Auchenipterichthys coracoideus (Eigenmann & Allen, 1942)

Figs. 1-5

Auchenipterichthys thoracatus (not of Kner, 1857), Eigenmann & Eigenmann, 1888: 154 [in listing of South American catfishes; specimens from Coary (=Coari) and Hyavary (=Javari), Brazil]. – Eigenmann, 1910: 396 [in listing of South American fresh water fishes; specimens from Coary (=Coari) and Hyavary (=Javari), Brazil]. – Eigenmann & Eigenmann, 1890: 282 [redescription of A. thoracatus, erroneously based on specimens of A. coracoideus; Coary (=Coari) and Hyavary (=Javari), Brazil]. – Fowler, 1951: 458 [in part, citations of species from outside of upper rio Madeira basin]. – Mees, 1974: 3 5 [i n p a r t, n o t s y n o n y m y o f Trachycorystes coracoideus into Auchenipterichthys thoracatus; not citations of Auchenipterichthys coracoideus from outside of upper rio Madeira basin; not cited specimen from Peru]. – Ortega and Vari, 1986: 114 [in listing of freshwater fishes of Peru].

Trachycorystes coracoideus Eigenmann & Allen, 1942: 44 and 120 [type-locality: Peru, Iquitos; syntypes: CAS 63746 (3)]. – Gosline, 1945: 458 [based on Eigenmann & Allen, 1942]. – Fowler, 1945: 64 [in listing of species of fishes in Peru]. – Fowler, 1951: 473 [literature compilation].

Auchenipterichthys longimanus (not of Günther, 1864), Mees, 1974: 38 [in part, specimen from Nazareth, Peru].

Auchenipterichthys thoracatum (not of Kner, 1857), Merona et al., 1987: 83 [Brazil, lower rio Tocantins; increasing relative abundance following closure of Tucuruí dam].

Auchenipterichthys coracoideus, Ferraris, 2003: 472 [checklist].

Diagnosis. A species of Auchenipterichthys with coracoid bone covered only by thin layer of integument and exposed ventrally (Fig. 1a), an obliquely truncated caudal-fin margin, typically 25 or fewer branched anal-fin rays (rarely 26; Table 1), eight branched pelvic-fin rays, anterior teeth on the premaxilla visible when the mouth is closed, and the body pigmentation dark gray dorsally and lighter (pale in some specimens) laterally and ventrally, body without distinct dark spots. Auchenipterichthys coracoideus is most similar in appearance to A. thoracatus, which typically has 26 or more branched anal-fin rays, and is readily distinguished from its other two congeners, A. longimanus and A. punctatus, which have coracoids that are covered ventrally by a thick layer of integument (Fig. 1c), the anterior teeth on the premaxilla that are not visible when mouth is closed and, typically, nine branched pelvic-fin rays.

Description. Body depth at dorsal-fin origin 0.23–0.26 of SL and slightly greater than body width at cleithrum. Body depth at anal-fin origin 0.23–0.25 of SL. Body compressed, with width at anal-fin origin 0.39–0.41 of body depth at that point. Ventral surface of coracoids exposed on ventral surface of body (see Fig. 1a). Lateral line complete and midlateral. Canal having irregular zigzag pattern, with oblique, posteriorly-directed branches extending off main canal. Lateral line canal extending short distance onto, and obliquely posterodorsally-directed on, caudal-fin base.

Head depressed anteriorly; depth of head at vertical through middle of orbit approximately one-half of head width at middle of orbit. Head length 0.36–0.39 of SL. Dorsal profile of head broadly convex anteriorly and then straight from vertical running through anterior margin of orbit to dorsalfin origin. Distance from midpoint of snout to anterior margin of orbit slightly greater than horizontal diameter of orbit. Snout margin broadly rounded from dorsal view. Interorbital width approximately 0.55–0.58 of HL and approximately equal to distance from middle of eye to posterior margin of opercle. Eye large, lateral, and visible in both dorsal and ventral views. Orbit distinctly ovoid with horizontal axis longer.

