Distribuição da variabilidade genética da pescada, plagioscion squamosissimus (heckel, 1840) na calha do Rio Amazonas

Abstract

The South American silver croaker Plagioscion squamosissimus, is a sciaenid restricted to freshwaters of South America. It has a wide distribution within the Brazilian territory, originally found in the Amazonian basin and introduced in northeast and southeast of Brazil. This species is important for the fishing economy of the Amazonian area, being considered a noble fish species and being of great commercial value. However, there is still no fisheries management project that would allow its conservation. Applied genetic-population studies to species of fish of commercial importance have been generating data of extreme importance for a more appropriate delimitation of fishery stocks. Knowing the distribution of genetic diversity of populations of South American silver croaker in the main channel of the river Amazon, one can obtain data that contribute to the appropriate management of this species in this area, and, consequently, its conservation. Five localities of the Amazon River were sampled, with a total of 81 individuals collected. The genomic DNA was extracted from fins using 2% CTAB, and the control region of the mitochondrial DNA was amplified and sequenced on the ABI 3130 XL automatic sequencer. A total of 727 base pairs (bp) were aligned and edited in the program BioEdit v. 5.0.6. resulting in 54 haplotypes. Results generated in the program Arlequin v. 3.1 also showed the existence high levels of genetic diversity for this specie as seen in elevated value of average genic diversity (Ĥ=0.9778), and in the high values of the average nucleotide diversity (π=0.016300). These results suggest absence of overexploitation of the South American silver croaker populations, specially at the mitochondrial DNA control region. The results of AMOVA indicate that 93,68% of the total genetic variance was observed within sampling localities, and only 6,32% explains between-locality variance. The ΦST value of 0,06319 indicates low but significant (P=0,00673) differentiation among localities. The absence of differentiation between localities was inferred based on the lack of significant pair-wise ΦST values after Bonferroni correction. These results showed that the only significant comparison was between Tabatinga Soure which are the two extreme-most localities in our analysis. These results imply that P. squamosissimus most likely forms a single population in the main channel of the Amazon River along a distance of at least 2300 km. Genetic differentiation of the two extreme localities may be the result of isolation-by-distance, however, we did not observe significant correlation between genetic and geographic distances. Population expansion was observed among the most distant points of the sample distribution.