Apteronotus jurubidae (Fowler)

Carlos David de Santana & Javier A. Maldonado-Ocampo, 2004, Redescription of Apteronotus mariae (Eigenmann & Fisher, 1914) and the taxonomic status of Apteronotus jurubidae (Fowler, 1944) (Gymnotiformes: Apteronotidae)., Zootaxa 632, pp. 1-14 : 9-11

Additional information on Apteronotus jurubidae (Fowler)

Original description (Fowler, 1944: 242):

“Depth 64/5; head 62/5, width 24/5. Snout (in profile) 3 in head; eye 141/2, 4 in snout, 2 in interorbital, edges not free from skin of head; mouth extends back opposite front edge of eye, length from snout tip 3 in head; mouth rather narrow, width in front equals eye, closed mandible well included; nostril well separated, anterior in short tube and posterior midway in space to eye; interorbital 53/4 in head, convexly elevated; opercle with few striae. Gill opening 51/2 in head. Scales 88 in lateral line, continuous, with slender well exposed tubes. Scales on back and upper part of body large, all smaller on lower half of sides and on caudal peduncle extend over greater part of caudal, basally. Head and prepectoral region naked, and scales obsolete, small and embedded on upper hind part of head above opercle. Dorsal reduced to short simple posterior filament, its length 2 in head; very long anal with 167 branched rays, greatest fin height 21/4 in head, origin of fin well before gill opening; caudal peduncle slender, depth 83/5 in head; caudal 33/5, small, rounded behind; pectoral 11/2, rays 15. Color in alcohol largely dark uniform blackish brown. Anal posteriorly variegated with whitish, due to some irregular blackish blotches. Iris dark gray. Dorsal filament white basally, blackish terminally. Caudal largely black, irregularly white posteriorly. Pectoral black.”

In addition to traits described in the original description, the holotype of A. jurubidae (Fig. 4) exhibits the following features: lateral ethmoid ossified and slender, shaped as a tube. Dentary shape slender (longer than deep) (Fig. 5), with three irregular rows of teeth, 48 in total. Posterior limb of anguloarticular elongated. Mandibular canal unossified. Total precaudal vertebrae 17 (13 anterior plus 4 transitional vertebrae); maxilla rhomboid in lateral view; anterior surface of mesethmoid concave and lateral process of ventral ethmoid robust. The species is assigned to Apteronotinae (Albert & Campos-da-Paz, 1998; Albert, 2001) and in the genus Apteronotus as defined by Albert (2001). Apteronotus jurubidae is known only from the Rio Jurubidá, Pacific Slope, Colombia.

Using the information herein and by de Santana (2002; 2003), it is possible to distinguish A. jurubidae from A. mariae by the following traits: body coloration uniformly brown vs. light brown with small black spots distributed over the integument; dorsal region with uniform coloration vs. clear band from the preorbital region to the beginning of dorsal mid-sagittal electroreceptor organ in A. mariae .

Comments on endemism in the Rio Magdalena basin. A detailed phylogenetic analysis of Apteronotus is beyond the scope of the present paper and we herein confined ourselves to discuss the relationships of the two species with the apteronotids from the Trans-Andean region based on a preliminary hypothesis offered by de Santana (2002). That analysis was based on 97 morphological characters from 32 apteronotids taxa, with two species of Sternopygidae used as outgroups. Apteronotus mariae has an apomorphic character among the Trans-Andean apteronotids, the finely spotted coloration on the body. The presence of one or two clear bands in adults of A. mariae is a polymorphic feature. However, the presence of those bands could have at least two different patterns in the Trans-Andean apteronotids: (1) two clear bands present in juveniles and one clear band present in adults (e.g., Apteronotus cuchillo ); and (2) one clear band present throughout development (e.g., Apteronotus rostratus ). Some relevant characters used to identify and to infer the relationships in ghost knifefishes (above 100 mm TL) from the Trans-Andean region are summarized in Table 2. However, these character states can represent homoplasies instead of synapomorphies in apteronotids, or even in gymnotiforms (e.g., Alves-Gomes, 1998). A phylogenetic analysis on the relationships of the Trans-Andean ghost knifefishes, using molecular data is in preparation by the authors.

The presence of A. eschmeyeri , A. mariae , A. magdalenensis , and three other endemic gymnotiforms, Eigenmannia humboldtii , Sternopygus aequilabiatus and an undescribed species of Gymnotus (Maldonado-Ocampo & Albert, 2003), supports the previous hypotheses of the Rio Magdalena Basin as a region of endemism (e.g., Vari, 1988). As in the other basins from the eastern slope of the Cordilleras (e.g., the Amazon Basin), Apteronotidae is the dominant component of the gymnotiform fauna in the Rio Magdalena Basin. Of the 46 species currently recognized as valid in Apteronotidae (Albert, 2003; de Santana, 2003; de Santana et al., 2004), eight species are endemic to the Trans-Andean region, representing 17% of the total Apteronotidae diversity. The final uplift of the Andean Cordilleras in the Late Miocene (Hoorn et al., 1995) probably played a significant role in developing the local apteronotid Trans-Andean species diversity.