Population genetic structure revealed by a school of the freshwatermigratory fish, Brycon hilarii

It is believed that different genetic populations of migratory fishes can co-exist in a single hydrographic system. Although different populations may occupy and explore the river together, they segregate during the spawning season and consequently the population genetic structuring is maintained. Genetic variation of a Brycon hilarii spawning school and samples from different collection sites in the Miranda River basin were surveyed using seven microsatellites. Population structuring was revealed by a significant differentiation of the spawning school related to the supposed local populations. The genetic differentiation detected may be supported by behavior during the reproductive season that promotes the maintenance of the genetic integrity of different populations. These data may contribute toward the understanding of the behavior and biology of these fish as well as fishery management and species conservation programs

Karyotype similarity between two sympatric Schizodon fish species (Anostomidae, Characiformes) from the Paraguay River basin

Fish of the neotropical family Anostomidae generally show low karyotype variability. Nevertheless, karyotype variants have been identified within some genera, providing information about their evolutionary history. Species of the genus Schizodon show a high degree of morphological and ecological similarity compared to other anostomids. In the present study, karyotype characteristics of Schizodon borelli (40 individuals) and S. isognathum (one individual), two sympatric species found in the Paraguay River basin, were studied. C-banding, GC-specific fluorochrome Mitramycin (MM) and Ag staining as well as in situ hybridization (FISH) with rDNA probes were used. The karyotypes of these species were found to be very similar. Only two NORs were detected in a common chromosome pair of both species under Ag, MM and FISH treatments. Similar heterochromatin distribution patterns were also observed. A parallelism between the small karyotype variation and low morphological and ecological divergence observed for this genus is discussed. Their karyotype homogeneity might be related to populational features or, alternatively, might indicate that the maintenance of a symmetric and conserved karyotype structure represents optimal genomic organization among these fish

Population genetic structure revealed by a school of the freshwatermigratory fish, Brycon hilarii Estructura genética poblacional revelada por un cardumen del pez migratorio de agua dulce, Brycon hilarii

It is believed that different genetic populations of migratory fishes can co-exist in a single hydrographic system. Although different populations may occupy and explore the river together, they segregate during the spawning season and consequently the population genetic structuring is maintained. Genetic variation of a Brycon hilarii spawning school and samples from different collection sites in the Miranda River basin were surveyed using seven microsatellites. Population structuring was revealed by a significant differentiation of the spawning school related to the supposed local populations. The genetic differentiation detected may be supported by behavior during the reproductive season that promotes the maintenance of the genetic integrity of different populations. These data may contribute toward the understanding of the behavior and biology of these fish as well as fishery management and species conservation programs.<br>Se ha documentado que diferentes poblaciones genéticas de peces migratorios pueden coexistir en un único sistema hidrográfico. Diferentes poblaciones pueden ocupar y explorar el río juntas, pero se segregan durante la temporada de desove y consecuentemente la estructuración genética poblacional se mantiene. La diversidad genética de un cardumen reproductivo de Brycon hilarii y muestras de diferentes sitios en la cuenca del Río Miranda fueron analizadas mediante siete microsatélites. La estructura poblacional fue revelada por una diferenciación genética significativa del cardumen reproductivo con las muestras de las poblaciones locales. La diferenciación genética detectada puede ser resultado de un probable comportamiento durante la temporada reproductiva, que promueve el mantenimiento de la integridad genética de las diferentes poblaciones. Estos datos pueden contribuir a la comprensión del comportamiento y biología de estos peces, así como amparar programas de gestión de la pesca y conservación de las especies

RAPD markers indicate the occurrence of structured populations in a migratory freshwater fish species

Many factors have contributed to the destruction of fish habitats. Hydroelectric dams, water pollution and other environmental changes have resulted in the eradication of natural stocks. The aim of this study was to detect the genetic variation in Prochilodus marggravii from three collection sites in the area of influence of the Três Marias dam (MG) on the São Francisco river (Brazil), using the RAPD technique. The results obtained revealed that the fish in the downstream region nearest the dam have a higher similarity coefficient than those from the other sampling sites that may be related to differences in environmental characteristics in these regions. Additionaly, significant differences in the band frequencies were observed from one collection site to another. These both findings suggest the occurrence of a structured population and have important implications for the conservation of the genetic variability of distinct natural P. marggravii stocks

Karyotype similarity between two sympatric Schizodon fish species (Anostomidae, Characiformes) from the Paraguay River basin

Fish of the neotropical family Anostomidae generally show low karyotype variability. Nevertheless, karyotype variants have been identified within some genera, providing information about their evolutionary history. Species of the genus Schizodon show a high degree of morphological and ecological similarity compared to other anostomids. In the present study, karyotype characteristics of Schizodon borelli (40 individuals) and S. isognathum (one individual), two sympatric species found in the Paraguay River basin, were studied. C-banding, GC-specific fluorochrome Mitramycin (MM) and Ag staining as well as in situ hybridization (FISH) with rDNA probes were used. The karyotypes of these species were found to be very similar. Only two NORs were detected in a common chromosome pair of both species under Ag, MM and FISH treatments. Similar heterochromatin distribution patterns were also observed. A parallelism between the small karyotype variation and low morphological and ecological divergence observed for this genus is discussed. Their karyotype homogeneity might be related to populational features or, alternatively, might indicate that the maintenance of a symmetric and conserved karyotype structure represents optimal genomic organization among these fish