Barbels slender and thread-like. Maxillary barbel long, extending posteriorly slightly past margin of opercle. Medial mandibular barbel originating immediately posterior of lower lip; adpressed barbel extending posteriorly to point slightly short of vertical through transverse plane through origin of lateral mandibular barbel. Lateral mandibular barbel originating in plane slightly anterior of vertical through middle of orbit and extending posteriorly approximately to anterior portion of exposed cleithrum.

Branchiostegal membrane broadly attached to isthmus; ventral margin of gill opening extending to anterior margin of exposed portion of cleithrum.

Mouth terminal, but with upper jaw extending slightly beyond margin of lower jaw. Anterior premaxillary teeth visible from ventral view when mouth is closed. Teeth on premaxilla minute and arranged in band. Band consisting of approximately 8 irregular series of teeth at symphysis and of 10 irregular series laterally. Dentary teeth slightly larger than those on premaxilla, with approximately 6 series of teeth at symphysis that progressively decrease to one tooth row posterolaterally.

Dorsal-fin origin at 0.37 of SL. Length of dorsal-fin base approximately one-half of length of first branched dorsalfin ray. Dorsal-fin spine pungent and slightly curved with convex anterior margin. Length of dorsal-fin spine approximately equal to HL except in nuptial males in which spine may be longer than 1.5 times HL. Basal half of anterior margin of dorsal-fin spine bearing two rows of small, blunt projections. Spine margin smooth or finely serrated distally. Posterior margin of spine with few, short, medial, obliquely distally-directed serrae; serrae proportionally longer in nuptial males. Dorsal-fin rays II,6. Adipose fin relatively small.

Caudal fin obliquely truncate with dorsal most branched ray longest. Principal caudal-fin rays i,7,8,i.

Anal-fin base approximately 0.24–0.27 of SL.Anal-fin origin located distinctly posterior of middle of SL and at, or slightly posterior of, middle of TL. Anal-fin margin straight, with first ray longest and subsequent rays becoming progressively shorter, but with anterior rays in nuptial males extending beyond margin of rest of fin. Last anal-fin ray without membranous attachment to caudal peduncle.Anal-fin rays iii,20 to iii,26 (Table 1).

Distal margin of pelvic fin broadly convex with third branched ray longest. Pelvic-fin insertion at middle of SL. Tip of adpressed pelvic fin falling short of anal-fin origin. Pelvicfin rays i,8 (Table 1).

Pectoral fin with strong spine serrated along entire length of both margins. Serrae antrorse along anterior margin of spine and retrorse along posterior margin. Anterior pectoral-fin rays longest. Fin margin straight anteriorly and convex along posterior rays. Pectoral-fin rays typically I,8, rarely I,7 or I,9 (Table 1).

Pigmentation pattern in alcohol. Overall ground coloration most often grayish, with overall coloration darker on dorsal portion of head and body and in some individuals on midlateral portion of body posterior of head in region overlying swim bladder. Overall pigmentation pattern less intense in some individuals, most notably those from some locations in western portions of species distribution, albeit without any distinct geographic pattern to differences in coloration. Abdomen unpigmented. Snout, upper lip, and region ventral of margin of lower lip very dark in many, but not all, specimens.

Lateral and dorsolateral surface of body with several series of vertically-aligned, unpigmented, rounded spots of size most often approximately equal to one-fifth to one-quarter width of pupil or smaller. These series begin most often under, but in some individuals somewhat anterior of, base of dorsal-fin spine and extend posteriorly to beyond posterior terminus of base of adipose fin. Spots often difficult to discern in specimens of overall light ground pigmentation. Midlateral surface of body with irregular longitudinal series of unpigmented spots extending from rear of head to posterior margin of caudal peduncle. Unpigmented spots coalesce in some individuals into larger spots of irregular form. Region anterior of vertical of pelvic-fin origin and ventral of midlateral series of unpigmented spots with few, scattered, unpigmented spots.

