Supernumerary chromosomes were described for five species of Neotropical characiform fishes. These extra chromosomes were small, acrocentric and fully heterochromatic in Leporinus friderici from two different localities as well as in Leporinus sp., but metacentric and fully heterochromatic in Cyphocharax modesta and Prochilodus nigricans. In Characidium cf. zebra, this element was small, acrocentric and euchromatic. GC-rich DNA blocks were observed in the supernumerary chromosome of Leporinus sp. using chromomycin A 3 . The widespread occurrence of these extra chromosomal elements suggests their independent origins.

Four populations of Ancistrus cf. dubius (Loricariidae, Ancistrinae) were analyzed cytogenetically. They were from different rivers and creeks of the Pantanal Basin, in the state of Mato Grosso, Brazil. The populations were from four distinct locations: population A (4F and 8M), Coxip6 river, in the county of Chapada dos Guimaraes; population B (4F and 11M), Pari Creek, in the county of Cuiabii; population C (18F and 24M), Flechas Creek, the county of Caceres and population D (15F and 7M), Fundo Creek, in the county of Pocone. The modal diploid number is 2n=42 chromosomes (24M, lOSM and 8ST) and FN=84. Band C shows a system of sexual chromosomes XX/XY in populations B, C and D. The Ag-RONs are simple, with markers on pair 16 of the specimens analyzed. Sexual chromosomes aren't rare in fishes butAncistrus shows the unique case of two systems of sexual chromosomes, ZZ/ZW and XX/XY, in the specie identified as Ancistrus cf. dubius, and specimens of population A has no differentiation of the macro and micro chromosomatic structure between males and females. This suggests an alopatric speciation event of Ancistrus cf. dubius and a complex of species thus contributing to the understanding of citotaxonomic-evolutive relations in the Ancistrinae.

Cytogenetic and FISH analyses were performed in 30 Ancistrus cuiabae specimens from a bay near the town of Poconé, in the Pantanal of Mato Grosso, Brazil. The observed diploid number was 2n = 34 chromosomes for both sexes and three distinct katyotypic formulae were found, namely cytotype A (20m, 8sm, 6st, Fundamental Number/FN = 68; 6 males and 11 females), cytotype B (19m, 8sm, 6st, 1a, FN = 67; 8 males and 4 females) and cytotype C (18m, 8sm, 6st, 2a, FN = 66; a single male). NORs's analyses showed that these regions were located in distinct sites on the NOR-bearing chromosome pair, according to cytotypes. Thus, in cytotype A, NORs were located in the terminal region of the short arm of the second metacentric chromosome pair; in cytotype B, they were detected in the short arm of the metacentric chromosome and interstitially on the acrocentric chromosome and, in cytotype C, NORs were observed in the interstitial region of the acrocentric chromosome pair. C-positive heterochromatic bands were adjacent to the rDNA sites in the corresponding chromosomes. Thus, the chromosomal polymorphism of A. cuiabae was probably originated through a pericentric inversion in chromosome pair nº 2 involving the NOR sites, which represents a novelty in the Ancistrini tribe. The results also broaden the knowledge of the chromosomal evolution in Ancistrus, the most derived genus of the Ancistrini tribe.Foram analisados, com técnicas convencionais de citogenética e FISH, 30 exemplares da espécie Ancistrus cuiabae da baía Arrombado, próximo a Poconé, Pantanal do Mato Grosso. Foram observadas metáfases com número diploide 2n = 34 cromossomos para ambos os sexos e três fórmulas cariotípicas distintas, aqui denominadas de citótipo A, verificado em 06 machos e 11 fêmeas (20m, 8sm, 6st, Número Fundamental, NF = 68); citótipo B, em 08 machos e 04 fêmeas (19m, 8sm, 6st, 1a, NF = 67) e citótipo C em apenas 01 macho (18m, 8sm, 6st, 2a, NF = 66). As NORs confirmaram os distintos citótipos verificados, além de evidenciar que os cromossomos portadores de rDNA são os que representam o polimorfismo na espécie Ancistrus cuiabae. No citótipo A, as NORs foram verificadas na região terminal do braço curto do segundo par de cromossomos metacêntricos; no citótipo B, foram evidenciadas no segundo par, heteromórfico, no braço curto do cromossomo metacêntrico e intersticial no seu homólogo acrocêntrico; no citótipo C as NORs foram observadas na região intersticial num par de cromossomos acrocêntricos. A análise da heterocromatina constitutiva evidenciou blocos discretos adjacentes ao rDNA no segundo par de cromossomos de ambos os citótipos. Uma provável inversão pericêntrica é a hipótese proposta para a origem deste polimorfismo na espécie Ancistrus cuiabae. Estes resultados ampliam o conhecimento sobre o gênero Ancistrus, o mais derivado da tribo, contribuem para o conhecimento sobre este grupo de peixes e para inferir sobre a evolução cromossômica dos Ancistrini.

The genus Trigona contains at least 31 species, but there have been few cytogenetic studies of this group. In this work, four species of Trigona (T. branneri, T. chanchamayoensis, T. hyalinata, and T. recursa) from the municipality of Cuiabá, in the State of Mato Grosso, Brazil, were studied. In all of the species, the females had 2n = 34 chromosomes and the males had n = 17. The C-banding patterns showed that the karyotypes of these species consisted mainly of acrocentric and pseudoacrocentric chromosomes. These cytogenetic findings should useful in future phylogenetic studies of this group.

Hyphessobrycon rutiliflavidus, new species, is described from the upper rio Paraguai in Cuiab<, State of Mato Grosso, Brazil. The new species differs from all other congeners by the following combination of characters: black humeral spot, slightly diffuse at its tips, and caudal-peduncle blotch present; midlateral body stripe conspicuous in its posteriormost portion, extending to the tips of the middle caudal rays; anal fin with iii,15 to iv,19 rays (mode iv,17); upper jaw length, 42.3 to 49.5% of the head length; maxilla with 2–5 teeth (mode 3); all the fins of males reddish-orange and of females yellowish.