The genus Erythrinus belongs to the family Erythrinidae, a neotropical fish group. This genus contains only two described species, Erythrinus erythrinus being the most widely distributed in South America. Six samples of this species from five distinct Brazilian localities and one from Argentina were studied cytogenetically. Four groups were identified on the basis of their chromosomal features. Group A comprises three samples, all with 2n ¼ 54 chromosomes, a very similar karyotypic structure, and the absence of chromosome differentiation between males and females. One sample bears up to four supernumerary microchromosomes, which look like 'double minute chromosomes' in appearance. Groups B-D comprise the three remaining samples, all sharing an X 1 X 1 X 2 X 2 /X 1 X 2 Y sex chromosome system. Group B shows 2n ¼ 54/53 chromosomes in females and males, respectively, and also shows up to three supernumerary microchromosomes. Groups C and D show 2n ¼ 52/51 chromosomes in females and males, respectively, but differ in the number of metacentric, subtelocentric, and acrocentric chromosomes. In these three groups (B-D), the Y is a metacentric chromosome clearly identified as the largest in the complement. The present results offer clear evidence that local samples of E. erythrinus retain exclusive and fixed chromosomal features, indicating that this species may represent a species complex.

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Summary Several cases of B chromosomes have been described for neotropical fish species. In some fish groups, this occurrence is sporadic, whereas in others it is more frequent. A high frequency of a metacentric macrochromosome B has been reported for Astyanax scabripinnis populations from different locations. In the present study, this kind of chromosome is reported for the first time in 2 other species of the same genus, A. fasciatus and A. schubarti. This coincidence, as well as the differential B chromosome frequency among the 3 Astyanax species, permit some considerations about its probable common origin and further distribution in this fish group.

This work aims to establish baseline frequencies of micronuclei (MN) and nuclear abnormalities (NA) in native fish species collected in situ from the Paraná River. For this purpose, the micronucleus test was applied in peripheral blood erythrocytes from specimens obtained from samplings collected at two localities (Posadas and Candelaria, Misiones, Argentina) during the period 2007-2010. The results were statistically analyzed using the Kruskal Wallis test. Data from nine fish species were obtained, among which Steindachnerina brevipinna (Characiformes) revealed the highest baseline frequency of MN and NA, showing statistically significant differences with regard to the other analyzed species. These results are the first report of baseline MN and NA frequencies for native fish species studied and could be useful for future comparisons with data of fishes belonging to other environments.Keywords: biomonitoring, micronuclei, nuclear abnormalities, fishes, Paraná River. Frequências basais de micronúcleos e anormalidades nucleares

Summary Among the Perciformes, Cichlidae represent the more specious group, geographically distributed in Africa, Asia and America. In the present work, 7 species of 5 genera of cichlids from the Paraná River (Misiones, Argentina) were cytogenetically characterized and discussed some aspects of the chromosome evolution. The following chromosome numbers and formulaes: were found for each analyzed species: Crenicichla niederleinii 2nϭ48 ( In B. vittata the microchromosomes are not heterochromatic and the 5th pair shows short arms entirely stained and, in coincidence, the AgNORs appears located at the same region. The results obtained evidence a wide chromosomal variation, either in number and structure that could be integrated with morphological and molecular data in phylogenetic studies.