Characidium crandellii Steindachner, 1915

Armbruster, Jonathan W., Lujan, Nathan K. & Bloom, Devin D., 2021, Redescription of the Guiana Shield Darter Species Characidium crandellii and C. declivirostre (Crenuchidae) with Descriptions of Two New Species, Ichthyology & Herpetology 109 (1), pp. 102-122 : 103-108

Characidium crandellii Steindachner, 1915

Figures 1B , 4–6

Characidium crandellii Steindachner 1915: 32 , Rio Miang, tributary Cotingo, Tacutu; Boa Vista, Rio Branco, Brazil.

Specimens examined.— Brazil: syntypes: NMW 62673 , 5 (2gm), 69260, 2 (1gm), Amazon River basin, Rio Miang , tributary Cotingo , Tacutu ; Boa Vista, Rio Branco , Brazil.

Guyana: AUM 28034 , 3 (0mo/me, 3 gm), 26.8–33.3 mm SL, Potaro-Siparuni , Essequibo River basin, Potaro River, Tumatumari cataract, S bank below old hydroelectric plant, 5.36333, –59.00111; AUM 28139 , 1 (0), 24.4 mm SL, Potaro-Siparuni , Essequibo River basin, Potaro River, Waratuk cataract, 5.25889, –59.40028; AUM 28184 , 1 (1mo/me, 1gm), 37.1 mm SL, Potaro-Siparuni , Essequibo River basin, Potaro River and tributaries, at Tukeit cataract, 4.99889, –59.53889; AUM 35582 , 7 (2mo, 1me), 26.4–29.1 mm SL, Cuyuni-Mazaruni (Region 7) , Mazaruni River basin, Whitewater Creek 6.8 km SW Bartica, 6.378, –58.67374; AUM 36957 , 12 (1mo/me, 8gm), 25.1–45.2 mm SL, Upper Demerara-Berbice (Region 10) , Essequibo River basin, Essequibo River at Kurukupari , E bank, 4.66149, –58.67519; AUM 36958 , 7 (0) 20.0– 23.6 mm SL, Upper Takutu-Upper Essequibo (Region 9) , Amazon River basin, Pirara River, tributary of the Ireng River , 3.5 km NNW Pirara, 3.6487, –59.68897; AUM 36959 , 1 (1mo/me, 1gm), 34.6 mm SL, Upper Takutu-Upper Essequibo (Region 9) , Amazon River basin, Moco-Moco River at Moco-Moco Hydro Power Station 18.8 km SE Lethem, 3.29672, –59.64466; AUM 36960 , 5 (2mo/me, 2gm), 47.4–48.6 mm SL, Upper Demerara-Berbice (Region 10) , Essequibo River basin, Essequibo River at Kurukupari , E bank, 4.66149, –58.67519; AUM 45273 , 1 (0), 30.0 mm SL, Potaro-Siparuni (Region 8) , Essequibo River basin, Essequibo River , side channel in rapids, 4.4215, –58.48623; AUM 45348 , 1 (0), 23.7 mm SL, Potaro-Siparuni (Region 8) , Essequibo River basin, Essequibo River , side channel in rapids, 4.4215, –58.48623; AUM 45371 , 4 (0mo/ me, 4gm), 23.8–27.0 mm SL, Potaro-Siparuni (Region 8) , Essequibo River basin, Essequibo River , side channel in rapids, 4.4215, –58.48623; AUM 62834 , 1 (0), Potaro-Siparuni (Region 8) , Essequibo River basin, Kuribrong River, in rapids at Grass Shoals , 5.40791, –59.53179; AUM 62874 , 7 (0mo, 4me, 4gm), 37.2–43.8 mm SL, Potaro-Siparuni (Region 8) , Essequibo River basin, Kuribrong River, at Ram Sheep Rapids , 5.44236, –59.50201; AUM 62889 , 1 (0), Potaro-Siparuni (Region 8) , Essequibo River basin, Grass Falls Creek [Kiwikparu Creek], just upstream from mouth of Kuribrong River , 5.4065, –59.53361; AUM 62898 , 76 (8mo, 6me, 24gm, 6cs), 41.7–56.5 mm SL, Potaro-Siparuni (Region 8) , Essequibo River basin, Grass Falls Creek [Kiwikparu Creek], near top of falls, 5.40532, –59.5439; AUM 63165 , 2 (0), 23.1–24.3 mm SL, Upper Takutu-Upper Essequibo (Region 9) , Amazon River basin, Ireng River , 6.9 km WSW Karasabai, 4.01957, –59.6017; AUM 67037 , 3 (2mo, 3me, 3gm, 1cs), 47.4–72.5 mm SL, Potaro-Siparuni (Region 8) , Amazon River basin, Ireng River, at Orinduik Falls , between upper and lower falls, 4.72536, –60.03852, 2 January 2016; AUM 67142 , 1 (1mo, 1me, 1gm), 106.9 mm SL, Potaro-Siparuni (Region 8) , Amazon River basin, Ireng River, shoals at mouth of Monkey Creek , Kaibarupai , 5.04398, –59.97717, 9 January 2016; ROM 91332 , 3 (0), Potaro-Siparuni (Region 8) , Essequibo River basin, Sheetrock Creek at crossing of Wailang-Powis tractor trail, 5.47473, –59.43770; ROM 91410 , 1 (0), Potaro-Siparuni (Region 8) , Essequibo River basin, Mikobe Creek approximately 0.5 km upstream from mouth, at rapids beyond first rapid blocking upstream boat movement, 5.41396, –59.47025, October 201; ROM 110044 , 2 (0), Potaro-Siparuni (Region 8) , Essequibo River basin, Sheetrock Creek at crossing of road between Wailang and Mona Falls, 5.47494, –59.43769; ROM 101902 , 1 (0), Cuyuni-Mazaruni (Region 7) , Mazaruni River basin, no common locality given, 6.13585, –60.0745 .

