Gymnotus Linnaeus

James S. Albert & William G. R. Crampton, 2003, Seven new species of the Neotropical electric fish Gymnotus (Teleostei, Gymnotiformes) with a redescription of G. carapo (Linnaeus)., Zootaxa 287, pp. 1-54 : 2-4

[[ Genus Gymnotus Linnaeus ]]

The Neotropical electric fish genus Gymnotus (Linnaeus 1758) is substantially more diverse than was previously recognized. New methods of sampling, identifying, and collecting electric fishes have unveiled numerous species in previously unexplored habitats and regions (Crampton 1996a; Lundberg et al.1996; Crampton 1998; Albert & Crampton 2001). Further, the use of new techniques for characterizing morphology, electric organ discharges, and genetic differences have demonstrated that much of what was once regarded as intraspecific variation represents interspecific differences (Campos-da-Paz & Costa 1996; Fernandes-Matioli et al. 1998a; Fernandes-Matioli et al. 1998b; Albert et al. 1999; Fernandes-Matioli et al. 2000; Fernandes-Matioli et al. 2001; Albert & Crampton 2001; Fernandes-Matioli & Almeida-Toledo, 2001).

Gymnotus species are aggressive nocturnal predators of fishes and other small aquatic animals, and most are territorial. The males of at least two Gymnotus species build and guard nests of foam and/or aquatic vegetation (Crampton & Hopkins pers. obs.). The type species Gymnotus carapo is reported to mouth brood its eggs and larvae (Kirschbaum & Wieczorek 2002). Gymnotus is the most geographically widespread of all gymnotiforms, extending from the Río Salado in the Pampas of Argentina (36°S) to the Río San Nicolás of southeastern Chiapas, Mexico (18°N), and is present in the continental waters of all South and Middle American countries except Chile and Belize (Albert 2001). Prior to this report, 25 species names were available for Gymnotus , of which five were synonymized with the type species G. carapo (Mago-Leccia 1994), and one with G. coatesi (Campos da Paz 2000). The geographical ranges of the currently valid Gymnotus species are summarized in Table 1. Gymnotus exhibits its greatest diversity in the western portion of the Amazon basin where 10 species are currently recognized. Gymnotus anguillaris Hoedeman is recognized here as distinct from G. coropinae Hoedeman with which it has been synonymized (Nijssen & Isbrücker 1968). Data for and comparisons to G. coropinae will be presented in a forthcoming redescription of this species (Crampton & Albert unpubl. obs.).

Here we present evidence for the existence of seven new species of Gymnotus from examination of populations from throughout tropical South and Middle America. We describe these new taxa on the basis of unique color patterns and unique combinations of morphometric, meristic, and osteological features. We also redescribe the geographically widespread species G. carapo sensu stricto ( G. carapo s.s.) and distinguish six allopatric populations of G. carapo s.s. by differences in the mean and modal values of morphometric and meristic traits. The original description of G. carapo (Linnaeus, 1758) provides only enough information to identify specimens to the Order Gymnotiformes (sensu MagoLeccia, 1994). Subsequent diagnoses and keys (Ellis 1913; Hoedeman 1962; Mago-Leccia 1994; Albert & Miller 1995) did not provide sufficient information to differentiate G. carapo s.s. from other member of the G. carapo species-group.

The material basis of these descriptions is 781 museum lots of Gymnotus bearing more than 2700 specimens from 32 museums. This study is to our knowledge the most thorough alpha-level review of morphological variation in any gymnotiform genus to date. The existence of so many previously unrecognized and undescribed taxa within existing museum collections is due in part to the cryptic nature of phenotypic diversity in Gymnotus . These fishes possess few external visual cues for species recognition. The lack of appreciation for diversity in Gymnotus has been compounded by a lack of published accounts of intraspecific variation. We predict that similarly high levels of cryptic diversity may exist in other gymnotiform groups with geographic distributions well represented in museum collections (e.g., Brachyhypopomus ; Gymnorhamphichthys , Eigenmannia , Sternarchorhynchus ).