Abstract
In the present work three fish species were analyzed: two belong to the Cheirodontinae
subfamily (Serrapinnus notomelas and Serrapinnus sp.1) and one to Aphyocharacinae
subfamily (Aphyocharax anisitsi), collected from basins of the Paraná river and Tietê
river. Four S. notomelas populations from the Araquá and Pântano rivers, Cascatinha
Stream and Paraná river, were studied. In this last also were the others species. The
analysis of the results showed a diploid number the 52 chromosomes for all the
analyzed populations in the Serrapinnus genus, however, interespecific differences in
the karyotypic formulae, were observed. S. notomelas showed 16M+22SM+10ST+4A,
with NF=100 for males and 16M+23SM+10ST+3A, with NF=101 for females.
Serrapinnus sp.1 showed 8M+16SM+4ST+24A, with NF=80 for males and
8M+15SM+4ST+25A, with NF=79 for females. The difference in the NF among the
sexes is due to presence of one heteromorphic pair (submetacentric/acrocentric) in the
females of the two species, characterizing a sexual chromosomal mechanism of the type
ZZ/ZW. This sexual heteromorphic chromosomes system showed to be different in
relation to the type of W chromosomes in the two species, while that in S. notomelas the
W is a submetacentric chromosomes in the Serrapinnus sp.1 is acrocentric. The C band
technique demonstrated a pericentromeric heterocromatin pattern with NOR region
positive C band in all the S. notomelas populations studied. Moreover, the presence of
interstitial C band in long arm of a submetacentric chromosomes pair, was observed. In
relation to the NORs, intraespecific differences also were found. While the system
simple AgNOR (pair 26) was detected for three of four S. notomelas populations
studied, to Serrapinnus sp.1 two chromosomal pairs were involved with this region.
The population from Paraná river showed intrapopulational variability and six diferent
NOR patterns were distinguished among 9 specimens. This can correspond the copies
transposition of rDNA citrons, fixed in the 26 pair (preferential NOR), for different
locality in the genome. This is corroborated by the fact of other populations showed
simple AgNOR, in the 26 pair. Although the mechanism of transposition by mobile
elements, are most probabily we not discard the hypothesis of occurrence of other
rearrangements types such as translocations, duplications, amplifications, amongst
others. Moreover, C band variation coincidence with patterns types different was
observed. Probability the heterocromatin that flank the rDNA genes of the 26 pair,
follow these genes independently of the mechanism involved in this variability.