Venezuela: AUM 39466 , 1 (1mo, 1me, 1gm), 49.4 mm SL, Amazonas, Orinoco River basin, Río Ventuari, above Salto Tencua , 58 km ESE of San Juan de Manapiare, 5.04777, –65.61583 ; AMNH 91171 , 21 (0mo/me, 10gm), Bolivar, Orinoco River basin, Río Carapo , at third rapids above camp along left bank, 5.71333, –63.53333 (coordinates per Armbruster and Taphorn, 2013).

Diagnosis.— Characidium crandellii can be distinguished from all crenuchids except C. declivirostre , C. duplicatum , new species, and C. wangyapoik , new species, by having the venter without scales from the isthmus to the pelvic girdle (vs. maximally to pectoral-fin insertion) and from most species of Characidium by having a very large pectoral fin with the first four unbranched pectoral-fin rays thickened, and the first pectoral-fin ray bent at an oblique angle (vs. pectoral-fin rays not thickened and first ray either straight or slightly convex). Characidium crandellii can be distinguished from C. declivirostre , C. duplicatum , new species, and C. wangyapoik , new species, by having the dorsal fin strongly falcate or concave (vs. largely rectangular with slightly convex edge); dorsal fin with a terminal hyaline band followed by a wide, dark band approximately 25% or greater the width of the fin, another wide hyaline band ~ 50% of the width of the fin, and a basal, dark band with all dark colors present on rays and membranes (vs. two or more thin dark bands much less than 25% of fin width, spots forming bands present only on fin rays); by having the pectoral fin either uniformly dark or with a lighter middle (vs. having spots forming two or more bands), by having the adipose fin inserted directly above insertion of the posteriormost anal-fin ray or slightly behind (vs. over the middle of the anal-fin base), by having 12 circumpeduncular scales (vs. 10), having dentary and premaxillary teeth wide and tri- to pentacuspid (central cusp longest; vs. teeth narrow and peg-like, and maximally tricuspid with only the central cusp well developed), by many teeth (.5) in the posterior dentary row (vs. usually zero but up to two total); and by an anal–apex length/SL ratio of 89.4–94.0 (vs. 93.9–100.3); from C. declivirostre and C. wangyapoik , new species, by having four branched pectoral-fin rays (vs. 3) and a preanal length/SL ratio of 72.9–76.6 (vs. 76.9–82.3); and from C. duplicatum , new species, by having one anterior branched pelvic-fin ray and ray count of i,6,i (vs. two, and ray count of ii,5,i). In addition, infraorbitals 3–4 are reduced to just ossification around the infraorbital canal in C. crandellii , while there is some laminar bone dorsal and ventral to the canal in C. declivirostre , C. duplicatum , new species, and C. wangyapoik , new species.

