Abstract
Freshwater amphipods of the genus Gammarus are important trophic components of aquatic ecosystems and are increasingly considered a potential bioresource for aquaculture. However, their role in the maintenance and transmission of infectious agents remains poorly understood. This study evaluated the presence of major crustacean and fish pathogens in Gammarus lacustris populations from Kazakhstan and characterized associated viral communities using metagenomic sequencing. Six pooled samples collected from freshwater ecosystems across Kazakhstan were screened using PCR and RT-PCR assays targeting World Organisation for Animal Health (WOAH)-listed pathogens, including White Spot Syndrome Virus, Taura Syndrome Virus, Infectious Myonecrosis Virus, Aphanomyces astaci, and Aphanomyces invadans. In parallel, high-throughput sequencing (Illumina NovaSeq) was performed to assess virome composition and structure. No WOAH-listed pathogens were detected, suggesting a low detectable occurrence of major notifiable agents under the conditions of the present study. Metagenomic analysis revealed a virome dominated by RNA viruses, particularly picorna-like viruses (Picornaviridae), Dicistroviridae, and Marnaviridae. Phylogenetic and genome organization analyses identified potentially novel or highly divergent viral lineages within Picornavirales. Collectively, these findings suggest a favorable epizootiological profile of G. lacustris populations while highlighting freshwater amphipods as hosts of diverse and partially uncharacterized viral communities relevant to aquatic disease surveillance and aquaculture biosecurity.