Donald C. Taphorn

Food habits of piranhas in the low llanos of Venezuela

Eight piranha species (Characidae: Serrasalminae) coexist in streams and pools of the western Orinoco River Basin Ilanos. The species differ in adult size, body form, and relative abundance. Examination of some 1300 specimens collected over a seven-year period (1979-1985) showed that food habits and diet diversity usually change with age. Small juveniles of the abundant and widespread Pygocentrus notatus eat microcrustaceans and aquatic insects. Above 40 mm standard length (SL), they take small fish and chunks of fish flesh. Small juveniles (20-80 mm SL) of six species (Serrasaimus altuvei, S. irritans, S. cf elongatus, S. rhombeus, S. caribe, and Pristobrycon cf striolatus) specialize in fins of other small fishes, but by 80 mm SL their diets shift to small fish, pieces of fish flesh, and fins. However, all sizes of Catoprion mento eat scales. Considerable diet overlap among different piranha species in the same size dasses suggests that plentiful food resources are not limiting. These savanna piranhas do not depend on fruits and seeds as has been reported for piranhas in flooded tropical rain forests.

Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield

Akawaio penak, a new genus and species, is described from the upper Mazaruni River, Guyana. The new species is diagnosed from all other species of Hypopomidae by several anatomical traits. The phylogenetic affinities of the new genus were inferred using data from one nuclear (rag2) and two mitochondrial (COI and cyt b) genes. The phylogenetic analyses indicate that Akawaio is the sister taxon of a clade that includes Brachyhypopomus, Hypopomus, Microsternarchus and Racenisia. These results provide evidence for the phylogenetic composition of Hypopomidae supported by previous molecular studies and support the position of the Steatogenini (Hypopygus + Steatogenys) as the sister group of Rhamphichthys + Gymnorhamphichthys. The description of this new electric knifefish increases the total number of endemic genera and species in the upper Mazaruni, a region that is suffering freshwater habitat degradation as consequence of gold‐mining activities.

A New Genus and Species of Weakly Armored Catfish from the Upper Mazaruni River, Guyana (Siluriformes: Loricariidae)

Paulasquama callis is a new genus and species of partially deplated ancistrin loricariid from the Waruma River, a tributary of the upper Mazaruni River, in northwestern Guyana. Paulasquama differs from all other described hypostomines by lacking plates in an oval area lateral to the mesethmoid, by having small plates in the dorsal series below the dorsal fin (less than half the typical size of other loricariids), and by having a fleshy keel on the preadipose plate and slightly anterior. The opercle of Paulasquama is sickle-shaped as in basal ancistrins, but has a posterior connection to the hyomandibula as in derived members of the Ancistrus clade.

Two New Species of Thicklip Thornycats, Genus Rhinodoras (Teleostei: Siluriformes: Doradidae)

Abstract Rhinodoras is newly diagnosed within Doradidae by its unique combination of coloration (sides darkly mottled, usually with wide dark bars, light midlateral stripe absent) and lip morphology (labial tissue thick, fleshy, considerably expanded at corners of mouth forming rounded flap-like extensions with entire margins, all surfaces rugose with low, rounded, and tightly spaced papillae, and distal margin of lower lip draped over bases of outer and inner jaw barbels, at times nearly encircling the latter). Three previously described species are considered valid, R. thomersoni (Lake Maracaibo basin), R. boehlkei (Amazonas), and R. dorbignyi (Paraguay–Paraná), and two new species are described. Rhinodoras armbrusteri from the Branco/Essequibo basins is diagnosed by having ventral surfaces with dark pigment, anterior midlateral plates moderately deep with dorsal and ventral wings subequal in depth, sum of midlateral plates 57–60, midlateral plates anterior to vertical through pelvic-fin origin usually five, tympanal portion of lateral-line canal moderately ossified with three distinct plates, postcleithral process moderately short and broad, adipose eyelid moderate to large, pectoral-fin rays usually eight, and one-part gas bladder. Rhinodoras gallagheri from the Orinoco basin is diagnosed by having ventral surfaces pale, anterior midlateral plates shallow to moderately deep with dorsal and ventral wings about equal in depth, midlateral plates anterior to vertical through pelvic-fin origin usually five, tympanal portion of lateral-line canal weakly ossified with two to three emergent plates, postcleithral process moderately long and narrow, adipose eyelid moderate to large, pectoral-fin rays usually eight, and one-part gas bladder. Rhinodoras is the only doradid genus with extant species in both trans- and cis-Andean drainages. Se actualiza el diagnosis del género Rhinodoras dentro de la familia Doradidae en base a su patrón de coloración; éste que consiste en lo siguiente: costados oscuramente moteados, carencia de una franja media lateral clara, y generalmente posee tres franjas verticales oscuras; estos caracteres en combinación con una morfología labial especial que en tener el tejido labial grueso, carnoso, y expandido considerablemente en las esquinas de la boca para formar una solapa redondeada sin borde aserrados; la superficie de este tejido es rugosa, con papilas bajas, redondas y casi tocándose entre si; el margen distal del labio inferior pasa por encima de las bases de las barbillas mentonianas externas e internas, a veces casi encierran a éstas últimas. Se consideran válidas tres especies previamente descritas: R. thomersoni (cuenca del Lago de Maracaibo), R. boehlkei (Amazonas), and R. dorbignyi (Paraguay–Paraná), y se describen dos especies como nuevas. Rhinodoras armbrusteri del cuencas del Branco/Essequibo se distingue en poseer las superficies ventrales con pigmento oscuro, las placas laterales medias anteriores son moderadamente profundas y con las alas dorsales y ventrales desiguales en altura; la suma de los conteos de las placas medias laterales de ambos lados oscila entre 57 y 60; presenta cinco placas medias laterales anteriores hasta llegar al nivel del origen de las aletas pélvicas; la porción encima del tímpano del canal de la línea lateral está bien osificada y consiste de tres placas distintas; el proceso postcleitral es moderadamente corto y ancho; el ojo es de moderado a grande, los radios pectorales generalmente son ocho, y la vejiga natatoria presenta una sola cámara. Rhinodoras gallagheri del cuenca del Orinoco se distingue de las otras especies del género porque tiene las superficies ventrales claras, las placas medias laterales anteriores son de poca profundidad o de profundidad moderada y con las alas dorsales y ventrales más o menos iguales en altura, cinco placas medias laterales anteriores hasta el nivel de las aletas pélvicas, la porción encima del tímpano del canal de la línea lateral es pobremente osificada, con dos o tres placas emergentes; el proceso postcleitral es moderadamente largo y estrecho, el ojo es de moderado a grande, los radios pectorales usualmente son ocho, y la vejiga natatoria y tiene una sola cámara. Rhinodoras es el único género de doradidos existente que habita cuencas en ambos lados de los Andes.

