Abstract
The arapaima, Arapaima gigas, is a fish whose populations are threatened by both overfishing and the ongoing destruction of its natural habitats. In the Amazon basin, varying levels of population structure have been found in A. gigas, although no data are available on the genetic diversity or structure of the populations found in the Araguaia-Tocantins basin, which has a topographic profile, hydrological regime, and history of fishing quite distinct from those of the Amazon. In this context, microsatellite markers were used to assess the genetic diversity and connectivity of five wild A. gigas populations in the Araguaia-Tocantins basin. The results of the analysis indicated low levels of genetic diversity in comparison with other A. gigas populations, studied in the Amazon basin. The AMOVA revealed that the Arapaima populations of the Araguaia-Tocantins basin are structured significantly. No correlation was found between pairwise FST values and the geographical distance among populations. The low level of genetic variability and the evidence of restricted gene flow may both be accounted for by overfishing, as well as the other human impacts that these populations have been exposed to over the years. The genetic fragility of these populations demands attention, given that future environmental changes (natural or otherwise) may further reduce these indices and eventually endanger these populations. The results of this study emphasize the need to take the genetic differences among the study populations into account when planning management measures and conservation strategies for the arapaima stocks of the Araguaia-Tocantins basin.
Highlights
Worldwide, the populations of many fish species are declining rapidly (Allan et al, 2005), with the communities occupying lakes, rivers and floodplains being the most affected (Abell et al, 2008)
This study is the first to use microsatellite markers to examine the genetic diversity of the arapaima populations of the AraguaiaTocantins basin
The arapaima populations that inhabit the study region are affected by natural processes, in particular the hydrological regime, that are quite distinct in comparison with the populations found in the Amazon basin, the region in which the species has been investigated in most detail (Vitorino et al, 2015)
Summary
The populations of many fish species are declining rapidly (Allan et al, 2005), with the communities occupying lakes, rivers and floodplains being the most affected (Abell et al, 2008). As the arapaima prefers the lentic environments, such as flooded forests, rivers and lakes, of the Amazon, Araguaia-Tocantins and Essequibo basins (Castello and Stewart, 2010; Castello et al, 2013), its populations become increasingly concentrated during the dry season, and the high densities of fish that accumulate during this period greatly increase their vulnerability to capture Given this vulnerability of the species to fishing and the reduction of its stocks in recent years, researchers have focused increasingly on its genetic diversity and population structure (Farias et al, 2003; Hrbek et al, 2005, 2007; Hrbek and Farias, 2008; Hamoy et al, 2008; Araripe et al, 2013; Vitorino et al, 2015), chromosomal evolution (Marques et al, 2006), and other aspects of its biology (Gomes, 2007; Castello, 2008a,b; Arantes et al, 2010; Fernandes et al, 2012; Farias et al, 2015)
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