Genetic Structure and Diversity in Wild and Cultivated Populations of the Mangrove Oyster Crassostrea gasar from Southern Brazil.

The mangrove oyster (Crassostrea gasar) is Brazil's second most cultured species and presents a high potential for aquaculture. However, artificial selection in a highly fecund species and significant variance in reproductive success can result in the loss of genetic diversity and increases the inbreeding rate, especially in cultivated populations. In this study, we investigated the genetic structure and diversity of C. gasar in wild and cultivated populations using 14 microsatellites. Spatial genetic comparisons revealed the existence of two main genetic groups of C. gasar, one comprising the population in cultivation and the other formed by wild populations along the southern and southeastern Brazilian coasts. Although no common genetic structure exists among wild populations, it is possible to observe a distribution gradient based on discriminant analysis of principal components consistent with their geographic distribution. However, it is insufficient to differentiate them genetically. Despite artificial reproduction, the genetic diversity values of the cultivated population remained relatively high and did not show a reduction. Therefore, monitoring the cultivated population and establishing reference values for genetic diversity will allow the adoption of strategies both for the viability of the cultivated population and the management of wild populations.

Genetic characterization of the Neotropical catfish Pimelodus maculatus (Pimelodidae, Siluriformes) in the Upper Uruguay River.

Freshwater fish present unique challenges when one attempts to understand the factors that determine the structure of their populations. Habitat fragmentation is a leading cause of population decline that threatens ecosystems worldwide. In this study, we investigated the conservation status of genetic variability in the Neotropical catfish (Pimelodus maculatus). Specifically, we examined the structure and genetic diversity of this species in a region of the Upper Uruguay River fragmented by natural barriers and dams. There was no genetic structure among the four sites analyzed, indicating the existence of only one population group. A combination of environmental management and genetic monitoring should be used to minimize the impact of impoundment on panmitic populations of migratory fish species.