Molecular Screening for Tetracapsuloides bryosalmonae (Malacosporea) in Farmed Rainbow Trout (Oncorhynchus mykiss) from Samsun, Türkiye

Myxozoans represent an important group of metazoan endoparasites. Tetracapsuloides bryosalmonae is a myxozoan parasite belonging to the class Malacosporea and is the causative agent of proliferative kidney disease in salmonid fish. This parasite poses a serious threat to both farmed and wild salmonid populations in Europe and North America. In Türkiye, there has been no report on the presence of T. bryosalmonae in salmonid fish to date. This study aimed to investigate, for the first time, the presence of T. bryosalmonae in farmed rainbow trout (Oncorhynchus mykiss) reared in floating net cages in Derbent Dam Lake, Samsun, Türkiye using molecular methods. Between July 2024 and February 2025, necropsies were performed on a total of 150 rainbow trout weighing 150–250 g. Tissue samples were collected from the anterior and posterior kidneys of each fish, and DNA isolation was performed from these tissues. The presence of T. bryosalmonae DNA in kidney-derived DNA samples was screened using multiplex PCR. Tetracapsuloides bryosalmonae DNA was not detected in any of the 150 rainbow trout samples examined by molecular screening. This study provides the first epidemiological data indicating that T. bryosalmonae was not detected in rainbow trout farmed in Derbent Dam Lake, Samsun. However, more comprehensive molecular screening studies are needed to determine the presence of T. bryosalmonae in both farmed salmonid species and wild salmonid populations inhabiting natural environments across different geographical regions of Türkiye.