Patch of dark to very dark pigmentation typically present anterior to base of dorsal fin. First and second interradial membranes of dorsal fin dark distally. Adipose fin with dark basal spot continuous with dark pigmentation of body in most individuals, other specimens with diffuse batch of dark chromatophores basally that do not form distinct spot. Caudal fin distinctly dusky basally and continuing pigmentation of body. Region of dark pigmentation on base of caudal fin with distinct, straight to slightly irregular, posterior margin; margin somewhat anteroventrally inclined. Some specimens with small, unpigmented spots within dusky, basal pigmentation field in region overlying central rays.

Basal region of dark caudal-fin pigmentation followed by hyaline region and then vertical band of less intense dark pigmentation along distal margin of fin.Anal fin with variably developed dark pigmentation. Some individuals with distinctly darker basal band on caudal fin formed of dark chromatophores comparable in size and form to those on adjoining region of body; when present, darker field of pigmentation often extending more distally on dorsal rays of mature males. Other individuals with less developed dark pigmentation continuous across fin. Most specimens with distal portions of fin darker than middle sections of rays. Dorsal surface of pelvic fin with diffuse dark pigmentation in some individuals, but without distinct patch of dark pigmentation. Distal portion of fin with dark pigmentation in most individuals. Margins and sometimes dorsal surface of pectoral-fin spine dark. Pectoral-fin rays variably outlined with dark chromatophores.

Maxillary barbel somewhat to darkly pigmented dorsally; barbel pale ventrally. Mandibular barbels unpigmented.

Color pattern in life. Dark pigmentation as in preserved specimens. Lateral and posterodorsal surface of head along with lateral surface of anterior portion of body, dorsolateral surface of body and basal one-half of caudal fin with variably intense yellowish coloration. Yellow coloration also apparent on basal one-half of dorsal-fin spine and rays and on adipose fin (Fig. 2).

Sexual dimorphism. Auchenipterichthys coracoideus demonstrates sexual dimorphism in the length of the dorsal spine and anterior rays of the anal fin as discussed above (see Figs. 3 and 4).

Distribution. Tocantins River, central and upper portions of Amazon River, and Essequibo River basins (Fig. 5).

Remarks. Auchenipterichthys coracoideus was originally described as a species of Trachycorystes by Eigenmann & Allen (1942: 120) without a discussion of the basis for that generic assignment; however, the species is clearly a species of Auchenipterichthys . Auchenipterichthys coracoideus has been repeatedly misidentified as A. thoracatus by various authors who applied that name to samples of the genus with exposed coracoids that originated across the Amazon basin (see synonymies for those two species). All population samples of A. thoracatus examined in this study originated in a relatively restricted region in the upper portions of the Madeira River in eastern Bolivia and southwestern Brazil (Fig. 10; dots). We consequently treat all reports of A. thoracatus from the portions of the Amazon basin outside of the upper Madeira River system as A. coracoideus, which has a wide distribution across that river basin (Fig. 5).

In addition to the difference in the number of anal-fin rays between Auchenipterichthys coracoideus and A. thoracatus, the two species appear to differ in the shape of the head and the angle of divergence of the exposed portion of the coracoids. The ventral margin of the head of A. coracoideus is nearly horizontal, in contrast to the more oblique aspect of that region in A. thoracatus . The contralateral coracoids diverge more posteriorly in A. coracoideus, whereas they are more nearly parallel in A. thoracatus (see Figs. 1 a-b). However, we found it impossible to quantify these differences sufficiently well to include them in the diagnoses of the respective species.

Mees (1974: 36) reported a lot from Nazareth, Peru (FMNH 15502) as Auchenipterichthys longimanus . Examination of that material demonstrates that is it A. coracoideus .

