ABSTRACT This study aimed to impute the genetic makeup of individual fishes of Serrasalmidae family on the basis of body weight and morphometric measurements. Eighty-three juveniles, belonging to the genetic groups Pacu, Pirapitinga, Tambaqui, Tambacu, Tambatinga, Patinga, Paqui and Piraqui, were separated into 16 water tanks in a recirculation system, with two tanks per genetic group, where they remained until they reached 495 days of age. They were then weighed and analyzed according to the following morphometric parameters: Standard Length (SL), Head Length (HL), Body Height (BH), and Body Width (BW). The identity of each fish was confirmed with two SNPs and two mitochondrial markers. Two analyses were performed: one for the validating the imputation and another for imputing a genetic composition of animals considered to be advanced hybrids (post F1). In both analyses, we used linear mixed models with a mixture of normal distributions to impute the genetic makeup of the fish based on phenotype. We applied the mixed models method, whereby the environmental effects were estimated by the Empirical Best Linear Unbiased Estimator (EBLUE) and genetic effects are considered random, obtaining the Empirical Best Linear Unbiased Predictor (EBLUP) from the general (GCA) and the specific (SCA) combining ability effects. The results showed that validation of the genetic makeup imputation based on body weight can be used because of the strong correlation between the observed and imputed genotype. The fish classified as advanced hybrids had a genetic composition with a high probability of belonging to known genotypes and there was consistency in genotype imputation according to the different characteristics used.

Cariótipo e outros marcadores cromossômicos revelados pelo bandamento C e impregnação da prata (Ag) em duas populações de Astyanax bockmanni (córrego Barra Seca e rio Campo Novo) foram examinados. O número cromossômico diploide 2n = 50 e cariótipo quase idênticos são documentados. Bandamento C revelou blocos heterocromáticos na região terminal de alguns cromossomos, com um elevado nível de polimorfismos. A impregnação da prata mostrou variabilidade do número, posição e organização para as regiões organizadoras de nucléolo (RONs). Astyanax bockmanni revelou características cromossômicas similares ao complexo "A. scabripinnis" e os mecanismos responsáveis pelo alto nível do polimorfismo foram discutidos.

Karyotype and other chromosomal markers as revealed by C-banding and silver (Ag) impregnation in two Astyanax bockmanni populations (Barra Seca Stream and Campo Novo River) were examined. The diploid chromosome number 2n = 50 and nearly identical karyotypes were documented. C-banding revealed heterochromatic blocks on the terminal regions of some chromosomes, with high frequencies of polymorphisms. The Ag-impregnation showed that the nucleolus organizer regions (NORs) varied in number, location and organization. Astyanax bockmanni revealed chromosome characteristics similar those of the species complex "A. scabripinnis". Mechanisms that may be responsible for the high degree of polymorphism are discussed.

The genetic monitoring of interspecific hybrids involves the application of methodologies able to provide an easy and indubitable genetic characterization of both parental and hybrid individuals. In the present work, cytogenetic techniques were used to identify a hybrid lineage of "Piaupara" in order to caracterize them in relation to the parental species, Leporinus macrocephalus (piauçu) and L. elongatus (piapara). The cytogenetic analysis revealed that L. macrocephalus presented 2n = 54 chromosomes and a nucleolar organizer regions (NOR) at the telomere of the long arm of the submetacentric chromosome pair 2. Analysis of constitutive heterochromatin (C-banding) revealed a conspicuous block at the pericentromeric region on the long arm of a submetacentric chromosome pair. L. elongatus presented the same diploid number, 2n = 54, and a karyotypic formula similar to that of L. macrocephalus. The NORs were also at the telomere of the long arm of the submetacentric pair 2, which was morphologically different from that of L. macrocephalus. Heterochromatic blocks were observed at both telomeres of a submetacentric chromosome pair. The hybrid "Piaupara" presented the same diploid number (2n = 54) and karyotypic formula as the parental species and there were no visible differences between parental and hybrid individuals. Differently from the Giemsa staining, NOR- and C-banding analysis showed marked differences which allowed the identification of the hybrids by the different morphology and/or size of the chromosomes carrying the NORs and patterns of heterochromatin distribution in their chromosomes. Such genetic studies are important for fish culture since they can provide tools for monitoring natural and artificial hybridization. They are also useful in biological conservation programmes and in the proper management of natural and reared fish stocks.

Several species of the genus Astyanax have already been genetically studied, and B-chromosomes have been considered to be an interesting feature in some species of this group. In the present paper we report, for the first time, the occurrence of a B microchromosome in a natural population of A. altiparanae. This additional genomic element was identified as an acrocentric chromosome, similar in size to the smallest chromosomal pairs of the standard karyotype. Analysis of the constitutive heterochromatin pattern by C-banding evidenced heterochromatic blocks located on centromeric, pericentromeric, and interstitial regions of some chromosomes, and also positive marks in a subtelocentric chromosomal pair that presented the short arms entirely heterochromatic. The application of this methodology also revealed a heterochromatic pattern in the extra chromosome, a typical feature of supernumerary chromosomes.