The genetic difference between the two sides of the basin may be due to two reasons: natural capture and long-distance diffusion between the two basins are accompanied by fish migration between the basins. The founder effect caused by artificial transfer of a small amount of trout to the fish-free habitat in Grand, casas, may limit the diversity of effective alleles, resulting in the diffusion pattern of trout between the two basins. Microsatellite FSAT pairing analysis supported the genetic association among trout populations in the basin (P = 0.1166; The initial value of α = 0.00064 1) was adjusted, but there was a significant difference between casas Grand Trout and the artificial breeding population in the western Period Valley of Babis. In 1996, there are significant genetic frequency differences among trout collected by La Escalariado, Rio Gavilan Las Guacamayes and Segundo de Mayo (p=0.0005 in both cases). In the comparison of FSTAT matched pairs, there was no significant difference between the allele frequencies of Rio Cumbres Las Palmas trout in the east of the basin and those of Rio Gavilan trout (P = 0.1Kloc-0/55) or Segundo de Mayo trout (p = 0.002), which indicated that the fish population had recently migrated to the basin. However, it is not excluded that natural and human factors play a role in the construction of trout population in the Grand Basin of casas. The large number of trout samples found at other sampling points and on both sides of the watershed helps to explain this contradiction. The second important discovery of this study is the relationship between the southern irrigation area of Rio Yaqui and the trout population of Rio Mayo (Rio Tutuca and Rio Chico). Although the topography of a deeply fractured canyon conceals the evidence of any major river basin connection, in the distant past, it was very possible to complete the inter-basin transfer by connecting the fault trough between rios Yaqui and Mayo (King,1939; Hendrickson, 1980). Our microsatellite data support this inference, indicating that the genetic relationship between rios Tutuca, Chico and Mayo trout is closer than that between Rio de Bavispe trout and other trout populations. Ssa 14 loci were not amplified in these three loci, suggesting that this population needs further research including sequence analysis.