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Acta zoológica lilloana 50 (1–2): 125–128, 2006 125 COMUNICACIÓN Populations of Characidium rachovii (Crenuchidae: Characidiinae) with reduction of the adipose fin from Argentina and a Southernmost record of C. occidentale Fernández, L. 1 2 1y A. M. Miquelarena 2 Fundación Miguel Lillo. Miguel Lillo 251, (4000) Tucumán, Argentina. E-mail: Esta dirección de correo electrónico está protegida contra los robots de spam, necesita tener Javascript activado para poder verla Departamento Científico Zoología Vertebrados, Ictiología, Museo de La Plata. Paseo del Bosque s/n, (1900) La Plata, Argentina. E-mail: Esta dirección de correo electrónico está protegida contra los robots de spam, necesita tener Javascript activado para poder verla Instituto de Limnología “Dr. Raúl A. Ringuelet”. CC 712, (1900) La Plata, Argentina. “Populations of Characidium rachovii (Crenuchidae: Characidiinae) with reduction of the adipose fin from Argentina and a Southernmost record of C. occidentale”. KEYWORDS: Characidium rachovii, Characidium occidentale, Characiformes, Southern South America, taxonomy, distribution. PALABRAS CLAV E: Characidium rachovii, Characidium occidentale, Characiformes, Sud América, taxonomía, distribución. The genus Characidium includes approximately 43 valid species that occur widely in major tropical and subtropical drainages between eastern Panamá and the vicinity of La Plata (Buenos Aires) (Ringuelet et al., 1978; Buckup et al., 2000; Buckup & Hahn, 2000; Souto de Melo & Buckup, 2002). Five species of Characidium have been reported for Argentina— Characidium borellii (Boulenger, 1895), C. fasciatum Reinhardt = C. cf. zebra, C. pterostictum Gómez, C. tenue (Cope), and C. rachovii Regan (Pozzi, 1935; Braga, 2000/ 2001; López et al., 2003; López & Miquelarena, 2005). The objective of this note is to report on populations of Characidium rachovii (Fig. 1, Table 1) with reduction and absence of the adipose fin from Salí-Dulce and Paraná River basins, Argentina. In addition, we make considerations about the use of this character as diagnostic at the alpha-level and mention the occurrence of Characidium occidentale Buckup & Reis in the Lower Uruguay River basin. C. occidentale (Table 1), was described by Buckup & Reis in 1997 for a tributary of the Uruguay River, in Brazil and we include the first report from the Chirimay Miní stream, a tributary of the Uruguay River in the Province of Misiones, Argentina. The material studied is deposited in the ichthyologic collections of the Fundación Miguel Lillo, Tucumán, Argentina (FML); Museo de La Plata, La Plata, Argentina (MLP) and Instituto de Limnología Dr. Raúl A. Ringuelet, Buenos Aires, Argentina (ILPLA). Material examined: Characidium rachovii: ILPLA 1582, 5 specimens (2 cleared and stained), 34.1-36.8 mm SL, Tucumán, Departamento Chicligasta, Gastona River, collectors L. Fernández and G. Scrocchi, Feb. 1999; FML 2554, 25 specimens, 32.9-40.1 mm SL, same data as above; FML 2593, 4 specimens, 28.1-45.9 mm SL, same data as above; MLP 7293, 27 specimens (8 specimens with vestigial adipose fin), 22.7-32.8 mm SL, Santa Fe, Madrejón near Colastiné River, collectors: R. Ringuelet and R. Arámburu, 1 Oct. 1961. Characidium occidentale: ILPLA 1581, 2 specimens, 40.3-41.8 mm SL, Misiones, Departamento Apóstoles, Chirimay Miní stream, Uruguay River basin, (27º54’S-55º45’W), collectors: R. Filiberto et al., 8 Jan. 2001. The measurements were taken on the left side of the specimen with a digital calliper with a precision of 0.02 mm under a stereomicroscope according to Buckup (1993). In northwestern Argentina, Characidium cf. zebra is mainly distributed in the 126 L. Fernández & A. M. Miquelarena: Populations of Characidium rachovii western mountain rivers of Tucumán, whereas C. rachovii occurs in the southern and eastern rivers of that province. Specimens of C. rachovii presenting reduced to absent adipose fin (Fig. 1) as well as specimens showing a normal adipose fin were collected at the same time in a canal that overflows from the Gastona River (Salí-Dulce basin). A vestigial adipose fin was also the observed condition in eight specimens of the same species from the Lower Paraná River (Santa Fe). All specimens of C. rachovii present 33 to 35 lateral line scales (11 perforated scales). A reduced adipose fin in a Characidium species has first been reported by Buckup & Hahn (2000), who diagnosed C. vestigipinne by the reduction of the adipose fin, which can be very small (less 4% SL) or absent. This species is endemic from the upper Uruguay basin and has been included in a monophyletic clade together with C. occidentale, C. orientale and C. rachovii based on four external characters. In addition to having a variably reduced adipose fin, C. vestigipinne A Standard length (mm) Total length (mm) Percentages of standard length Head length Prepectoral distance Predorsal distance