Karyotypic similarities between two species of Rhamphichthys (Rhamphichthyidae, Gymnotiformes) from the Amazon basin.
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: Rhamphichthys marmoratus Castelnau, 1855 from the Reserva de Desenvolvimento Sustentável Mamirauá, Amazonas state and Rhamphichthys 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 Rhamphichthys marmoratus (44m/sm+6a) and Rhamphichthys 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 Rhamphichthys marmoratus and on chromosomes 3, 4 and 19 in Rhamphichthys 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 Rhamphichthys marmoratus and the long arm of pair 12 in Rhamphichthys 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.
Universidade Federal do Pará, Instituto de Ciências Biológicas, Av Perimetral, SN. Guamá. 66075-900. Belém, Para, Brazil ; CNPq Mastership Scholarship in Genetics and Molecular Biology.
Patrícia Corrêa
PC
da Silva
Universidade Federal do Pará, Instituto de Ciências Biológicas, Av Perimetral, SN. Guamá. 66075-900. Belém, Para, Brazil ; CNPq Researcher, Belém, Brazi.
Cleusa Yoshiko
CY
Nagamachi
Universidade Federal do Pará, Instituto de Ciências Biológicas, Av Perimetral, SN. Guamá. 66075-900. Belém, Para, Brazil ; CNPq Doctorship Scholarship in Genetics and Molecular Biology.
Danillo Dos Santos
Ddos S
Silva
Universidade Federal do Pará, Instituto de Ciências Biológicas, Av Perimetral, SN. Guamá. 66075-900. Belém, Para, Brazil.
Susana Suely Rodrigues
SS
Milhomem
Universidade Federal do Pará, Instituto de Ciências Biológicas, Av Perimetral, SN. Guamá. 66075-900. Belém, Para, Brazil ; CNPq Undergraduated Scholarship.
Adauto Lima
AL
Cardoso
Instituto de Desenvolvimento Sustentável Mamirauá, Estrada do Bexiga, 2584 69470-000. Tefé, Amazonas, Brazil.
Jonas Alves
JA
de Oliveira
Universidade Federal do Pará, Instituto de Ciências Biológicas, Av Perimetral, SN. Guamá. 66075-900. Belém, Para, Brazil ; CNPq Researcher, Belém, Brazi.
Julio Cesar
JC
Pieczarka
Cytogenetics; FISH; Gymnotiformes; Rhamphichthyidae