New Species of Rhynchodoras from the Río Orinoco, Venezuela, with Comments on the Genus (Siluriformes: Doradidae)

Abstract A new species of proboscoid thornycat, Rhynchodoras castilloi, is described from the Río Apure, Orinoco basin, Venezuela. The new species is distinguished from R. woodsi (Essequibo and Amazon basins minus Xingu and Tocantins basins) by having a simple gas bladder (vs. each posterior chamber of gas bladder expanded into elongate horn-like diverticulum) and tubercles punctate and abundant (vs. tubercles elongate, dash-like, and sparse). The new species is distinguished from R. xingui (Xingu and Tocantins basins) by having all three tympanal scutes weakly developed (vs. second and particularly third well developed, latter with medial carina), midlateral scutes modally 35 per side, range 34–36 (vs. 34, range 33–34), and anterior midlateral scutes relatively shallow, depth about one-fifth (vs. about one-third to one-quarter) of corresponding body depth, with weakly developed dorsal and ventral laminae lacking distinct serrations along posterior margins (vs. dorsal and ventral laminae of midlateral scutes well developed with conspicuously serrated posterior margins). The type species, R. xingui, is distinguished from R. woodsi by having a simple gas bladder (vs. with two posterior horn-like diverticula), midlateral scutes modally 34 per side, range 33–34 (vs. 35, range 34–37), and anterior midlateral scutes with conspicuous medial thorns (vs. thorns absent or weak, procumbent). Notable features of the genus are discussed, including jaw and gas bladder morphology, development of anterior nuchal plate, presence of multiple pores in skin beneath postcleithral process, and tubercle morphology and distribution. Shared derived characters suggest a sister-group relationship between Rhynchodoras and Rhinodoras plus Orinocodoras.

A new species of Gelanoglanis (Siluriformes: Auchenipteridae) from the Marañon River (Amazon Basin), northeastern Perú

ABSTRACT We describe a new species of driftwood catfish, Gelanoglanis travieso, (Siluriformes: Auchenipteridae) from the Marañon River, a whitewater tributary of the Amazon River in northeastern Perú. It shares with the two described species in this genus, G. stroudi, from left bank whitewater tributaries of the Orinoco River in Colombia and Venezuela, and G. nanonocticolus from blackwater tributaries of the upper Orinoco and Negro Rivers in Amazonas, Venezuela and northern Brazil, the following synapomorphies: reduced size, compressed body, conical snout, a single pair of mental barbels, premaxillae widely separated at rostral border of upper jaw, premaxillary and dentary tooth patches narrow, posterior naris long and narrow and positioned immediately anterior to orbit, and small eyes. Gelanoglanis travieso differs from all congeners in having second dorsal-fin lepidotrichium filamentous, simple, not a spine, and not serrate (shared with G. nanonocticolus); pectoral-fin spine stout, serrate along posterior margin (shared with G. stroudi); and a terminal mouth (vs. subterminal in G. nanonocticolus and G. stroudi). New taxon: Gelanoglanis travieso Rengifo and Lujan

Comparison of fish assemblages in two littoral habitats in a Neotropical morichal stream in Venezuela

Morichales are lowland streams in South American savannas with riparian forest dominated by the moriche palm (Mauritia flexuosa). We sampled littoral habitats from ten flooded vegetated patches (dominated by Mauritiella aculeate) and six sand banks in two months of the dry season (Feb-Mar 2005) in a stream in the savannas of Apure State, Venezuela. We collected samples that compromised 12,407 individual fishes of 107 species. Small-bodied fishes (< 100 mm), representing diverse trophic and life history strategies, were abundant. The most abundant species were in the families Characidae and Cichlidae. Fish assemblages from flooded vegetated patches differed significantly from those on adjacent sand banks. High structural complexity along vegetated shoreline habitats of morichal streams likely contributes to species richness and affects assemblage composition.

