t 35 I ! Ichthyol. Explor. Freshwaters, Vol. 11, No.1, pp. 35-46, 6 figs., 1 tab., March 2000 I @ 2000 by Verlag Dr. Friedrich Pfeil, Miinchen, Germany - ISSN 0936-9902 A review of Venezuelan species of Hypophthalmus (Siluriformes: Pimelodidae) Heman Lopez-Femandez* and Kirk O. Winemiller* To date, only one (H. edentatus)of the three currently recognized species of the planktivorous catfishes of the genus Hypophthalmushas been identified in surveys from Venezuela and the Rio Orinoco Basin. Two additional species are now identified and the distributions of all three in Venezuela are mapped. Hypophthalmusedentatus is a more robust fish, with a shorter and wider head, and a triangular emarginate caudal fin. In comparison to H. edentatus,H. marginatusis more slender, with a longer head and forked caudal fin. Hypophthalmusd. fimbriatus is distinguished from its congeners by its more elongate body, darker body coloration, and long, flat, black inner mandibular barbels. Hypophthalmusedentatus and H. marginatus are sympatric in lowland rivers and floodplain habitats of the western llanos, mainstem Rio Orinoco, and Orinoco delta. In Venezuela, H. cf. fimbriatus is only known to occur in the black waters of the lower Rio Casiquiare where the other two species have never been collected. Hasta hoy, solo una (H. edentatus)de lag tres especiesreconocidas del genero de bagres planctivoros Hypophthal- mus ha sido seftalada para Venezuela y la cuenca del Rio Orinoco. Dos especies adicionales son identificadas; tambien se presenta un mapa de distribucion de lag tres especiesen Venezuela. Hypophthalmusedentatus es un pez robusto, con cabeza corta y ancha, y aleta caudal triangular y emarginada. En comparacion con H. edentatus, H. marginatus tiene el cuerpo mas fino, con la cabeza mas larga y la aleta caudal furcada. Hypophthalmuscf. fimbriatus se distingue de SUBcongeneres por su cuerpo mas alargado, coloracion corporal mas oscura y por lag barbas mandibulares intemas achatadasy de color negro. Hypophthalmusedentatus e H. marginatusson simpatricos en lag planicies y sabanasinundables de log llanos occidentales, el canal principal del Rio Orinoco y el delta del Orinoco. En Venezuela, H. d. fimbriatus solo se conoce de lag aguas negras del bajo Rio Casiquiare, donde lag otras dog especies nunca han sido colectadas. Introduction American paddlefish (Polyodon spathula), zoo- plankton are collected from the water column by The genus Hypophthalmus Cuvier contains three straining water over the fine seive created by currently recognized species of South American numerous long, thin gill rakers. Until recently, pimelodid catfishes (Carvalho & Goulding, 1985). the genus was assigned to the family Hypoph- Hypophthalmus are unusual among neotropical tha1midae based on Cuvier & Valenciennes' (1840: fishes in their habit of specialized plankton-feed- 224-225) interpretation of characters that deviate ing. In a manner similar to that used by North from the Pimelodidae (absence of teeth on the * Department of Wildlife and Fisheries Sciences,Texas A&M University, College Station, TX 77843,U.S.A. Ichthyol.Explor. Freshwaters, Vol. RNo. 1 36 mandible and palate and the large number of Methods branchiostegal rays). Based on more modern sys- tematic analyses, the current consensus is that All of the Hypophthalmus specimens availa- Hypophthalmusbelongs to the large neotropical ble in Venezuelan museums (MCNG, MBUCV, family Pimelodidae (Howes, 1983; Lundberg et MHNLS) were examined for comparison and al., 1991; de Pinna, 1993). taxonomic identification. Either all or a portion The genus Hypophthalmuscan be diagnosed of each lot was measured to compare morpholo- externally by the presence of scaleless skin and gy and determine diagnostic characters. Fin ray three pairs of barbels, one on the maxilla and two counts were made using transmitted light, and on the mandible, and small eyes located laterov- counts included every discernable ray. Measure- entrally in a position aproximately the mid-length ments were made with dial calipers to the near- of the head. The body is laterally compressed, est 0.1 mm when <130 mm, and with a metric bearing a long-based anal fin that runs from the tape to the nearest 1.0 mm when >130 mm. All anus to the anterior margin of the caudal pedun- measurements were taken as the straight-line cleoThe dorsal, pelvic, and pectoral fins have a distance between two points. Measurements were narrow base and lack spines. The posterior mar- taken as follows: Standard length (SL): from the gin of the caudal fin can be deeply forked or tip of the upper jaw to the middle of the base of emarginate depending on the species. caudal fin. Predorsal distance: from the tip of the Currently, Hypophthalmus has three recog- upper jaw to the most anterior point of the base nized species. Hypophthalmus edentatusSpix, in of dorsal fin. Prepelvic distance: from the tip of Spix & Agassiz, 