Field‐Deployable FTA Card for Sampling, Storage and Detection of <i>Aeromonas</i> spp. in Rainbow Trout: Four‐Year Ambient DNA Stability Validated

ABSTRACT Bacterial pathogen detection in rainbow trout ( Oncorhynchus mykiss , Walbaum 1792) aquaculture typically involves multi‐step procedures, including sample transport, bacterial isolation, culture and subsequent molecular analysis. Aeromonas salmonicida and Aeromonas hydrophila are major pathogens causing significant losses; however, conventional diagnostic workflows are time‐consuming and require cold‐chain logistics and contamination‐prone handling steps. This study evaluated FTA cards for direct pathogen detection from infected trout tissues without culture, integrating sampling, DNA preservation and PCR‐based analysis into a single workflow, targeting two virulence ( aerA , hlyA ), two housekeeping ( gyrB , rpoD ) and one antibiotic resistance ( sul2 ) genes. The performance of the FTA‐based approach was compared with a standard commercial DNA extraction kit (QIAamp) using tissue samples from 62 rainbow trout collected from commercial farms in Türkiye ( n = 200 FTA card samples). PCR amplification from FTA cards was successful for all five target genes in 100% of tested samples, yielding amplicons of equivalent sizes and band intensities to those obtained from kit‐extracted DNA. DNA extraction from FTA cards was completed in less than 1 h, with an estimated per‐sample cost of approximately $1–$2. All five target genes were also successfully amplified from a subset of 50 cards stored at ambient temperature for 4 years (50/50 cards; 100% amplification success). The simplified workflow allows on‐site sampling by farm personnel and shipping at ambient temperature, reducing logistical challenges associated with sample transport and storage. These findings indicate that FTA cards provide a practical and reliable alternative for transport, storage and preservation of Aeromonas spp., particularly for field‐based applications where rapid processing and simplified sample handling are required.