A new species of Hyphessobrycon (Characiformes, Characidae) from the upper Guaviare River, Orinoco River Basin, Colombia

Abstract Hyphessobrycon klausanni sp. n. is described from small drainages of the upper Guaviare River (Orinoco River Basin) in Colombia. It differs from all congeners by having a wide, conspicuous, dark lateral stripe extending from the anterior margin of the eye across the body and continued through the middle caudal-fin rays, and that covers (vertically) three or four horizontal scale rows. It also differs by having an orange-yellow stripe extending from the anterosuperior margin of the eye to the caudal peduncle above the lateral line in life. It differs from all other species of Hyphessobrycon that have a similar dark lateral stripe: H. cyanotaenia, H. loretoensis, H. melanostichos, H. nigricinctus, H. herbertaxelrodi, H. eschwartzae, H. montogoi, H. psittacus, H. metae, H. margitae, H. vanzolinii, and H. peruvianus in having only three or four pored scales in the lateral line, 21 to 24 lateral scales and six teeth in the inner premaxillary row. Hyphessobrycon klausanni differs from H. loretoensis in having seven to eight maxillary teeth (vs. three to four) and in having a longer caudal peduncle (12.4–17.0% SL vs. 4.6–8.0% SL). Additionally Hyphessobrycon klausanni can be distinguished from the other species of Hyphessobrycon with a dark lateral stripe from the Orinoco River Basin (H. metae and H. acaciae) in having two teeth in the outer premaxillary row (vs. three to four) and 10 branched pectoral–fin rays (vs. 11 to 12). It further differs from H. metae by the length of the snout (17.6–22.8% HL vs. 9.9–15.2% HL) and by the length of the caudal peduncle (12.4–17.0% SL vs. 7.3–11.8% SL).

Description of a New, Narrowly Endemic South American Darter (Characiformes: Crenuchidae) from the Central Guiana Shield Highlands of Guyana

Characidium amaila, new species, is described from rapids of the upper Kuribrong River (Potaro–Essequibo drainage) upstream of Amaila Falls. It is diagnosed from most other species of Characidium by lacking scales on the isthmus and chest, and by having 8–13 premaxillary teeth, the first four pectoral-fin rays noticeably thickened, 34–36 lateral line scales, and branchiostegal membranes that are free from each other across the isthmus. Characidium amaila is further distinguished by its large adult body size (max.  =  85.5 mm SL), and by having a tan body base color with a dark midlateral stripe that originates on the upper lip and continues posteriorly to the base of the middle caudal-fin rays, a gray to dark-black dorsum with two horizontal rows of small light spots formed by aligned light-colored scale centers, a dark humeral spot, up to 15 irregular black bars that extend from dorsum to lower sides, a light opercular margin, and fins that are uniformly dusky. Several cranial, vertebral, and swim bladder characteristics also support distinctiveness of the new species. Characidium amaila es descrita de los rápidos de el alto río Kuribrong (cuenca del Potaro–Essequibo) aguas arriba de las Cascadas de Amaila. Se distingue de la mayoría de las otras especies de Characidium por la ausencia de escamas en el istmo y el pecho, y por tener 8–13 dientes premaxilares, por poseer los primeros cuatro radios de la aleta pectoral notablemente ensanchados, 34–36 escamas en la línea lateral, y por tener las membranas de los radios branquiostegales separadas del istmo. Characidium amaila se distingue además por el gran tamaño del adulto (max.  =  85.5 mm SL) y por tener el cuerpo de color base café claro con una banda medio lateral que se origina en el labio superior y continúa posteriormente hasta la base de los radios medios de la aleta caudal; el dorso gris a negro con dos hileras horizontales de pequeños puntos claros formados por la alineación de los centros más claros de las escamas; una mancha humeral oscura; hasta quince barras negras irregulares que se extienden del dorso a la parte inferior de los flancos; el margen del opérculo de color más claro y aletas uniformemente grisáceas. Varios caracteres craneales, de las vertebras y de la vejiga natatoria apoyan el diagnostico de esta especie nueva.

Piabucina pleurotaenia Regan, a Synonym of P. erythrinoides Valenciennes (Pisces: Lebiasinidae); Its Distribution, Diet and Habitat in Lake Maracaibo Basin, Venezuela

Based on meristic, morphometric, coloration and distributional data, arguments are presented to support placing Piabucina pleurotaenia in the synonomy of P. erythrinoides (the volador). The volador inhabits most of the clear upland streams of the Maracaibo Basin where it feeds primarily on insects, fish and some vegetable matter. Sexual dimorphism in body and fin size is pronounced, and males have a peculiar modification of the scales above the anal fin. The sensory pore system is well developed in this species. All Maracaibo Basin specimens have an adipose dorsal fin.