Material examined. BRAZIL. Amazonas: lower rio Madeira, approximately 150 km up from mouth, Borba (4°23’S, 59°35’W), MZUSP 28351, 2 (50-56) . Rio Hyavary (= rio Javari), tributary of rio Solimões at the Peruvian-Brazilian border (4°21’S, 70°02’W), MCZ 7347, 4 (44–96) . Lago do Coari on rio Solimões, at Coari (4°08’S, 63°07’W), MCZ 7386, 1 (102) ; MCZ 7387, 12 (41-54); MCZ 7353, 1 (102), MCZ 7383, 1 (102), MCZ 7388, 1 (101), MCZ 7372 (plus parts of MCZ 7353, MCZ 7386, MCZ 7388), 15 (80–111; some specimens originally in four separate lots now inseparably mixed); CAS 76784, 1 (47); USNM 41529, 2 (88– 96) . rio Livramento, tributary of rio Madeira (7°17’S, 62°22’W), AMNH 12700, 8 (94–112) ; MCZ 34126, 1 (119) . Lago Terra Preta, Janauari (approximately 3°12’36"S, 60°01’56"W), USNM 275525, 5 (69–78) ; USNM 276526, 6 (53–65) . Goiás: rio Araguaia, lago Ressaca, Luís Alves (approximately 13°14’S, 50°35’W), MZUSP 53869, 1 (67) . Rio Araguaia, Lago Preto, Luís Alves (approximately 13°14’S, 50°35’W), MZUSP 54183, 2 (79–85) . Mato Grosso: rio Araguaia, MZUSP 44073, 3 (68–87) . Rio Araguaia, lago da Alvoradinha, MZUSP 53568, 1 (69) . Rio Araguaia, lago Montaria, MZUSP 53569, 4 (60–72) . Rio Araguaia, near Ilha do Biratã, MZUSP 62848, 1 (71) . Rio Araguaia, lago das Branquinhas, MZUSP 53570, 5 (73–81) . Pará: matas of igapó do rio Cinzento, tributary of rio Itacaiunas, MZUSP 52971, 1 (89) . Rondônia: lago Piauí, mouth of rio Jamari (8°27’S, 63°30’W), MZUSP 28377, 2 (114–122) . GUYANA. Pirara Creek, Apotorie, USNM 378826, 3 (41–49) . Guyana, no specific locality, USNM 317963, 1 (40) . PERU. Loreto: Iquitos (3°46’S, 73°15’W), CAS 63746, 1 (104; syntype of Trachycorystes coracoideus) , CAS 220574, 2 (104– 107; syntypes of Trachycorystes coracoideus) . Vicinity of Iquitos, río Nanay opposite naval base, backwater pools off Cocha (4 miles above Amazon River, approximately 3°46’S, 73°15’W), ANSP 139052, 13 (49–58) . Río Nanay (tributary of río Amazon) at Pampa Chica, village 4.54 km W of Iquitos (large beach along N Bank; 3°45’09"S, 73°17’00"W), ANSP 178446, 6 (55–94) . Yaguas Yacu, near Pebas (3°19’59"S, 71°48’59"W), SU 58655, 4 (42–65) ; SU 58659, 1 (54) . Río Nanay drainage, Zúngaro Cocha (3°49’S, 73°22’W), NRM 13516, 2 (36–41) . Río Samiria drainage, right bank muddy playa, 30 minutes upstream of Pithecia (5°13’S, 74°42’W), NRM 18577, 1 (58) . Caño Abico, tributary of río Samiria, approximately 6 to 7 km from mouth in río Marañon (4°55’S, 74°30’W), FMNH 111525, 6 (57–72) . Río Yavari, San Fernando, 100 m asl (4°09’S, 70°13’59"W), FMNH 96230, 2 (56–100) . Río Manite system, caño entering Río Manite about 10 km upriver of junction of Río Manite and río Amazonas (3°32’S, 72°40’W), USNM 284865, 1 (60) . Río Itaya, main river channel and lower portions of caños, 5 to 20 km upstream of Belen (Iquitos) (3°51’S, 73°12’W), USNM 284856, 1 (51) . Ucayali: Pucallpa, río Ucayali, Utuoquinia, USNM 273580, 3 (60–82) . Pucallpa, río Ucayali, Tacshitea (8°02’48"S, 74°39’19"W), USNM 273595, 5 (47-56) . District Coronel Portillo, Yarinacocha, opposite landing for town of Yarinacocha (8 °16’ S, 74°36’W), USNM 284849, 2 (59–80) . Inexact locality: Nazareth, FMNH 15502, 2 (42-43).