Diversity of neotropical electric fish Microsternarchus (Teleostei: Gymnotiformes: Hypopomidae): an electrophysiological and geometric morphometric approach

The South American hypopomid electric fish tribe Microsternarchini includes three small species from the Upper Orinoco and Negro rivers. These are placed in monotypic genera: Microsternarchus, Racenisia and Procerusternarchus. Recent collections from tributaries in Negro, Solimões and Amazonas Basins have revealed new specimens of Microsternarchus with significant variations in external morphology and in Electric Organ Discharge parameters (EOD). In order to estimate the diversity within the genus a previous molecular study was done using DNA barcoding, that suggested the presence of multiple Microsternarchus's lineages with high levels of genetic divergence between them. Here we try to determine if the variation in morphology and EOD parameters in the new specimens meet the genetic divergence found. To test the presence of differences in shape among the different lineages we performed a geometric morphometric analysis, which included a relative warp and multivariate analysis on distances between 14 anatomical landmarks defined on the basis of external morphology and homologous among the lineages. The EOD variations were also explored using multivariate analyses of 20 electrophysiological parameters calculated through an algorithm developed in Matlab. The results show that there are significant differences in body shape and EOD in three lineages of Microsternarchus, and the features that contributed most were related to the shape of the head, the coefficient of variation of the signal and the duration and area of the different phases of the pulse. The discrimination of the three lineages confirms the occurrence of new species in the group that are currently being described

Two new species of Sternarchorhynchus Castelnau from the Amazon Basin, Brazil (Gymnotiformes: Apteronotidae)

Two new species of ghost knifefishes are described from the waterfalls and rapids of the Rio Mucajaí at the Cachoeira Paredão 2, Amazon basin in Roraima state, Brazil. Sternarchorhynchus severii, new species, is diagnosed from all congeners on the basis of body coloration, meristics and morphological characters such as white or yellow pigments along head and mid-dorsum forming long pale stripe, number of total anal-fin rays, and body proportion. Sternarchorhynchus caboclo, new species, is distinguished from the other species by the hyoid arch with four branchiostegal rays and the posttemporal not fused with the supracleithrum. © 2006 by Verlag Dr. Friedrich Pfeil

Procerusternarchus pixuna, a new genus and species of electric knifefish (Gymnotiformes: Hypopomidae, Microsternarchini) from the Negro river, South America

Procerusternarchus pixuna, a new genus and species of hypopomid gymnotiform, is described from several tributaries of Negro River, Amazonas State, Brazil. The new genus is included in the tribe Microsternarchini with the genera Microsternarchus and Racenisia based on a phylogenetic analysis of 41 anatomical, morphometric, meristic, and electric organ discharge variable characters. The new taxon is distinguished from Microsternarchus and Racenisia by the apomorphic presence of a deep, enlarged myogenic electric organ, an electric organ discharge with a greatly reduced negative phase and the plesiomorphic condition of a fully-scaled body, whereas scales are absent from the upper back of Microsternarchus and Racenisia

Parasitism by Clinostomum marginatum (Clinostomidae) in neotropical electric fish (Gymnotiformes) in the Brazilian Amazon

Gymnotiformes are currently recognized as electric fish, the vast majority of which emit low power electrical discharges. Clinostomum trematodes have been the subject of numerous investigations in several host species due to the ability of metacercariae of this genus to infect the muscles, fins and internal organs of fish. The present study aimed to record, for the first time, the occurrence of parasitism by Clinostomum marginatum in Gymnotiformes from the natural environments of two tributaries of the Amazon River in the Brazilian Amazon. Two specimens of Gymnotus coropinae, ten specimens of Brachyhypopomus brevirostris, two specimens of Gymnorhamphycthys petiti and one specimen of Microsternarchus bilineatus were captured. Infection with C. marginatum was identified in the form of 12 encysted metacercariae in the epidermis, with a prevalence of 0.1%, a mean infection intensity of 12/fish and an average abundance of 1.2. This is the first record of parasitism by the C. marginatum in South American Gymnotiformes of the B. brevirostris species

A new species of electric knifefish from the rio Negro, Amazon basin (Gymnotiformes: Hypopomidae, Microsternarchini)

A new species of electric knifefish of the genus Microsternarchus is described from the central basin of the rio Negro, Brazil. The new species is distinguished in external features from its single congener, Microsternarchus bilineatus, by the presence of a short caudal filament, a lower number of anal-fin rays, and uniform body pigmentation. Internally, features of the skeleton also distinguish the two species, in particular in the shape of the maxilla and antorbital