No abstract

Aim Sea‐level changes and coastal geomorphology (extension of continental shelves) have affected the pattern of diversification of brackish/freshwater fish populations due to the confluence of basins/estuaries during low sea‐level periods (opportunity) and isolation during high sea‐level periods. It is hypothesized that populations from estuaries in extensive continental shelves, which have greater potential for confluence, should have more opportunities for gene exchange than those in narrow continental shelves. To test this, we assessed the distribution of the genetic diversity and the patterns of diversification of the estuarine silverside, Atherinella brasiliensis, from the Brazilian coast. Location Eight estuaries along the southern and north‐eastern portions of the Brazilian coast. Materials and methods Sequences of the mitochondrial control region (D‐loop) and the cytochrome B were used to assess the distribution of genetic diversity, and these mitochondrial fragments and two nuclear introns were used to assess the patterns of diversification of A. brasiliensis. The palaeochannels that were exposed along the Brazilian coast during the Last Glacial Maximum were reconstructed using bathymetry data and the GIS method. Results The populations of A. brasiliensis from the estuaries of the north‐eastern Brazilian coast (narrower and shallower continental shelf) showed higher levels of genetic differentiation and larger (more haplotypes) endemic lineages than the populations in the southern coast (broader and deeper continental shelf). Furthermore, south coast lineages showed more evidence of genetic exchange among populations, which have resulted in a reticulated relationship between lineages and estuaries. The reconstruction of palaeochannels revealed more connections among southern than north‐eastern basins. Main conclusions Our results support the hypothesis that continental shelf extension and sea‐level changes have influenced the diversification of A. brasiliensis. By extension, they also support the hypothesis of diversification by taxon pulse, which makes predictions based on the opportunities for expansion during periods of low sea level and the width of the continental shelf. We suggest this as a model for the genetic diversification and distribution of estuarine species along the Brazilian coast and other regions of the world.

Among oysters, species of Crassostrea (Sacco, 1897) are the most attractive to aquaculture. In Brazil, the genus is represented by C. rhizophorae (Guilding, 1828) and C. brasiliana (Lamarck, 1819). Because the maturation and breeding technology is not well developed for these species, aquaculturists need a reliable method to decide the correct time to place spat collectors in the field, and to identify both species, which are morphologically similar. In this study a specific Multiplex PCR protocol was developed, using one pair of universal primers from 18S rDNA as a positive control and a pair of specific primers for each target species. The sensitivity and specificity of the protocol was evaluated. It detected C. rhizophorae DNA in low concentrations, and C. brasiliana DNA in even lower concentrations. Further, the Multiplex PCR proved efficient in detecting DNA in concentrations equivalent to that of a single larva of each species, either separated or combined, when mixed with total DNA extract of a plankton sample representing 1000 L of filtered water. Field tests confirmed the applicability of the protocol, which holds the promise to become an important tool for aquaculture or conservation programs, allowing for the continuous monitoring of the life cycle of C. brasiliana and C. rhizophorae, by detecting the right periods of larval release and settlement

Neste trabalho o objetivo foi determinar o tamanho médio ótimo da malha a ser usada no dimensionamento de redes-de-emalhar mais seletivas para captura da cavala na costa Amazônica. A seletividade da pescaria é definida como a probabilidade relativa de se capturar peixes com uma determinada amplitude de comprimento por uma arte de pesca em particular, em uma situação na qual todos os peixes têm a mesma chance de irem de encontro à rede e serem capturados. Para a realização deste trabalho, foi calculado o perímetro máximo, correspondente ao comprimento zoológico da primeira maturação sexual e foi obtido o comprimento médio da malha estirada. Para o cálculo do comprimento médio ótimo da malha, foi considerada a relação entre a compressibilidade do corpo do animal, ao tentar passar pela malha, e a elasticidade do fio da panagem, mediante a ação da força de natação com que o peixe entra na malha. Essa relação foi calculada usando-se o modelo linear através do método dos mínimos quadrados, com as variáveis obtidas medindo-se o perímetro máximo dos espécimes e o perímetro das malhas onde foram, respectivamente, capturados. Foi usada uma rede-de-emalhar confeccionada artesanalmente com fios de poliamida monofilamento. O valor obtido para o perímetro máximo, correspondente ao comprimento zoológico da primeira maturação sexual, foi de 303,5 mm, o comprimento médio da malha que foi de 151,8 mm. O valor obtido para o comprimento médio ótimo do lado da malha para captura da cavala com redes-de-emalhar foi de 124 mm.