1829, originally described from the upper jaw to the most anterior point of the Brazil, has been reported subsequently for the base of pelvic fin. Preanal distance: from the tip Peruvian Amazon (Cope, 1878), the Rio Parana of the upper jaw to the most anterior point of the (Nani & Fuster, 1947;Agostinho et al., 1997),the base of anal fin, without including the anus. Pre- Orinoco Basin in Venezuela (Mago, 1970) and pectoral distance: from the tip of the upper jaw to Colombia (Cala, 1986),and the La Plata Basin of the most anterior point of the base of pectoral fin. Argentina (Lopez et. al., 1980),thus being present Body depth: distance from the most anterior point in all the major cis-Andean basins of South Amer- of the base of dorsal fin, vertically to the line ica. Hypophthalmusmarginatus Valenciennes, 1840 where the anal fin rays insert into the body. Cau- was originally described from Surinam, and dal peduncle depth: depth vertically at the mid- according to Oliveira (1981)it could be present in point between the most posterior point of the the Rio Parana. However, Carvalho & Goulding base of anal fin and the most anterior point of the (1985) suggested that the species is restricted to insertion of caudal fin. Caudal peduncle length: the Amazon Basin. Hypophthalmus fimbriatus from the most posterior point of the base of anal Kner, 1857 apparently is restricted to the Rio fin to the most anterior point of the insertion of Negro in Brazil (Carvalho & Goulding, 1985). caudal fin. Head length (HL): from the tip of the Hypophthalmusedentatus is the only member upper jaw to most distal bony point of the oper- of the genus reported as present in the Orinoco cle, without including opercular membrane. Pec- Basin of Venezuela. The first published report of toral, pelvic, and dorsal fin length: from the most the genus in Venezuela appears to be that of anterior point of the base to the tip of the longest Mago (1970). Subsequent studies report H. eden- ray, following its direction. Anal fin length: from talus as inhabiting floodplains and whitewater the insertion of the rays to the tip of the longest caftos in some areas of the western and central ray, following its direction. Caudal fin length llanos (Taphorn & Lilyestrom, 1984;Lasso et. al., (dorsal lobe, ventral lobe, median rays): from the 1995;Rodriguez & Lewis, 1997).Recent captures middle point of the base to the tip of the longest of several Hypophthalmusspecimens with differ- ray of each lobe. Dorsal and anal fin base: from ent morphology than that of H. edentatusmoti- the most anterior to the most posterior point of vated our review of the genus in Venezuela. This the base of the fin. Dorsal to caudal distance: paper provides the first report of H. marginatus from the most anterior point of the base of the andH. cf. fimbriatus in Venezuela, a distribution dorsal to the mid-point of the base of the caudal. map for all three specieswithin the country, com- Eye to dorsal distance: from the most posterior parisons of morphological differences, and a key point of the orbit to the most anterior point of the for species identification. base of the dorsal fin. Maxillary, outer mandibu- Lopez-Fernandez& Winemiller: VenezuelanHypophthalmus 37 I lar, and inner mandibular barbels:the distance Hypophthalmusedentatus Spix r from the base to the tip of the extended barbel. (Fig. 1b) Snout length: from the tip of the upper jaw to the most anterior point of the orbit. Orbital diameter: Material examined. MCNG 30856, 3 ex., 245.0- horizontally from the most anterior to the most 267.0rom SL (1 measured); Anzoategui: Laguna posterior point of the orbit. Interorbital distance: EI Venado, beside Rio Orinoco, 8°10'N 63°38'W. dorsally between the most internal points of the -MCNG 19624,9ex., 127.3-185.0romSL (1 meas- orbits. Postorbital distance: from the most poste- ured); Apure: Rio Apure, Laguna Remanso, rior point of the orbit to the posterior end of the 7°54'N 67°23'W. - MCNG 37237, 3 ex., 334.0- opercle, without including opercular membrane. 364.0rom SL; Portuguesa:Canal Cocito, 8°56'O9"N Inter-nares distance anteriorly/posteriorly: the 68°59'15"W. - MHNLS 1463, 1 ex., 107.1 rom SL; distance between the anterior/posterior pair of Apure: Rio Apure, Mango Verde. - ANSP nares. Gill raker length: at the ceratobranchial, 165355.51,51 ex., 55.4-100.5rom SL (9 measured); from the base to the tip of the raker, following its Apure: San Fernando to Puerto Paez Highway, direction. 7°20'N 67°35'W. Museum abbreviations: ANSP, Academy of Natural Sciences,Philadelphia; MBUCV, Museo Diagnosis. Hypophthalmus edentatus is distin- de Biologia de la Universidad Central de Vene- guished from the other species in the genus by zuela, Caracas; MCNG, Museo de Ciencias Nat- the following combination of characters: caudal urales, Guanare; MHNLS, Museo de Historia fin emarginate, in constrast to deeply forked in Natural La Salle, Caracas.