Caracterização taxonômica das espécies de Eigenmannia (Gymnotiformes, Sternopygidae) da bacia do Rio Paraguai na região do Forte Coimbra, Mato Grosso do Sul

Abstract

One of the rising taxonomic groups of Neotropical fishes is the Gymnotiformes order that comprises the tuviras, sarapós, and ituís. For more than 300 years this group has called the attention of researchers due to its distinctive appearance and its specific physical capacity for electrical production and reception. The group has several morphological changes, such as the absence of pelvic and dorsal fins, the presence of an extremely elongated anal fin and the anus anteriorly located, below the head or pectoral fin region. The genus Eigenmannia (Sternopygidae) is characterized by a compressed and translucent body, short snout, relatively large eyes and frequently the presence of lateral stripes along the body. The objective of the present work is to taxonomically characterize the species of the genus Eigenmannia in the Paraguay river basin at the region of the Forte Coimbra, MS. The specimens were collected during an expedition to the region in 2017, during the dry season. The material was analyzed at the UFGD-FCBA Zoology Lab (Dourados - MS). Morphometric measurements were taken point-to-point using a digital caliper, under a stereomicroscope and 29 parameters were measured. Subsequently, meristic counts were performed, such as the number of anal and pectoral fin rays, and series scales above and below the lateral line. Finally, the data were compared with each other and with the literature data and the presence of two distinct morphological entities were identified: Eigenmannia cf. trilineata and Eigenmannia sp. Nov. The first morphotype fits into the definition of the E. trilineata species complex because it presents a color pattern composed of four dark longitudinal lines. Eigenmannia sp. nov can be diagnosed from all other congeners by the combination of the absence of longitudinal bands and the presence of a triangle-shaped concentration of melanophores in the operculum. Recognized morphotypes can be diagnosed with each other by the distinct color pattern, the short snout in Eigenmannia cf. trilineata (vs. elongated inEigenmannia sp), slightly oval distal margin of pectoral fin in Eigenmannia cf. trilineata (vs. straight margin in Eigenmannia sp. nov.) and upper maxillary margin passing through the vertical of the anterior nostril or between the anterior and posterior nostrils in Eigenmannia cf. trilineata (vs. vertical passing through the anterior margin of the posterior nostril). The results indicate that the Pantanal ichthyofauna, although relatively well-known, still needing additional taxonomic studies.