Karyotypic similarities between two species of Rhamphichthys (Rhamphichthyidae, Gymnotiformes) from the Amazon basin

By

Silva, Patrícia
Nagamachi, Cleusa
Silva, Danillo
Milhomem, Susana
Cardoso, Adauto Lima
Oliveira, Jonas
Pieczarka, Julio

Type

Article

Date of Publication

2013

Original Publication

Comparative cytogenetics : international journal of plant & animal cytogenetics, karyosystematics and molecular systematics

Volume

7

Series / Issue

Issue: 4

Pages

279-291

Subjects

Cytogenetics , Fish , Gymnotiformes , Rhamphichthyidae

Contributed by

Pensoft Publishers

Language

English

Published by

St. Petersburg, Russia [Published] with technical support of Zoological Institute RAS [2007]-

Identifiers

DOI: https://doi.org/10.3897/compcytogen.v7i4.4366

 

Abstract

The family Rhamphichthyidae includes three genera: Rhamphichthys Müller et Troschel, 1846, Gymnorhamphichthys M. M. Ellis, 1912 and Iracema Triques, 1996. From this family, only the species Rhamphichthys hanni Meinken, 1937 has had its karyotype described. Here, we describe the karyotypes of two additional Rhamphichthys species: R. marmoratus Castelnau, 1855 from the Reserva de Desenvolvimento Sustentável Mamirauá, Amazonas state and R. prope rostratus Linnaeus, 1766 from Pará state, both in Brazil. Our karyotypic analyses demonstrated that the diploid number is conserved for the genus (2n = 50), but the karyotypic formulas (KFs) differed between R. marmoratus (44m/sm+6a) and R. prope rostratus (42m/sm+8a). In both species, the constitutive heterochromatin (CH) was located in the centromeric region of most chromosomes. Large heterochromatic blocks were found on the long arms of pairs 4 and 14 in R. marmoratus and on chromosomes 3, 4 and 19 in R. prope rostratus, which also has a heteromorphism in chromosome pair 1. The CH was DAPI positive, indicating that it is rich in AT base pairs. The Nucleolus Organizer Region (NOR) showed staining at a single location in both species: the long arm of pair 1 in R. marmoratus and the long arm of pair 12 in R. prope rostratus, where it showed a size heteromorphism. CMA3 staining coincided with that of Ag-NOR, indicating that the ribosomal genes contain interspaced GC-rich sequences. FISH with an 18S rDNA probe confirmed that there is only one NOR site in each species. These results can be used as potential cytogenetic markers for fish populations, and comparative analysis of the karyotypes of Hypopygus Hoedman, 1962, Rhamphichthys and Steatogenys Boulenger, 1898 suggests that the first two genera diverged later that the third.