Determination of hybridization and cross-breeding status of brown trout (Salmo trutta) distributed in Turkey

Brown trout (Salmo trutta) is a widely distributed fish species belonging to the Salmonidae family. It's naturally distributed across our country. Taxonomic status of the Brown trout is controversial, yet numerous new species of Salmo trutta were discovered from different populations. In this study, the genetic diversity of Salmo trutta, sampled from 37 different populations in 12 different basins, was evaluated. In this thesis, two mtDNA gene regions (COI, cyt-b), the control region (d-loop) that regulates mtDNA replication and transcription, and the nuclear ITS region were analyzed. Additionally, 16 microsatellite loci were used to determine genetic diversity among populations. 20 haplotypes were determined in the COI gene region, 23 haplotypes in the cyt-b gene region, 93 haplotypes in the d-loop region, and 5 haplotypes in the ITS region. It was determined that the gene regions that best reflect the distinction between populations are the cyt-b gene region and d-loop regions. As a result of microsatellite data analysis, 4 of the 16 loci could not be amplified, and they were not included in the analysis. Based on the results performed with the remaining 12 loci, it was determined that there was a low level of genetic variation between populations. According to the results of the spatial variation analysis, the populations showed spatial homogeneity, and there was no significant relationship between geographical distance and genetic distance. In the parent analysis, in 25 of the 36 populations sampled from 12 basins, all parental assignments consist of individuals belonging to the same parts; in the remaining 11 populations, those that can be kept from different parts are stopped. Of the 25 populations sampled, individuals from different basins did not hybridize. In the light of the results obtained, it was determined that the genetic difference between populations with different S. trutta species was low, and species definitions based on single gene region analysis were insufficient. Sequence analysis and microsatellite analysis results indicate that the brown trout distributed in our country are populations of a single species. Therefore, defining new species solely based on morphological characteristics and a few base differences in the mitochondrial cyt-b gene region can be highly misleading.