Prepelvic distance Preanal distance Anal-apex distance Body width Body depth at dorsal origin Body depth at anal origin Body depth at caudal peduncle Percentages of head length Snout length Snout-maxilla tip Anterior nares-orbit Posterior nares-orbit Cheek depth Orbital diameter Interorbital distance 33.3 41.2 27.5 26.8 48.9 52.8 70.8 87.9 28.9 28.4 17.9 12.2 20.8 21.5 28.0 24.8 10.9 32.3 25.1 B 21.7 28.1 31.9 28.5 51.9 53.4 75.2 95.2 29.8 27.4 19.3 10.8 21.2 23.3 25.8 26.5 27.9 32.9 21.0 can be further distinguished from other species of the genus Characidium by the presence of a lateral line complete or beyond the 12th scale. The specimens examined for Argentinean localities shared the four synapomorphies for that clade following Buckup & Hahn (2000). Our findings show that the reduction or absence of the adipose fin might be a frequent condition among Characidium species. This has led us to question its use as an alpha-level diagnostic character. Though not yet quantified, we have observed that several species of small Characiformes can present variation in the degree of development of the adipose fin, such variation occurring only in some populations of the species (also Vari, pers. comm.). This appears to be the case we observed in the Characidiinae C. rachovii. Hence, we consider that the use of the character reduction or absence of the adipose fin in that group as diagnostic at the alpha-level should be avoided or clearly justified. We follow Buckup & Reis (1997) for the identifications of the C. occidentale C 36.5 45.9 26.5 27.2 50.1 52.1 72.1 88.3 29.7 29.7 19.7 12.7 23.6 26.8 10.8 23.9 28.2 29.1 22.9 D 35.0 43.7 26.9 25.9 48.3 52.1 72.3 89.2 28.6 28.4 19.0 12.0 20.2 23.9 29.1 22.7 26.9 30.3 23.6 E 40.3 51.6 25.8 27.3 47.9 51.6 72.7 91.6 12.1 27.0 18.4 12.6 27.3 25.0 29.7 24.7 10.4 32.8 25.0 F 41.8 53.0 28.2 28.2 48.1 51.4 76.2 95.2 12.4 26.3 18.8 11.9 24.6 23.6 12.1 23.7 10.5 32.0 23.5 Table 1. Morphometric data of Characidium rachovii (with adipose fin reduced and fin absent) FML 2593 (AD) and Characidium occidentale ILPLA 1581 (E-F). Acta zoológica lilloana 50 (1–2): 125–128, 2006 127 Figure 1. Characidum rachovii FML 2554, with adipose fin developed (above), FML 2593, with adipose fin reduced (center), and FML 2593, adipose fin absent (bottom). specimens: Dark spots on dorsal fin forming a continuous band across rays; anterior portion of anal fin of males with two conspicuous dark blotches, followed by smaller spots on the posterior portion; 12 series of scales around caudal peduncle; lateral line complete; 33- 34 lateral-line scales; scales above lateral line 5; scales below lateral line 5; scales in predorsal series 12. Dorsal-fin rays iii, 10. Anal-fin rays ii, 7. Pectoralfin rays iii, 6-7. Pelvic-fin rays i, 6, i. Branched caudal-fin rays 9 on dorsal lobe, 8 on ventral lobe. 128 L. Fernández & A. M. Miquelarena: Populations of Characidium rachovii We thank A. Aquino (AMNH), H. López (MLP) and R. Menni (MLP), for the critical reading of the manuscript. REFERENCES Braga, L. 2000/2001. Primer registro para Argentina de Characidium tenue y C. pterostictum (Characiformes, Crenuchidae). Physis, Secc. B, 58: 49-50. Buckup, P. A. 1993. Phylogenetic interrelationships and reductive evolution in neotropical characidiin fishes (Characiformes, Ostariophysi). Cladistics, 9: 305-341. Buckup, P. A. & Hahn, L. 2000. Characidium vestigipinne: A new species of Characidiinae (Teleostei, Characiformes) from Southern Brazil. Copeia, 2000: 150-155. Buckup, P. A. & Reis, R. 1997. Characidiin Genus Characidium (Teleostei, Characiformes) in Southern Brazil, with description of three new species. Copeia, 1997: 531-548. Buckup, P. A., Zamprogno, C., Vieira, F. & Teixeira, R. L. ( 2000). Waterfall climbing in Characidium (Crenuchidae: Characidiinae) from eastern Brazil. Ichthyol. Explor. Freshwaters, 4: 97-154. López, H. L. & Miquelarena, A. M. 2005. Biogeografía de los peces continentales de la Argentina, 509-550. En: Regionalización biogeográfica de Iberoamérica y tópicos afines: Primeras Jornadas Biogeográficas de la Red Iberoamericana de Biogeografía y Entomología Sistemática, J. Llorente Bousquets y Morrone, J.J. (eds.). RIBES XII-I-CYTED, México. ISBN-970-32-2509-8. López, H. L.; A. M. Miquelarena & R. C. Menni. 2003. Lista comentada de los peces continentales de la Argentina. ProBiota, FCNyM-UNLP, La Plata, Ser. Téc. y Didáctica nº 5: 1-85. ISSN 1515-9329. Pozzi, A. J. 1945. Sistemática y distribución de los peces de la República Argentina. GAEA, 7: 239-292. Ringuelet, R. A., Miquelarena, A. M. & Menni, R. C. 1978. Presencia en los alrededores de la Plata de Characidium (Jobertina) rachowi y de Hyphessobrycon meridionalis sp. nov. (Osteichthyes, Tetragonopteridae). Limnobios, 1: 242-257. Souto De Melo, M. R. & Buckup, P. A. 2002. Characidium stigmosum (Characiformes: Crenuchidae): a new species of characidiin fish from Central Brazil. Copeia, 2002: 988-993.