Abstract
The order Anguilliformes comprises 15 families, 141 genera and 791 fish species. Eight families had at least one karyotyped species, with a prevalence of 2n = 38 chromosomes and high fundamental numbers (FN). The only exception to this pattern is the family Muraenidae, in which the eight species analyzed presented 2n = 42 chromosomes. Despite of the large number of Anguilliformes species, karyotypic reports are available for only a few representatives. In the present work, a species of Ophichthidae, Myrichthys ocellatus (2n = 38; 8m+14sm+10st+6a; FN = 70) and four species of Muraenidae, Enchelycore nigricans (2n = 42; 6m+8sm+12st+16a; FN = 68), Gymnothorax miliaris (2n = 42; 14m+18sm+10st; FN = 84), G. vicinus (2n = 42; 8m+6sm+28a; FN = 56) and Muraena pavonina (2n = 42; 6m+4sm+32a; FN = 52), collected along the Northeastern coast of Brazil and around the St Peter and St Paul Archipelago were analyzed. Typical large metacentric chromosomes were observed in all species. Conspicuous polymorphic heterochromatic regions were observed at the centromeres of most chromosomes and at single ribosomal sites. The data obtained for Ophichthidae corroborate the hypothesis of a karyotypic diversification mainly due to pericentric inversions and Robertsonian rearrangements, while the identification of constant chromosome numbers in Muraenidae (2n = 42) suggests a karyotype diversification through pericentric inversions and heterochromatin processes.
Highlights
Cytogenetic analyses in fish have allowed to determine sex chromosomes (Moreira-Filho et al, 1993; Devlin and Nagahama, 2002; Molina and Galetti, 2007), the characterization of vertebrate models, like the zebrafish (Sola and Gornung, 2001), the evaluation of genetically modified lineages (Porto-Foresti et al, 2004), and to perform inferences on cytotaxonomic (Bertollo et al, 2000; Bertollo et al, 2004) and evolutionary issues (Demirok and Ünlü, 2001), besides the detection of cryptic species (MoreiraFilho and Bertollo, 1991)
In this work we performed a cytogenetic analysis of Myrichthys ocellatus (Ophichthidae), Enchelycore nigricans, Gymnothorax vicinus, Gymnothorax miliaris and Muraena pavonina (Muraenidae) collected in the Brazilian coast and around Atlantic oceanic islands, using conventional staining, Ag-nucleolar organizer regions (NORs) and C-banding
A diploid number of 2n = 42 (FN = 56) and a karyotype formula with 8m+6sm+28a were observed in G. vicinus (Figures 3a, b)
Summary
Cytogenetic analyses in fish have allowed to determine sex chromosomes (Moreira-Filho et al, 1993; Devlin and Nagahama, 2002; Molina and Galetti, 2007), the characterization of vertebrate models, like the zebrafish (Sola and Gornung, 2001), the evaluation of genetically modified lineages (Porto-Foresti et al, 2004), and to perform inferences on cytotaxonomic (Bertollo et al, 2000; Bertollo et al, 2004) and evolutionary issues (Demirok and Ünlü, 2001), besides the detection of cryptic species (MoreiraFilho and Bertollo, 1991). Cytogenetic data are still restricted for some fish groups, such as Anguilliformes, which comprises 15 families, 141 genera and 791 species (Nelson, 2006) and are popularly known as eels, congers or morays. A remarkable heteromorphism was reported between the NOR-bearing homologues in several species (Cau et al, 1988), which in some cases led to the misidentification of this pair as sex chromosomes (Wiberg, 1983). They represent some of the most typical reef fish groups in the Atlantic Ocean, few cytogenetic studies have been carried out in Muraenidae and Ophichthidae. In this work we performed a cytogenetic analysis of Myrichthys ocellatus (Ophichthidae), Enchelycore nigricans, Gymnothorax vicinus, Gymnothorax miliaris and Muraena pavonina (Muraenidae) collected in the Brazilian coast and around Atlantic oceanic islands, using conventional staining, Ag-NOR and C-banding
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