Description.— Measurements ( Table 1 ) and meristics (reported below) based on 20 specimens. Dorsal profile of body convex arc from tip of snout to posterior end of dorsal fin (highest point of arc at dorsal-fin origin); body then relatively straight and angled ventrally to adipose fin, then shallowly concave to caudal fin. Ventral profile straight to anal fin, then concave arc to caudal fin. Body depth greatest at dorsal-fin origin and least at middle of caudal peduncle. Body oval in cross section anteriorly with ventral surface flattened and oval with dorsal and ventral surfaces somewhat flattened on caudal peduncle. Eye diameter 45.8–97.3% snout length, decreasing with SL ( Fig. 3 ); oval, angled with anterior vertex ventral to posterior vertex; dorsal rim of orbit slightly higher than interorbital surface. Snout broadly rounded. Gill membranes united across isthmus. Tubercles absent.

Scales cycloid, mostly smooth, some with numerous (~ 20– 30) weak, parallel striae. Lateral line complete with anterior segments within each scale occupying approximately one-third length of each scale and pores visible laterally, vs. posterior segments occupying less than one-quarter length of each scale and pores covered by previous scale; 30 (2), 31 (3), 32 (8), 33 (6), or 36 (1) lateral-line scales; lateral-line scales distinctly smaller anteriorly; naked area located between anterior lateral-line scales and pectoral-fin base; lateral line continues onto scales covering caudal base. 4 (12) or 5 (8) scales above lateral line, 1 (2) or 2 (18) scales below lateral line, 12 circumpeduncular scales. Scales covering anterior 20% of caudal fin. 8 (2), 9 (6), 10 (9), or 11 (3) predorsal scales. Venter unscaled on isthmus and posteriorly to about 2 scales before pelvic-fin origin.

Dorsal fin with 2 unbranched and 8 (9) or 9 (11) branched rays (ii,8–9); first unbranched ray about half length of second; first branched ray longest with shortest ray in middle making fin falcate. Pectoral fin with 4 unbranched and 11 (11) or 12 (9) branched rays (iv,11–12); unbranched rays and first unbranched ray with thick pads of tissue anteriorly; first unbranched ray strongly bent in middle to form oblique angle; first branched ray longest and last shortest; pectoral fin oriented obliquely on body with insertion of posteriormost fin ray located posterodorsally to origin. Pelvic fin with 1 leading unbranched ray, 6 branched rays, and 1 posterior unbranched ray (i,6,i); first branched ray longest; 2 or 3 pelvic axillary scales present with complex covering about half of pelvic-fin base. Anal fin with 2 unbranched rays and 5 (4) or 6 (16) branched rays (ii,5–6); first unbranched ray approximately one-third length of second, closely adhered; fin falcate with first unbranched ray longest and last shortest. Caudal fin with 1 unbranched and 9 (17) or 10 (3) branched rays in upper lobe and 7 (6), 8 (12), or 9 (2) branched and 1 unbranched ray in lower lobe (i,9–10,7–9,i); forked with upper and lower lobes equal. Adipose fin present with base centered on vertical over last ray of anal fin. Rays of paired, dorsal, and anal fins with thick flaps of skin dorsally (paired fins) and laterally (dorsal and anal fins) that overlap successive rays in folded fin; flaps widest and longest anteriorly, decreasing in size and width posteriorly and usually absent on posterior rays.

Teeth tri- to pentacuspid, wide with edges sharp. 5 (3), 6 (6), 7 (8), or 8 (3) premaxillary teeth. 5 (1), 6 (1), 7 (4), 8 (3), 9 (5), 10 (2), 11 (2), or 12 (2) teeth in outer dentary row. Inner dentary row made up of many small, unicuspid teeth. Ectopterygoid with 2 rows of approximately 8–10 minute teeth per row.

Branchiostegal rays 4; 1 ray attached to posterior ceratohyal; 3 rays attached to anterior ceratohyal. Gill rakers 3–5 on dorsal limb, 1 on angle, 7–8 on ventral limb of anterior branchial arch. One supraorbital present; moderately crescent shaped with ventral edge almost straight; from dorsal midpoint of orbit to dorsal ~ 1/4–1/3 anterior scleral ossicle; one individual had the posterior portion of each supraorbital present as three separate ossifications in addition to main anterior ossification. All elements of infraorbital series, except infraorbital 1, without laminar component; infraorbitals 3–4 no more than ossification around canal. Parietal branch of supraorbital sensory canal extending to middle or about 3/4 of parietal. Parietal fontanel variable from tiny triangle at posterior borders of parietals to narrow opening at posterior borders of parietals that widens in posterior ~ 1/3 of parietals then narrows to contact with frontals. Frontal foramina above supraorbital canal 4, wide, circular.

