Genetic Diversity of Cultured Rainbow Trout (Oncorhynchus mykiss) Populations in Türkiye Based on Mitochondrial DNA Cytochrome b (cyt-b) Sequence Analysis

This study aimed to investigate the genetic diversity and structure of rainbow trout (Oncorhynchus mykiss) cultured populations in different provinces of Türkiye, based on the cytochrome b (cyt-b) gene region of mitochondrial DNA (mtDNA). Tissue samples were collected from a total of 98 fish (seven fish per province) across 14 provinces, followed by DNA isolation. The mtDNA cyt-b gene region (754 bp) was amplified using PCR. Genetic diversity indices, genetic structure, and phylogenetic analyses were calculated from the cyt-b gene sequence data. The average nucleotide frequencies of the four nucleotides cytosine (C), thymine (T), adenine (A), and guanine (G) were found to be 26.2%, 24.9%, 26.2%, and 22.8%, respectively, with a higher A + T content (51%) compared to G + C content (49%). A total of 645 polymorphic nucleotides were identified across the 14 populations, and 50 distinct haplotypes were defined. Haplotypic diversity ranged from 0.91 to 0.48, while nucleotide diversity (π) varied between 0.26 and 0.00. The highest genetic diversity was observed in the Tokat and Van populations, whereas the lowest was recorded in the Elazığ and Kahramanmaraş populations. AMOVA analyses revealed that 71.1% of the genetic diversity was found between populations, while 28.9% was found within populations. Pairwise FST values ranged from 0.38 to 0.99, with an average FST of 0.71. Phylogenetic analyses indicated that the populations clustered into two main groups, with further sub-groupings within these clusters. Notably, the Kahramanmaraş and Elazığ populations were found to be significantly differentiated from other populations. In conclusion, despite rainbow trout not being a native species in Türkiye, the findings of this study indicate that the genetic diversity of the populations is at a good level. However, in order to preserve the genetic diversity of cultured rainbow trout populations and to increase effective population size, it is recommended that breeders engage in fry exchanges and import new rainbow trout specimens to enhance genetic diversity.