Abstract
Background:
Pseudomonas aeruginosa is an opportunistic pathogen in aquaculture, capable of causing significant infections and spreading through genetically diverse strains.

Aim:
This study investigated the clonal relatedness and genotyping analysis of Pseudomonas aeruginosa isolates from infected salmon trout in various trout farms using Random Amplified Polymorphic DNA (RAPD) PCR fingerprinting.

Methods:
A total of 35 isolates were collected from lesions in different organs of trout from seven farms across Sheladize and Amedi districts in Duhok province, Iraq. RAPD-PCR was performed using specific primers, and amplified DNA fragments were analyzed via GelJ software to generate a dendrogram based on UPGMA clustering.

Results:
The results showed a genetic similarity range of 50.00% to 100.00%, identifying 33 unique genotypes. Notably, two isolates from different farms and geographic locations shared the same genotype, indicating potential bacterial transmission. However, the rest of the strains were grouped into a single genotype due to significant genetic diversity seen among their DNA.

Conclusion:
The findings emphasize the role of bacterial clonal differentiation in the spread of P. aeruginosa infections in fish farms, driven by multiple transmission sources. This genetic variation highlights the need for enhanced biosecurity measures to mitigate the spread of P. aeruginosa in aquaculture settings.

Key words: Pseudomonas aeruginosa, Salmon trout, RAPD-PCR, Genetic diversity