composed mostly of the grass Paspalum repens, Poaceae. Occurs mainly in white water, but also in areas near the confluence of black water rivers with the Amazonas/Solimões ranging from low to medium conductivity. Syntopic with the species of Eigenmannia, Gymnotus, the apteronotid Parapteronotus hasemani and the electric eel Electrophorus electricus in the floating meadow habitats (Ref. 94132).

Brachyhypopomus walteri is a species of electric knifefish. The species was discovered in the Central Amazon.

Brachyhypopomus walteri, denominada comúnmente morenita en Paraguay y cuchillo en Bolivia y Ecuador,​ es una especie del género de peces de agua dulce Brachyhypopomus, de la familia de los hipopómidos. Habita en ambientes acuáticos tropicales y subtropicales en el centro y centro-sur de Sudamérica.

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Brachyhypopomus walteri Brachyhypopomus generoko animalia da. Arrainen barruko Hypopomidae familian sailkatzen da.

沃氏短身電鰻，為輻鰭魚綱電鰻目短吻電鰻科的其中一種，為熱帶淡水魚，分布於南美洲亞馬遜河流域，體長可達17.5公分，棲息在底中層水域，生活習性不明。

Morphometric and meristic data are presented in Tables 1, 3 and 4. A Brachyhypopomus of moderate to small adult size for a hypopomid; largest specimen examined measures 175 mm TL, 125 mm LEA. Body very compressed, depth at posterior end of abdominal cavity 2.7–3.1 times body width. Body more compressed posteriorly, sides of body with only slight curvature posterior to abdominal cavity. Dorsal profile gently convex. Depth quickly tapers posteriorly: depth of body at 40th post-abdominal vertebra 36–41% depth at first abdominal vertebra. Head short in comparison to body length, deep and wide: HL 11.2–12.6% LEA, head depth at occiput 72–81% HL, head width at opercle 54–63% HL. Head triangular in lateral view, dorsal profile of head straight from occiput to point of downturn of snout, ventral profile of head straight from lower jaw to opercular area with little if any concavity between opercular area and tip of lower jaw. Eye moderate in size, 12.4–14.5% HL. Mouth small, terminal, jaws equal, gape 20–23% HL. Closed lips meet ventral to a horizontal through ventral margin of eye. One to five small needle–like conical teeth present on each premaxilla (Fig. 1), lower jaw edentate. Maxilla moderate in length, thin, with slight curvature. Snout moderate in length, 26–29% HL, edge of upper lip close to farthest anterior extent of snout. Posterior naris close to eye, posterior naris–eye 1.8–3.7% HL. Lateral ethmoid present. Round ossification present in anterior portion of palatine cartilage (Fig. 1). Infraorbital portion of cephalic lateralis system incomplete, lacking recurrent anterodorsal segment and associated pores beneath and anterior to the posterior nares that are present in most other Brachyhypopomus (see fig. 53 in Sullivan 1997); fourth supraorbital pore lying near vertical through posterior nostril, pores inconspicuous. Preopercular lateral-line canal embedded in preopercle, canals radiating out to pores. Pores of lateral-line canal immediately behind head without downward pointing tubes. Discernible lateral scales terminate along caudal filament. Five branchiostegal rays, medialmost two thin with blades oriented nearly vertically compared to outer three (see diagnosis of Odontohypopomus). Gill rakers robust for genus, some with weakly ossified cores, on anterior faces of first four gill arches. Rakers subtended on ceratohyals one to four by small trough-shaped ossicles. Approximately 40 gill filaments on arch one. Three pectoral radials, all partially fused together at proximal end. Mesocoracoid bridge absent. Pectoral fin broad, 12–15 branched plus unbranched rays, length 5.3–7.0% LEA. 198–216 anal fin rays, longest rays 4.0–4.9% LEA. Precaudal vertebrae 13–16, up to 75 caudal vertebrae in advance of regenerated portion of caudal filament. Body excluding head and fins covered with thin cycloid scales, small dorsally, larger posterolaterally, partially obscured by skin. Twelve scale rows above, 13 scale rows below lateral line at farthest extent of pectoral fin. Anal-fin origin slightly posterior to vertical at midpoint of extended pectoral fin. Caudal filaments long and fine in intact mature specimens, 20–32% of TL. Sexual dimorphism of caudal filaments not observed. Three or four bilateral columns of electrocytes along caudal filament, number often alternating along length of caudal filament; 38–63 rows of electrocytes. Electrocytes do not extend farther anteriorly than base of urogenital pore. No accessory electric organs on head or humeral region. Summary of morphometric measurements for Brachyhypopomus walteri sp. n. (included are holotype and ten paratypes identified from radiographs as undamaged at anal-fin terminus). Measurement holotype range mean S.D. N Total length (TL) (mm) 163.0 116–175 153.2 15.3 11 Length to end of anal fin (LEA) (mm) 126.0 85–127 111 13 11 Head length (HL) (mm) 14.4 10.3–14.5 13 1.4 11 Caudal filament length (% TL) 22.7 19.6–31.8 27.3 3.5 11 Proportion of LEA (%) Head length 11.4 11.2–12.6 11.7 0.5 11 Snout to occiput 8.5 7.9–9.6 8.9 0.5 11 Snout to anal fin origin 19.9 18.4–21.2 19.6 0.9 11 Depth at 1st post-abdominal vertebra 12.2 10.5–13.2 12 0.8 11 Depth at 20th post-abdominal vertebra 9.4 8.5–10.0 9.4 0.5 11 Depth at 40th post-abdominal vertebra 4.7 4.4–5.2 4.7 0.3 11 Caudal filament base depth 1.9 1.6–2.1 1.8 0.2 11 Longest anal fin ray 4.6 4.0–4.9 4.5 0.2 11 Longest pectoral fin ray 5.4 5.3–7.0 6.1 0.6 11 Proportion of HL (%) Snout length 28.5 25.7–29.0 27.4 1.2 11 Gape 22.9 19.8–23.2 21.5 1.4 11 Orbital diameter 12.5 12.4–14.5 13.5 0.7 11 Interorbital distance 23.9 21.7–26.5 24 1.6 11 Posterior naris-eye 3.4 1.8–3.7 2.8 0.7 11 Branchial aperture 29.7 23.8–30.6 26.9 2.6 11 Head width at opercle 63.3 54.4–63.3 58.8 3.2 11 Head width at eye 42.2 40.1–43.8 41.9 1.3 11 Head depth at occiput 79.0 72.1–80.9 76.4 3.1 11

See distribution map (Fig. 5). Brachyhypopomus walteri sp. n. is known only from the Amazon basin where it appears to be common in floating meadow habitats, (mostly composed of the grass Paspalum repens, Poaceae), on the margins of the Amazonas/Solimões and its tributaries. It has been collected predominantly in white water, but also in areas near the confluence of black water rivers with the Amazonas/Solimões ranging from low to medium conductivity. Apart from one collection very near Manaus and the white water Rio Branco, it is absent from collections in the Rio Negro system. It is frequently taken with Brachyhypopomus bennetti sp. n. and sometimes with Brachyhypopomus brevirostris. Species of Eigenmannia, Gymnotus, the apteronotid Parapteronotus hasemani and the electric eel, Electrophorus electricus, frequently co-occur in the floating meadow habitats preferred by this species.