Total number of vertebrae 35 (2), 36 (2), 37 (2). Vertebral centra 2 þ 3 fused, without ventral processes. Rib of centrum 4 distally expanded, extending anteriorly toward lateral process of centrum 2. Posterior chamber of swim bladder absent. Supraneurals between neural spine of fourth centrum and anterior dorsal-fin pterygiophore 4 (4), 5 (1). Epurals 2. Uroneural present, about 60% as long as urostyle.

Coloration in life.— ( Figs. 4 , 5 ) Background color generally light tan on body to yellow on fins occasionally with some green iridescence. Background color of largest specimen

(AUM 67142) golden with gold filling lighter areas of fins and gold present on ventral surface (although lighter) from anterior of the pelvic fins to caudal peduncle. Dark midlateral stripe generally present from opercle to caudal fin; scales within stripe darkest in their centers making stripe appear to be made out of chevrons with distal portions of some of these chevrons bleeding into scales above and below (darker above than below); stripe widens to large spot on caudal peduncle. About seven dorsal saddles present, first two in nuchal area, third below anterior portion of dorsal fin, fourth and fifth in interdorsal area, and sixth and seventh between adipose and caudal fin. Scales in lighter areas between saddles have posterior halves dark with darker colors dorsally. Irregular blotches present below lateral stripe and often contiguous with dorsal saddles. Light areas of body rich tan above midlateral stripe and pale yellow below; tan above stripe fades to pale yellow posteriorly. Head with mottled dark patch above roof of cranium, dark line behind the eye, dark line leading from near snout tip to posterior of eye, mottling dorsally on the snout with pale yellow spot located anterodorsally to eye, and lighter areas of the cheek and opercle speckled with melanophores. All fins gray at distal margins and yellow proximally; gray and yellow portions bleed into one another along fin rays. Membranes and some parts of rays between gray and yellow regions dark; most intense dark marks on dorsal fin, ventral portion of caudal fin, and at bases of pectoral and adipose fins. Unbranched pectoral and pelvic rays (and less so following branched rays) with darkest colors centrally along rays and increasing distally, with anterior margins gray and posterior margins yellow. Ventrally, colors more muted; thickened, unbranched and anterior branched rays of pectoral and pelvic fins light gray. Dark areas located at bases of all fins. Largest specimen (AUM 67142) differs from this general pattern in that light areas golden and dark areas more intense, lateral stripe absent, and iris brick red (vs. reddish but mottled with black).

Coloration in alcohol.— Similar to color in life, but dark areas more intense and wider and light areas light gray or tan.

Distribution.— Characidium crandellii has been found mostly in the upper Branco River (Amazon River) basins of Brazil and Guyana and the middle and lower Essequibo River of Guyana ( Fig. 6 ). The type locality is a tributary of the Cotinga River (tributary of the Takutu/Branco) in the vicinity of Boa Vista ( Fig. 6 ). We have examined two collections of the species from the Orinoco River basin. One specimen is from above Tencua Falls (Salto Tencua), the first major barrier to navigation and a major faunal break between the middle and upper Ventuari River ( Lujan et al., 2018), and the other collection is from south of Tepuy Guaiquinima in the Paragua/Caroni River basin, also above a series of rapids, including Uraima Falls located just north of the tepui. The Tencua specimen differs from other C. crandellii sensu stricto by having a series of small, vertical spots below the midline and just posterior to the pectoral fin and only the faint remnant of a lateral stripe. The Río Paragua specimens appear more similar to the specimens from the Amazon and Essequibo than to the Tencua specimen.

Remarks.— One specimen from the Ireng River (AUM 67142; 106.9 mm SL; Fig. 4 ) is the largest specimen of Characidium ever examined and far larger than any other specimens. Its golden color seems to suggest that it is a nuptial male, but we did not confirm with dissection because the specimen is unique.

Figures

FIG. 1. Thickened, keratinized pads on the undersurface of the anterior pectoral-fin rays of (A) Characidium wangyapoik, new species, CSBD F-3615, holotype, and (B) C. crandellii, AUM 67142. Photos by N. K. Lujan.

FIG. 4. Dorsal, lateral, and ventral views of Characidium crandellii in life, potential nuptial male, AUM 67142, 106.9 mm SL; Ireng River population. Photos by N. K. Lujan.

FIG. 5. Dorsal and lateral views of Characidium crandellii in life, common coloration, AUM 62874, 57.0 mm SL; Kuribrong River population. Photos by J. W. Armbruster.

FIG. 6. Distribution of Characidium crandellii, type locality indicated with T.

FIG. 3. Plot of the ratio of orbital diameter to head length versus standard length for all measured specimens of fast-water Characidium of the Guiana Shield showing allometry in eye size.