The freshwater fish genus Astyanax is one of the most diverse among the Characidae. The genus is defined by a combination of character states that are widely distributed in Characidae. In addition, the genus has the broadest geographical distribution in the family, being found in a great variety of environments of the Neotropical region. Although phylogenetic relationships were treated only partially, many authors agree that the genus is not monophyletic. In this contribution, we study the phylogenetic relationships of Astyanax in the context of the family Characidae, by combining morphological and molecular data. A total of 520 morphological characters, nine molecular markers and 608 taxa are analysed, of which 98 belong to Astyanax. According to our results, Astyanax is not monophyletic. We recovered species attributed to Astyanax in different subfamilies: Gymnocharacinae (including the type species), Stevardiinae and Tetragonopterinae. Among the species recovered in Gymnocharacinae, most (including the type species, the resurrected Psalidodon, and the new genus Andromakhe gen. nov.) were recovered in Gymnocharacini, while the remaining ones were recovered in Probolodini (transferred to Deuterodon or the new genus Makunaima gen. nov.).

A new species assigned to the genus Trichomycterus from the area of the waterfalls of Tabay stream, Paraná River basin, Misiones, Argentina, is described. Trichomycterus ytororo sp. nov. is distinguished from all other species in the genus by the presence of 31–35 dorsal procurrent caudal-fin rays and the combination of some external characters such as: coloration, number of pectoral–fin rays and pores of the laterosensory canals. The new taxon belongs to a presumably monophyletic group of species composed of T. crassicaudatus, T. igobi, and T. stawiarski based on the presence of 24 or more thickly ossified and rigid procurrent caudal-fin rays with a slender distal tip extending along the tips of at least ten neural spines.

In this paper we describe Heptapterus mandimbusu sp. n., a new species of heptapterid catfish from a small tributary of the Uruguay River Basin in Misiones-Argentina. This new species is distinguished from all other congeners by the unique coloration pattern with aggregated melanophores scattered on dorsal and lateral surface of body, forming conspicuous size-variable blotches, and the combination of a long interdorsal distance (13.8–18.9 % SL), 14–18 anal-fin rays, short maxillary barbels (52.2–74.5 % HL), and the adipose fin confluent with caudal fin.

Freshwater sulfide springs have extreme environmental conditions that only few vertebrate species can tolerate. These species often develop a series of morphological and molecular adaptations to cope with the challenges of life under the toxic and hypoxic conditions of sulfide springs. In this paper, we described a new fish species of the genus Jenynsia , Anablepidae, from a sulfide spring in Northwestern Argentina, the first in the family known from such extreme environment. Jenynsia sulfurica n. sp. is diagnosable by the lack of scales on the pre-pelvic area or the presence of a single row of scales, continuous or not, from the isthmus to the bases of the pelvic fins. Additionally, it presents a series of morphological and molecular characteristics that appear convergent with those seen in other fish species (e.g., Poeciliids) inhabiting sulfide springs. Most notably, J . sulfurica has an enlarged head and postorbital area compared to other fish of the genus and a prognathous lower jaw with a hypertrophied lip, thought to facilitate respiration at the air-water interface. Analyses of cox1 sequence showed that J . sulfurica has two unique mutations resulting in amino acid substitutions convergent to those seen in Poeciliids from sulfide springs and known to provide a physiological mechanism related to living in sulfide environments. A phylogenetic analysis, including molecular and morphological characters, placed J . sulfurica as sister taxa to J . alternimaculata , a species found in nearby, non-sulfide habitats directly connected to the sulfide springs. Thus, it can be inferred that the selection imposed by the presence of H 2 S has resulted in the divergence between these two species and has potentially served as a barrier to gene flow.

Austrolebias wichi, new species, is herein described from seasonal ponds of the Bermejo river basin in the Western Chacoan district in northwestern Argentina. This species was found in a single pond, a paleochannel of the Bermejo River, which is seriously disturbed by soybean plantations surrounding it. Despite intensive sampling in the area, this species was only registered in this pond where it was relatively scarce. Therefore, we consider this species as critically endangered. This species is the sister species of A. patriciae in our phylogenetic analyses and is similar, in a general external aspect, to A. varzeae and A. carvalhoi. It can be distinguished among the species of Austrolebias by its unique color pattern in males. Additionally, from A. varzeae by presenting a supraorbital band equal or longer than the infraorbital band (vs. shorter) and from A. patriciae by the convex dorsal profile of head (vs. concave). Further diagnostic characters and additional comments on its ecology and reproduction are provided.

We present a new record for Austrolebias elongatus from Gualeguaychú, in Entre Ríos province, Argentina, based on new fieldwork and a revision of material deposited in national ichthyological collections. We also give evidence on the erroneous records of Austrolebias monstrosus and A. vandenbergi from Ituzaingó, Corrientes province, as well as present additional records from Salta province for those species. Material previously determined as A. elongatus from Santiago del Estero is attributed to A. monstrosus. We restrict the distribution of these two species to Semi-arid Chaco Region in Argentina, Paraguay and Bolivia.

El propósito de este trabajo es caracterizar y describir, desde una perspectiva crítica, la “Grounded Theory” como estrategia y metodología en la construcción de teorías a partir de redes o constructos conceptuales. Además, presentar lineamientos teórico-conceptuales, principios y procesos para desarrollar investigaciones de corte cualitativo mediante la aplicabilidad del método comparativo constante sustentado por Glaser y Strauss (1967), cuyo principio es arribar a teorizaciones relacionadas a partir de la realidad observada, tomando como punto de partida, el mundo fenomenológico de los protagonistas. Se muestra un enfoque metodológico que involucra tareas en el análisis de datos cualitativos como la codificación, categorización y procesos de teorización apoyados en el software ATLAS.ti. Finalmente, se expone un estudio de caso relacionado con la Caracterización de la Gestión de la Calidad Académico-Gerencial de Docentes que desempeñan funciones de dirección de Posgrado de la universidad ecuatoriana; que se apoyó en una investigación cualitativa de carácter emergente.

Specimens of Imparfinis were recently collected in north-western Argentina from the Bermejo River basin (Salta and Jujuy Provinces), del Valle River (Salta Province) and Horcones River (Santiago del Estero Province). An integrative approach to taxonomy, combining a detailed morphological study and molecular phylogenetic analyses, was applied to determine the species identity of these specimens. A principal components analysis of morphological data clustered the specimens from north-western Argentina and from the Amazon basin, indicating a close morphological resemblance. Also, a molecular phylogenetic analysis showed populations of I. guttatus from Argentina and Peru forming a clade. According to the conducted haplotype network analysis these populations are distinct in two mutations. Thus, in the absence of morphological or molecular data indicating the contrary, the combined method supports the identity of the specimens from the tributaries of the Paraguay River in Argentina as I. guttatus, whose type locality is in the upper Beni River basin in Bolivia. This contribution is also the first record for this species from Argentina. The disjunct distribution of I. guttatus provides new evidence reinforcing the hypothesis for the origin of the Paraguayan ichthyofauna. We also provide an approach to the phylogenetic relationships of Imparfinis in Heptapteridae.