Hoplias malabaricus, a widely distributed neotropical fish (Central America to Argentina), may represent a group of distinct species showing diversified cytotypes with respect to chromosome number, morphology and sex systems. One of these karyotypic forms is characterized by an X1X1X2X2/X1X2Y sex chromosome system, with 2n = 40 and 39 chromosomes in females and males respectively. Analyses with G-, C- and chromosome replication banding permitted a better characterization of the sex chromosomes in this cytotype. The Y chromosome, unique in males, resulted from a translocation event between two biarmed chromosomes: one similar to chromosome 6 (X1) and the other one similar to chromosome 20 (X2), the latter corresponding to a probable identification. On the basis of the observed banding patterns, the Y chromosome may represent a stable dicentric, with an inactive centromere interstitially located on its long arm. The results are also related to a specific satellite DNA subfamily, previously characterized in Hoplias malabaricus, which appears to be associated with the X1 chromosome.

No abstract

No abstract

No abstract

No abstract

The chromosomes of the two species of needlefish, Potamorraphis cf. eigenmanni and Strongylura microps, from fresh waters of Argentina were analyzed using C-banding and silver staining and their karyotypes were described for the first time. The former species possessed 2n -54 and karyotype composed of three pairs metacentric to submetacentric chromosomes and 24 pairs of subtelo to telocentric chromosomes. The NORs were situated on the end of the shorter arms of one middle-sized bi-armed pair of chromosomes. The later species possessed 2n=50 and karyotype composed exclusively of subtelo to telocentric chromosomes gradually decreasing in size. The NORs were situated interstitially on the third pair of chromosomes. One or two supernumerary chromosomes were observed in one individual of the sample. Present data indicate greater cytotaxonomic diversity among species of needlefish which might be associated with their colonization of fresh waters.

The haploid DNA content and karyotypes of eight species of Blennius are studied. Six species had 2n = 48, two had 2n = 46.The karyotypes of these species have been compared with those of related species of the genus and it was suggested that pericentric inversions played an important role in the evolution of their karyotypes. No sex chromosomes were morphologically identifiable in these gonochorist species. The data are discussed in connection with possible lines of evolution within the genus.

No abstract