The original description of Mugil gaimardianus has created various taxonomic problems in the past since the description is ambiguous and the type specimen is apparently lost. The name M. gaimardianus could not be reliably applied to any known species and was suppressed by the International Commission on Zoological Nomenclature (ICZN) (Bulletin of Zoological Nomenclature, 51: 286–287, 1994). Nevertheless, karyological evidence has shown that there is a species of mullet in Venezuelan coastal waters that does not conform to the description of any other mullet from the Western Central Atlantic and has the feature of a red eye that was often used by earlier authors to define nominal M. gaimardianus. The purpose of this study was to make a morphological description of these unusual specimens, provide a morphological diagnosis from other species of Mugil present in the Caribbean and Western Central Atlantic and establish a valid name for the species.

This paper describes the karyotype analysis of Haemulon aurolineatum, Haemulon bonariensis and Haemulon plumierii, by Giemsa staining, C-banding, Ag-staining and fluorescent in situ hybridization (FISH), to locate the 18S and 5S rRNA genes. Diploid modal count in the three species was 2n = 48 acrocentric elements. Except for pair 24, which exhibited an unmistakable secondary constriction in all three species, it was not possible to classify them as homologous to each other because differences in chromosome size were too slight between adjacent pairs within a size-graded series. Ag-NOR clusters were located in pair 24 in the three species with signal located on the secondary constriction of these chromosomes. C-banding demonstrated that the three species share the same distribution pattern of the constitutive heterochromatin with centromeric heterochromatic blocks in the 23 chromosome pairs and a pericentromeric block in pair 24 which is coincident with the NORs. FISH experiments showed that 18S rDNA sequences were located coincident with the Ag-NOR site in the three species; however, differences in both the number and chromosome distribution of 5S-rDNA cluster were detected among them. Our data suggest that chromosome evolution of Haemulon has been preserved from major changes in the karyotypic macrostructure, whereas microstructural changes have occurred.

Karyotypes of three species of toadfish (Amphichthys cryptocentrus, Batrachoides manglae and Thalassophryne maculosa), reported here for the first time revealed diploid complements of 46 chromosomes. Karyo-evolutionary trend of these species is discussed. Based on differences in arm number, we suggest that T. maculosa possesses the most evolved karyotype among the three species, hence it would be the more recent one, followed by B. manglae and A. cryptocentrus.

Abstract.A cytogenetic analysis by conventional Giemsa staining, silver staining, C-banding, and fl uorescence in situ hybridization (FISH) was carried out on Brycon amazonicus from Caicara del Orinoco, Venezuela. The karyotype of this species is characterized by the presence of 2n = 50 chromosomes, a karyotypic formula 22m+14sm+14st, and a fundamental number of 100 chromosomal arms. Nucleolar organizer regions (NORs) and 18S rDNA genes are located in the terminal regions of the long arms of the second pair of subtelocentric chromosomes, corresponding to pair 13. C-banding revealed heterochromatin distribution in only seven chromosome pairs. The largest metacentric pair (number 1) possesses a paracentromeric block equilocally distributed in both chromosome arms, whereas in pairs 12 to 17 positive C band blocks were located in the paracentromeric region of the long arm, close to the centromere. Analysis performed with 5S rDNA gene revealed a terminal site located on the short arm of one small submetacentric chromosome (pair 15) corroborating previous studies with this repetitive gene showing an apparent conservation of 5S rDNA in the genome of these fi sh species. The data obtained in this study reinforce the chromosomal conservativeness in the species of the genus Brycon, related not only to the macro-chromosomal structure (diploid number, karyotypic formula, and fundamental number), but also to the repeated DNAs, such as heterochromatic regions and ribosomal DNAs. These data will contribute to a better understanding of chromosomal evolution in both Brycon and Characidae fi shes.