Fishes of the Loricariidae family, known as “cascudos”, constitute an endemic group in Neotropical freshwaters. In this study, were cytogenetically examined two species of Loricariidae (Pterygoplichthys anisitsi Eigenmann & Kennedy, 1903 and Farlowella amazonum (Günther, 1864) belonging to Hypostominae and Loricariinae subfamilies respectively) from Iguatemi River. Our study provide the first description regarding C-band and fluorochromic analysis in Farlowella amazonum. In Farlowella amazonum, diploid number was 58 chromosomes, with single Ag-NOR and heterochromatic blocks in centromeric regions of some chromosomes and large subtelomeric blocks were evidenced on the long arm of the pair 27, being this region CMA3+/DAPI-. The Pterygoplichthys anisitsi showed diploid number equal 52 chromosomes, with single Ag-NOR and heterochromatic blocks in centromeric and telomeric regions of some chromosomes and conspicuous large telomeric blocks on the long arm of the pair 10, being this region CMA3+/DAPI-. The results show that karyotype formula is nonconservative in Pterygoplichthys anisitsi and Farlowella amazonum.

The genus Astyanax is relatively common and encompasses various similar taxa forming a highly complex group that is difficult to precisely delimit. The present study aims to analyze cytogenetically and morphologically specimens of A. altiparanae belonging to distinct populations of the Iguatemi River Basin, Mato Grosso do Sul State, Brazil, for a better understanding of the evolutionary processes in this fish group. This study analysed 32 specimens of Astyanax altiparanae from Iguatemi River basin, MS, Brazil: 24 from the Água Boa stream and 8 from the Santa Maria stream. All specimens showed a diploid number equal to 50 chromosomes with differences in the karyotypic formula and types of chromosomes bearing the NOR between the two localities. The constitutive heterochromatin showed interstitial markings evident in the region of some chromosomes in both populations. In the morphometric analysis, the first three axes were retained for interpretation which together explained 81% of variance, showing morphometric distinction between populations. Chromosomal and morphometric data obtained may be useful for taxonomic and phylogenetic studies in this group of fish.

Moenkhausia sanctaefilomenae is a small freshwater characid fish that shows a conserved karyotype with respect to the standard genome, but also carries B microchromosomes. In the present study, one population of M. sanctaefilomenae from the Upper Paraná River basin was cytogenetically characterized, with emphasis on the analysis of B chromosomes. The M. sanctaefilomenae individuals showed a karyotype consisting of 2n=50 chromosomes with eight metacentrics, 36 submetacentrics, and six subtelocentrics, and a FN value of 100 in both sexes. In addition to the basic karyotype, all male and female individuals presented a variation from zero to eight B microchromosomes in mitotic metaphases. A secondary constriction was evident in the terminal region of the short arm of the subtelocentric pair 24, which corresponds to the Ag-NORs location. Analysis of the constitutive heterochromatin patterns by C-banding showed heterochromatic blocks in the centromeric and pericentromeric regions in most of the chromosomes. However, the B chromosomes were faintly stained with C-banding, similar to euchromatin in the A chromosomes. Aspects regarding the differences in the number and C-banding pattern of B chromosomes are discussed.

Hypoptopomatinae is a monophyletic subfamily that includes 147 species, distributed in 20 genera. Otothyropsis is a genus of Hypoptopomatinae, recently described. Here, we provided the first cytogenetic information of Otothyropsis. The specimens were collected from córrego Dourado, a small tributary of rio Iguatemi, which flows into rio Paraná. The specimens of Otothyropsis cf. polyodon were analyzed with respect to diploid number, C-Band and Ag-NOR patterns. The diploid number was 54 chromosomes, distributed in 18 metacentric, 28 submetacentric, and 8 subtelocentric chromosomes, with single Ag-NOR and conspicuous heterochromatic blocks on the short and long arms of the 24 th pair of chromosomes. Our study highlights the conservation trend of the diploid number (2n=54) and fundamental number (FN = 108) among the species of Hypoptopomatinae. However, the karyotype formula (18m+28sm+8st) seems to be specific to O. cf. polyodon, considering the other Hypoptopomatinae species already analyzed.Hypoptopomatinae é uma subfamília monofilética que inclui 147 espécies distribuídas em 20 gêneros, sendo Otothyropsis um gênero recentemente descrito. Aqui, fornecemos a primeira informação citogenética do gênero Otothyropsis. Espécimes foram coletados no córrego Dourado, um pequeno tributário do rio Iguatemi, o qual deságua no rio Paraná. Espécimes de Otothyropsis cf. polyodon foram analisados em relação ao número diploide e padrões de Banda-C e Ag-NOR. O número diploide foi de 54 cromossomos, distribuídos em 18 metacêntricos, 28 submetacêntricos e 8 subtelocêntricos, com Ag-NOR simples e blocos heterocromáticos evidentes no braços curto e longo do par de cromossomos 24. Nosso estudo destaca a tendência de conservação do número diploide (2n=54) e número fundamental (NF=108) entre as espécies de Hypoptopomatinae. Entretanto, a fórmula cariotípica (18m+28sm+8st) parece ser específica para O. cf. polyodon, considerando as outras espécies de Hypoptopomatinae já analisadas.