Ancistrus Kner, 1854 is a diverse catfish genus, currently comprising 66 valid species, but karyotype data were recorded for 33 species, although only ten have their taxonomic status defined. Considerable karyotype diversity has been found within this genus, with 2n varying from 34 to 54 and structural variability including heteromorphic sex chromosomes. In many cases, uncertainty on the taxonomic status of the study populations hampers reliable interpretation of the complex chromosomal evolutionary history of the group. This study aims to present the first karyotype data for a population of the Ancistrus sp. collected in Criminoso stream (tributary of the Paraguay River Basin, Mato Grosso do Sul, Brazil) in which a combination of different chromosomal markers was used and results integrated in broad discussion on karyotype evolution in the genus. The specimens presented 2n=42 with 18m+16sm+8st and a single NOR revealed by silver nitrate and fluorescence in situ hybridization (FISH) with 18S rDNA probe, located in pair No. 10. Clusters of 5S rDNA were located in the pericentromeric region of three chromosomes: pair No. 1 (metacentric) and one of the homologues of the nucleolar pair No. 10. Heterogeneity in the molecular composition of the heterochromatin was confirmed by the association of C-banding and fluorochrome CMA3/DAPI-staining. Exploring the differential composition of constitutive heterochromatin in Ancistrus may provide an important perspective to understand genome organization and evolution within this group. Our data reinforce the chromosomal diversity present in Ancistrus genus and we discuss the potential sources these variation. The karyotype structure of Ancistrus sp. “Criminoso stream” appears to be consistent with the existence of a new candidate species.

ABSTRACT.Hypostomus is a group of fish with numerical and structural karyotypic variability. Among them, only six species, three of which belong to the Amazon basin, show a sex chromosome. In this study, we present the karyotype structure of Hypostomus cf. plecostomus from the Teles Pires river basin in the municipality of Alta Floresta, MT. The species has 2n = 68 and the karyotype formula 14m+ 24sm+ 14st+ 16a [fundamental number (FN) = 120] in males and 15m+ L.C. Oliveira et al. 6626©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 14 (2): 6625-6634 (2015) 24sm+14st+15a (FN = 121) in females and sex chromosomes ZZ/ZW. Argyrophilic nucleolar organizer regions (AgNORs) were identified in two pairs of chromosomes at different positions: short arm of the pair 21and long arm of the pair 27, matching the signals displayed by 18S FISH and indicating multiple NORs. Analysis of band C detected few blocks of constitutive heterochromatin in the pericentromeric regions of most chromosomes and the telomeric regions of some pairs, including the nucleolar pair 21. However, large blocks on the long arm of the nucleolar pair 27 still stood out. GC-rich heterochromatin (CMA 3 ) was visualized only coincidently with nucleolar sites. Mapping of 5S rDNA sites with FISH revealed markings in eight chromosomes, demonstrating synteny between the 18S and 5S sites. The data obtained for H. cf. plecostomus are important for taxonomic studies of this Amazon complex "H. plecostomus group". The occurrence of sex chromosomes in Amazon species of Hypostomus suggests an evolutionary event that is independent of other species in the group.

RESUMO:Ctenopharyngodon idella, popularmente conhecida como carpa capim, é uma espécie exótica que vem sendo bastante apreciada devido ao seu desempenho na piscicultura. O presente estudo foi conduzido na estação de piscicultura da Universidade Estadual do Paraná, campus de União da Vitória, com o objetivo de avaliar o efeito de três diferentes tipos de alimentação no desenvolvimento de alevinos da carpa capim. Foi utilizado um lote inicial padrão de peso médio 13,0 ± 0,58 g e comprimento total 10,0 ± 0,10 cm distribuídos em três unidades experimentais de 10 m 3 cada: (1) alevinos alimentados com forragens (milheto no período verão-primavera e azevém no outono-inverno); (2) alevinos alimentados com forragem associada com ração comercial 42% de proteína bruta; e (3) alimentados exclusivamente com ração comercial. Os resultados obtidos demonstraram diferenças significativas entre os tratamentos (p < 0,05), apesar dos tratamentos apenas com forragem e forragem consorciada com ração não diferirem estatisticamente. A relação pesocomprimento dos respectivos tratamentos foi descrito pelas seguintes equações: y = 0,013x 2,990 ; y = 0,012x 3,002 ; y = 0,018x 2,882 , e assim somente para o tratamento exclusivo com ração o crescimento foi alométrico (b < 3,0). Não houve diferença significativa no fator de condição relativo entre os tratamentos (p > 0,05). Embora para C. idella o crescimento seja melhor com dietas suplementadas com ração, no presente estudo o tratamento exclusivo com milheto ou azevém mostrou taxas de crescimento entre as superiores.

ABSTRACT. The Iguaçu River basin is a tributary to the upper Paraná River in southern Brazil, and is considered an important aquatic ecoregion that, although having few species of fish, 51-71% of these are apparently endemic. Ancistrus abilhoai is one of three recently described species for this basin and is currently considered endemic to the basin. In this study, we present the chromosomal structure of two populations of Ancistrus abilhoai one collected in the Iguaçu River, in Paraná State, and another collected in the Timbó River, a tributary of the Iguaçu River, in the State of Santa Catarina. Karyotype analyzes were performed in 11 specimens from the Iguaçu River (four females and seven males) and 12 specimens (all males) from Timbó River, revealing 2n = 48 chromosomes with a karyotype formula of 22m + 14sm + 6st + 6a in both populations. Analysis of active nucleolar organizer regions (Ag-NORs) and fluorescent in situ hybridization (FISH) with 18S rDNA probes revealed the submetacentric pair 13 bearing marks at terminal positions on the short arms. Considered as plesiomorphic chromosomal markers in Loricariidae, asynteny 18S and 5S rDNA, and small amounts of heterochromatin were observed. In this study, the first chromosomal data of A. abilhoai are presented with comments on karyotypic characteristics of the genus.

In the present study, we analyzed individuals of Hypostomus soniae (Loricariidae) collected from the Teles Pires River, southern Amazon basin, Brazil. Hypostomus soniae has a diploid chromosome number of 2n = 64 and a karyotype composed of 12 metacentric (m), 22 submetacentric (sm), 14 subtelocentric (st), and 16 acrocentric (a) chromosomes, with a structural difference between the chromosomes of the two sexes: the presence of a block of heterochromatin in sm pair No. 26, which appears to represent a putative initial stage of the differentiation of an XX/XY sex chromosome system. This chromosome, which had a heterochromatin block, and was designated proto-Y (pY), varied in the length of the long arm (q) in comparison with its homolog, resulting from the addition of constitutive heterochromatin. It is further distinguished by the presence of major ribosomal cistrons in a subterminal position of the long arm (q). The Nucleolus Organizer Region (NOR) had different phenotypes among the H. soniae individuals in terms of the number of Ag-NORs and 18S rDNA sites. The origin, distribution and maintenance of the chromosomal polymorphism found in H. soniae reinforced the hypothesis of the existence of a proto-Y chromosome, demonstrating the rise of an XX/XY sex chromosome system.