Salmo trutta, commonly known as brown trout, is an invasive species that has established itself in various regions, including South Korea, where it poses ecological risks to native freshwater fish populations. To enable natural habitat restoration, S. trutta needs to be monitored, but traditional monitoring techniques are associated with several limitations. Therefore, in this study, we aimed to apply a sensitive and specific real-time PCR (qPCR) assay using a set of primers and a hydrolysis probe specific to the mitochondrial cytochrome b gene of S. trutta. Environmental DNA (eDNA) was extracted from river-water samples collected downstream of the Soyang Reservoir and around the Uiam Reservoir between January and March 2023. The qPCR assays successfully detected S. trutta eDNA in 11 of the 24 samples, with high concentrations found upstream and downstream of the Soyang River. Our results demonstrate the effectiveness of qPCR assay for the S. trutta detection in aquatic environments and highlight its potential for monitoring the spread of this species, especially in areas that are difficult to survey using traditional methods. This molecular approach offers a more efficient tool for S. trutta population management, mitigating its impact on native biodiversity.

Japanese eel endothelial cells-infecting virus (JEECV) and Anguillid herpesvirus 1 (AnHV) are major pathogens in farmed eels. JEECV causes eel viral endothelial cell necrosis (VECNE), while AnHV leads to symptoms such as head erythema and gill necrosis. Both viruses cause severe mortality alone or in combination, necessitating rapid and early detection of their presences. In this study, we developed a highly efficient duplex quantitative PCR method (r² = 0.999) using hydrolysis probes for the rapid and simultaneous detections of AnHV and JEECV. This new diagnostic method demonstrated a 1.7-fold higher detection rate for AnHV and a 2.5-fold higher detection rate for JEECV than conventional PCR. Quantitative analysis of water and eel tissue samples from aquaculture facilities revealed that the two viruses could be detected in water 1–3 months prior to mortality, enabling their early identification of infections through water testing alone. Notably, the method reliably detected low viral loads (< 1 copy) in both water and tissue samples, facilitating preclinical detection and proactive disease management. This approach reduces the risk of mass mortality and economic losses in eel farming. This study underscores the critical role of advanced molecular diagnostic technologies in enhancing health management in aquaculture.

Salmo trutta, commonly known as brown trout, is an invasive species that has established itself in various regions, including South Korea, where it poses ecological risks to native freshwater fish populations. The Ministry of Environment of South Korea has legally designated S. trutta as an invasive species. Thus, to enable natural habitat restoration, S. trutta needs to be monitored in South Korea. However, traditional monitoring techniques are associated with several limitations. Therefore, in this study, we aimed to apply a sensitive and specific qPCR assay using primers and a hydrolysis probe specific to the mitochondrial cytochrome b gene (mt-cyb) of S. trutta. Environmental DNA (eDNA) was extracted from river water samples collected downstream of the Soyang Reservoir and around the Uiam Reservoir between January and March 2023. The qPCR assays successfully detected S. trutta eDNA in 11 of the 24 samples, with high concentrations found upstream and downstream of the Soyang River. Our results demonstrate the effectiveness of qPCR assay for the detection of S. trutta in aquatic environments and highlight its potential for monitoring the spread of this species, especially in areas that are difficult to survey using traditional methods. This molecular approach offers a more efficient tool for S. trutta population management, mitigating its impact on native biodiversity.

Mitochondrial genomes (mitogenomes) play a key role in species identification and phylogenetic studies due to their stable gene arrangements and evolutionary insights. Dryophytes flaviventris, classified in 2020 and closely related to D. suweonensis, lacks mitochondrial DNA data for differentiation. This gap hinders accurate species identification, highlighting the need for further genomic studies. The complete mitogenome size of two D. flaviventris were 18,616–18,617 bp and those for two D. suweonensis were 18,610–18,616 bp, the mitogenomes of the two species consisting of 13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 transfer RNA (tRNA) genes, and a D-loop. Phylogenetic analysis confirmed that the mitochondrial DNA of all four individuals formed a monophyletic group, showing no genetic differentiation. As a result, the two species do not form distinct clades, and mitogenomes could not differentiate them, suggesting they are not reciprocally monophyletic. This study presents the first mitogenome data for D. flaviventris and provides valuable insights into tree frog taxonomy.

The Japanese eel endothelial cell-infecting virus (JEECV) and Anguilla herpesvirus (AnHV) are major pathogens in farmed eels. JEECV causes eel viral endothelial cell necrosis (VECNE), while AnHV leads to symptoms such as head erythema and gill necrosis, respectively. Both viruses can result in severe mortality, either independently or in combination, necessitating rapid and early detection of their presence. In this study, we developed a highly efficient duplex quantitative PCR method (R² = 0.999) using TaqMan probes for the rapid and simultaneous detection of AnHV and JEECV. This new diagnostic method demonstrated a 1.7-fold higher detection rate for AnHV and a 2.5-fold higher detection rate for JEECV than those of conventional PCR. Quantitative analysis of water and eel tissue samples from aquaculture facilities revealed that viruses could be detected in water 1–3 months prior to mortality, enabling early identification of infections through water testing alone. Moreover, the method reliably detected low viral loads (<1 copy) in both water and tissue samples, facilitating preclinical detection and proactive disease management. This approach reduces the risk of mass mortality and economic losses in eel farming. These findings underscore the critical role of advanced molecular diagnostic technologies in enhancing health management in aquaculture.